The Influence of Particle Charge on Heterogeneous Reaction Rate Coefficients

Science.gov (United States)

Aikin, A. C.; Pesnell, W. D.

2000-01-01

The effects of particle charge on heterogeneous reaction rates are presented. Many atmospheric particles, whether liquid or solid are charged. This surface charge causes a redistribution of charge within a liquid particle and as a consequence a perturbation in the gaseous uptake coefficient. The amount of perturbation is proportional to the external potential and the square of the ratio of debye length in the liquid to the particle radius. Previous modeling has shown how surface charge affects the uptake coefficient of charged aerosols. This effect is now included in the heterogeneous reaction rate of an aerosol ensemble. Extension of this analysis to ice particles will be discussed and examples presented.

Zymography methods for visualizing hydrolytic enzymes

OpenAIRE

Vandooren, Jennifer; Geurts, Nathalie; Martens, Erik; Van den Steen, Philippe E.; Opdenakker, Ghislain

2013-01-01

Zymography is a technique for studying hydrolytic enzymes on the basis of substrate degradation. It is a powerful., but often misinterpreted, tool. yielding information on potential. hydrolytic activities, enzyme forms and the locations of active enzymes. In this Review, zymography techniques are compared in terms of advantages, limitations and interpretations. With in gel zymography, enzyme forms are visualized according to their molecular weights. Proteolytic activities are localized in tis...

Stability and dynamics of reactors with heterogeneously catalyzed reactions

Energy Technology Data Exchange (ETDEWEB)

Eigenberger, G [BASF A.G., Ludwigshafen am Rhein (Germany, F.R.)

1978-12-01

Our knowledge of causes and consequences of problems arising from instability and dynamic effects in reactors with heterogeneously catalyzed reactions has increased remarkably in recent years. Especially thermal effects, caused by the self-acceleration of an exothermic reaction in combination with heat and mass transport, are now well understood. In addition, kinetic effects, i.e. phenomena which have to be explained by the kinetic peculiarities of surface reactions, have attracted increasing interest. For both cases the state of the art will be reviewed, highlighting the physical and chemical causes of the observed phenomena.

Relative mobility of 1-H atoms of carbohydrates in heterogeneous isotope exchange reactions

International Nuclear Information System (INIS)

Akulov, G.P.; Snetkova, E.V.; Kayumov, V.G.; Kaminskii, Yu.L.

1988-01-01

The method of competitive reactions was used to determine the relative mobilities of the 1-H atoms of carbohydrates in reactions of heterogeneous isotope exchange, using various reference standards, catalysts, and buffer systems. On the basis of the results obtained, the investigated carbohydrates are ranged in a series of decreasing mobility of the hydrogen atoms exchanged in heterogeneous isotope exchange reactions. It was demonstrated that the mobility of the 1-H atoms is related to the concentration of the acyclic forms of the carbohydrates

Numerical study of homogeneous–heterogeneous reactions in Sisko fluid flow past a stretching cylinder

Directory of Open Access Journals (Sweden)

Rabia Malik

2018-03-01

Full Text Available The motivation behind the present study is to focus on the effects of stagnation-point flow and heat transfer to the Sisko fluid past an impermeable stretching cylinder involving convective boundary conditions with homogeneous–heterogeneous reactions. Diffusion coefficients of species A and B are assumed to be of the same size. Also, it is assumed that heat released during chemical reaction is negligible. A system of governing ordinary differential equations is obtained by using suitable transformations which are then solved numerically by means of the shooting method combined with Runge-Kutta method. The obtained numerical results are then presented in graphical and tabular form and are discussed at length. The results obtained reveal that the concentration profile decreases with increasing homogeneous and heterogeneous reactions parameters. Keywords: Homogeneous–heterogeneous reactions, Non-linearly stretching cylinder, Stagnation-point flow, Convective boundary conditions, Sisko fluid

Non-hydrolytic metal oxide films for perovskite halide overcoating and stabilization

Science.gov (United States)

Martinson, Alex B.; Kim, In Soo

2017-09-26

A method of protecting a perovskite halide film from moisture and temperature includes positioning the perovskite halide film in a chamber. The chamber is maintained at a temperature of less than 200 degrees Celsius. An organo-metal compound is inserted into the chamber. A non-hydrolytic oxygen source is subsequently inserted into the chamber. The inserting of the organo-metal compound and subsequent inserting of the non-hydrolytic oxygen source into the chamber is repeated for a predetermined number of cycles. The non-hydrolytic oxygen source and the organo-metal compound interact in the chamber to deposit a non-hydrolytic metal oxide film on perovskite halide film. The non-hydrolytic metal oxide film protects the perovskite halide film from relative humidity of greater than 35% and a temperature of greater than 150 degrees Celsius, respectively.

Tribological study of a highly hydrolytically stable phenylboronic acid ester containing benzothiazolyl in mineral oil

International Nuclear Information System (INIS)

Li, Zhipeng; Li, Xiufeng; Zhang, Yawen; Ren, Tianhui; Zhao, Yidong; Zeng, Xiangqiong; Heide, E. van der

2014-01-01

A novel long chain alkyl phenylboronic acid ester containing heterocyclic compound, bis (1-(benzothiazol-2-ylthio) propan-2-yl)-4-dodecylphenylboronic acid ester (DBBMT), was synthesized and characterized. The hydrolytic stability of the DBBMT was evaluated and the results show that DBBMT is of outstanding hydrolytic stability compared with normal borate esters, which indicates that the designed molecular structure, by introducing benzene ring to conjugate with the electron-deficient boron and the benzothiazole as a hinder group, is effective on obtaining a hydrolytically stable long chain alkyl phenylboronic acid ester. The tribological properties of DBBMT and ZDDP in mineral base oil were evaluated using a four-ball tribometer, which suggests that the DBBMT possesses comprehensive tribological properties and could be a potential candidate for the replacement of ZDDP. Furthermore, in order to understand the tribological behaviors, the worn surface was analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) spectroscopy. The results indicate that the elements S, B, O and Fe perform complicated tribochemical reactions to form the compact tribological film composed of B 2 O 3 , FeS, Fe 3 O 4 and FeSO 4 .

Heterogeneity across emerging market central bank reaction functions

Directory of Open Access Journals (Sweden)

Mesut Turkay

2017-09-01

Full Text Available The purpose of this study is to analyze monetary policy reaction functions of inflation targeting emerging market economies. Heterogeneity across central bank behavior is modelled using dynamic common correlated effects estimator in a panel data framework of 15 countries. The empirical method allows us to obtain country specific coefficients and shows differences across central bank reaction functions. Model results imply that central banks behave according to an extended Taylor rule and respond to deviation of inflation from the target, output gap, real exchange rate and external financial conditions. The study finds that emerging market central banks consider not only price stability, but also financial stability in setting of interest rates.

Zymography methods for visualizing hydrolytic enzymes.

Science.gov (United States)

Vandooren, Jennifer; Geurts, Nathalie; Martens, Erik; Van den Steen, Philippe E; Opdenakker, Ghislain

2013-03-01

Zymography is a technique for studying hydrolytic enzymes on the basis of substrate degradation. It is a powerful, but often misinterpreted, tool yielding information on potential hydrolytic activities, enzyme forms and the locations of active enzymes. In this Review, zymography techniques are compared in terms of advantages, limitations and interpretations. With in gel zymography, enzyme forms are visualized according to their molecular weights. Proteolytic activities are localized in tissue sections with in situ zymography. In vivo zymography can pinpoint proteolytic activity to sites in an intact organism. Future development of novel substrate probes and improvement in detection and imaging methods will increase the applicability of zymography for (reverse) degradomics studies.

Physico-chemical and thermochemical studies of the hydrolytic conversion of amorphous tricalcium phosphate into apatite

International Nuclear Information System (INIS)

Somrani, Saida; Banu, Mihai; Jemal, Mohamed; Rey, Christian

2005-01-01

The conversion of amorphous tricalcium phosphate with different hydration ratio into apatite in water at 25 deg. C has been studied by microcalorimetry and several physical-chemical methods. The hydrolytic transformation was dominated by two strong exothermic events. A fast, relatively weak, wetting process and a very slow but strong heat release assigned to a slow internal rehydration and the crystallization of the amorphous phase into an apatite. The exothermic phenomenon related to the rehydration exceeded the crystalline transformation enthalpy. Rehydration occurred before the conversion of the amorphous phase into apatite and determined the advancement of the hydrolytic reaction. The apatitic phases formed evolved slightly with time after their formation. The crystallinity increased whereas the amount of HPO 4 2- ion decreased. These data allow a better understanding of the behavior of biomaterials involving amorphous phases such as hydroxyapatite plasma-sprayed coatings

Exchange reaction between hydrogen and deuterium. II - Proposal for an heterogeneous initiation mechanism of gaseous phase reactions

Energy Technology Data Exchange (ETDEWEB)

Marteau, Chantal; Gaillard-Cusin, Francoise; James, Henri [Centre National de la Recherche Scientifique, 45 - Orleans-la-Source (France). Centre de Recherches sur la Chimie de Combustion et des Hautes Temperatures

1978-05-01

Investigation of experimental data related to evolution period exhibited by H/sub 2/-D/sub 2/ exchange process requires to take into account the variation against time of every atomic species -adsorbed or not- implied in the reaction mechanism. The formation of first chain carriers involves: - chemisorption of either gaseous reactant on the surface active centres (..sigma..), e.g.: ..sigma.. + 1/2 H/sub 2/ reversible ..sigma..H; - consecutive generation of atomic species through hetero-homogeneous transfer between chemisorbed species (..sigma..H) and gaseous molecules: ..sigma..H+H/sub 2/..--> sigma..+H/sub 2/+H/sup 0/, ..sigma..H+D/sub 2/..--> sigma..+HD+D/sup 0/. Therefore, it can be shown that the heterogeneous initiation process of a gas phase reaction identifies to a chain linear mechanism. Such an heterogeneous sequence conditions the further proceeding of the homogeneous chain reaction; both evolutions being kinematically connected. Rate constant of hydrogen adsorption on silica glass: ksub(a1) approximately 10/sup 14/ exp(-47/RT)Isup(0,5).molesup(-0,5).S/sup -1/ has been evaluated.

Impact of Cattaneo-Christov Heat Flux in Jeffrey Fluid Flow with Homogeneous-Heterogeneous Reactions.

Directory of Open Access Journals (Sweden)

Tasawar Hayat

Full Text Available Two-dimensional stretched flow of Jeffrey fluid in view of Cattaneo-Christov heat flux is addressed. Effects of homogeneous-heterogeneous reactions are also considered. Suitable transformations are used to form ordinary differential equations. Convergent series solutions are computed. Impact of significant parameters on the velocity, temperature, concentration and skin friction coefficient is addressed. Analysis of thermal relaxation is made. The obtained results show that ratio of relaxation to retardation times and Deborah number have inverse relation for velocity profile. Temperature distribution has decreasing behavior for Prandtl number and thermal relaxation time. Also concentration decreases for larger values of strength of homogeneous reaction parameter while it increases for strength of heterogeneous reaction parameter.

Impact of Cattaneo-Christov Heat Flux in Jeffrey Fluid Flow with Homogeneous-Heterogeneous Reactions.

Science.gov (United States)

Hayat, Tasawar; Qayyum, Sumaira; Imtiaz, Maria; Alsaedi, Ahmed

2016-01-01

Two-dimensional stretched flow of Jeffrey fluid in view of Cattaneo-Christov heat flux is addressed. Effects of homogeneous-heterogeneous reactions are also considered. Suitable transformations are used to form ordinary differential equations. Convergent series solutions are computed. Impact of significant parameters on the velocity, temperature, concentration and skin friction coefficient is addressed. Analysis of thermal relaxation is made. The obtained results show that ratio of relaxation to retardation times and Deborah number have inverse relation for velocity profile. Temperature distribution has decreasing behavior for Prandtl number and thermal relaxation time. Also concentration decreases for larger values of strength of homogeneous reaction parameter while it increases for strength of heterogeneous reaction parameter.

Impact of supersonic and subsonic aircraft on ozone: Including heterogeneous chemical reaction mechanisms

International Nuclear Information System (INIS)

Kinnison, D.E.; Wuebbles, D.J.

1992-01-01

Preliminary calculations suggest that heterogeneous reactions are important in calculating the impact on ozone from emissions of trace gases from aircraft fleets. In this study, three heterogeneous chemical processes that occur on background sulfuric acid aerosols are included and their effects on O 3 , NO x , Cl x , HCl, N 2 O 5 , ClONO 2 are calculated

Molecular Imaging of Hydrolytic Enzymes Using PET and SPECT.

Science.gov (United States)

Rempel, Brian P; Price, Eric W; Phenix, Christopher P

2017-01-01

Hydrolytic enzymes are a large class of biological catalysts that play a vital role in a plethora of critical biochemical processes required to maintain human health. However, the expression and/or activity of these important enzymes can change in many different diseases and therefore represent exciting targets for the development of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) radiotracers. This review focuses on recently reported radiolabeled substrates, reversible inhibitors, and irreversible inhibitors investigated as PET and SPECT tracers for imaging hydrolytic enzymes. By learning from the most successful examples of tracer development for hydrolytic enzymes, it appears that an early focus on careful enzyme kinetics and cell-based studies are key factors for identifying potentially useful new molecular imaging agents.

Heterogeneous-catalytic redox reactions in nitrate - formate systems

International Nuclear Information System (INIS)

Ananiev, A.V.; Shilov, V.P.; Tananaev, I.G.; Brossard, Ph.; Broudic, J.Ch.

2000-01-01

It was found that an intensive destruction of various organic and mineral substances - usual components of aqueous waste solutions (oxalic acid, complexones, urea, hydrazine, ammonium nitrate, etc.) takes place under the conditions of catalytic denitration. Kinetics and mechanisms of urea and ammonium nitrate decomposition in the system HNO 3 - HCOOH - Pt/SiO 2 are comprehensively investigated. The behaviour of uranium, neptunium and plutonium under the conditions of catalytic denitration is studied. It is shown, that under the certain conditions the formic acid is an effective reducer of the uranium (VI), neptunium (VI, V) and plutonium (VI, IV) ions. Kinetics of heterogeneous-catalytic red-ox reactions of uranium (VI), neptunium (VI, V) and plutonium (VI, IV) with formic acid are investigated. The mechanisms of the appropriate reactions are evaluated. (authors)

Technological advances and applications of hydrolytic enzymes for valorization of lignocellulosic biomass.

Science.gov (United States)

Manisha; Yadav, Sudesh Kumar

2017-12-01

Hydrolytic enzymes are indispensable tools in the production of various foodstuffs, drugs, and consumables owing to their applications in almost every industrial process nowadays. One of the foremost areas of interest involving the use of hydrolytic enzymes is in the transformation of lignocellulosic biomass into value added products. However, limitations of the processes due to inadequate enzyme activity and stability with a narrow range of pH and temperature optima often limit their effective usage. The innovative technologies, involving manipulation of enzyme activity and stability through mutagenesis, genetic engineering and metagenomics lead to a major leap in all the fields using hydrolytic enzymes. This article provides recent advancement towards the isolation and use of microbes for lignocellulosic biomass utilisation, microbes producing the hydrolytic enzymes, the modern age technologies used to manipulate and enhance the hydrolytic enzyme activity and the applications of such enzymes in value added products development from lignocellulosic biomass. Copyright © 2017 Elsevier Ltd. All rights reserved.

Outcome of homogeneous and heterogeneous reactions in Darcy-Forchheimer flow with nonlinear thermal radiation and convective condition

Directory of Open Access Journals (Sweden)

T. Hayat

Full Text Available The present analysis aims to report the consequences of nonlinear radiation, convective condition and heterogeneous-homogeneous reactions in Darcy-Forchheimer flow over a non-linear stretching sheet with variable thickness. Non-uniform magnetic field and nonuniform heat generation/absorption are accounted. The governing boundary layer partial differential equations are converted into a system of nonlinear ordinary differential equations. The computations are organized and the effects of physical variables such as thickness parameter, power index, Hartman number, inertia and porous parameters, radiation parameter, Biot number, Prandtl number, ratio parameter, heat generation parameter and homogeneous-heterogeneous reaction parameter are investigated. The variations of skin friction coefficient and Nusselt number for different interesting variables are plotted and discussed. It is noticed that Biot number and heat generation variable lead to enhance the temperature distribution. The solutal boundary layer thickness decreases for larger homogeneous variable while reverse trend is seen for heterogeneous reaction. Keywords: Variable sheet thickness, Darcy-Forchheimer flow, Homogeneous-heterogeneous reactions, Power-law surface velocity, Convective condition, Heat generation/absorption, Nonlinear radiation

Investigation of heterogeneous reactions of NO2 on aqueous surfaces

International Nuclear Information System (INIS)

Mertes, S.

1992-01-01

A microjet apparatus was developed for the purpose of measuring the loss in the gaseous phase and the uptake in the liquid phase of nitrogen on the basis of heterogeneous processes on a liquid surface. The measurements were to provide information on the mass accomodation coefficient α and on assumed surface reactions of NO 2 . (orig./BBR) [de

Heterogeneous Reactions between Toluene and NO2 on Mineral Particles under Simulated Atmospheric Conditions.

Science.gov (United States)

Niu, Hejingying; Li, Kezhi; Chu, Biwu; Su, Wenkang; Li, Junhua

2017-09-05

Heterogeneous reactions between organic and inorganic gases with aerosols are important for the study of smog occurrence and development. In this study, heterogeneous reactions between toluene and NO 2 with three atmospheric mineral particles in the presence or absence of UV light were investigated. The three mineral particles were SiO 2 , α-Fe 2 O 3 , and BS (butlerite and szmolnokite). In a dark environment, benzaldehyde was produced on α-Fe 2 O 3 . For BS, nitrotoluene and benzaldehyde were obtained. No aromatic products were produced in the absence of NO 2 in the system. In the presence of UV irradiation, benzaldehyde was detected on the SiO 2 surface. Identical products were produced in the presence and absence of UV light over α-Fe 2 O 3 and BS. UV light promoted nitrite to nitrate on mineral particles surface. On the basisi of the X-ray photoelectron spectroscopy (XPS) results, a portion of BS was reduced from Fe 3+ to Fe 2+ with the adsorption of toluene or the reaction with toluene and NO 2 . Sulfate may play a key role in the generation of nitrotoluene on BS particles. From this research, the heterogeneous reactions between organic and inorganic gases with aerosols that occur during smog events will be better understood.

A model for hydrolytic degradation and erosion of biodegradable polymers.

Science.gov (United States)

Sevim, Kevser; Pan, Jingzhe

2018-01-15

For aliphatic polyesters such as PLAs and PGAs, there is a strong interplay between the hydrolytic degradation and erosion - degradation leads to a critically low molecular weight at which erosion starts. This paper considers the underlying physical and chemical processes of hydrolytic degradation and erosion. Several kinetic mechanisms are incorporated into a mathematical model in an attempt to explain different behaviours of mass loss observed in experiments. In the combined model, autocatalytic hydrolysis, oligomer production and their diffusion are considered together with surface and interior erosion using a set of differential equations and Monte Carlo technique. Oligomer and drug diffusion are modelled using Fick's law with the diffusion coefficients dependent on porosity. The porosity is due to the formation of cavities which are a result of polymer erosion. The model can follow mass loss and drug release up to 100%, which cannot be explained using a simple reaction-diffusion. The model is applied to two case studies from the literature to demonstrate its validity. The case studies show that a critical molecular weight for the onset of polymer erosion and an incubation period for the polymer dissolution are two critical factors that need to be considered when predicting mass loss and drug release. In order to design bioresorbable implants, it is important to have a mathematical model to predict polymer degradation and corresponding drug release. However, very different behaviours of polymer degradation have been observed and there is no single model that can capture all these behaviours. For the first time, the model presented in this paper is capable of capture all these observed behaviours by switching on and off different underlying mechanisms. Unlike the existing reaction-diffusion models, the model presented here can follow the degradation and drug release all the way to the full disappearance of an implant. Crown Copyright © 2017. Published by

Determination of kinetic parameters of heterogeneous isotopic exchange reaction

International Nuclear Information System (INIS)

Huang, Ting-Chia; Tsai, Fuan-Nan

1977-01-01

A mathematical model has been proposed for a heterogeneous isotopic exchange reaction which involves film diffusion, surface chemical reaction and intraparticle diffusion. The exchange equation to predict the exchange fraction as a function of time for the spherical particles immersed in a solution of finite volume has been derived. The relations between the exchange fraction and dimensionless time are plotted with xi(=ak sub(f)/KD sub(e)), xi 1 (=K 1 a 2 /D sub(e)) and final fractional uptake as parameters. From the values of the kinetic parameters xi and xi 1 , the relative importance of each limiting step is discussed. Experimental results of the isotopic exchange reaction of calcium ion in both system CaCO 3 (s)/Ca 2+ (aq) and system calcium type resin Dowex 50W-X8/Ca 2+ (aq) are coincident with the theoretical equation proposed in this study. (auth.)

Kinetic investigation of heterogeneous catalytic reactions by means of the kinetic isotope method

Energy Technology Data Exchange (ETDEWEB)

Bauer, F; Dermietzel, J [Akademie der Wissenschaften der DDR, Leipzig. Zentralinstitut fuer Isotopen- und Strahlenforschung

1978-09-01

The application of the kinetic isotope method to heterogeneous catalytic processes is possible for surface compounds by using the steady-state relation. However, the characterization of intermediate products becomes ambiguous if sorption rates are of the same order of magnitude as surface reactions rates. The isotopic exchange reaction renders possible the estimation of sorption rates.

Heterogeneous reaction of particulate chlorpyrifos with NO3 radicals: Products, pathways, and kinetics

Science.gov (United States)

Li, Nana; Zhang, Peng; Yang, Bo; Shu, Jinian; Wang, Youfeng; Sun, Wanqi

2014-08-01

Chlorpyrifos is a typical chlorinated organophosphorus pesticide. The heterogeneous reaction of chlorpyrifos particles with NO3 radicals was investigated using a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) and a real-time atmospheric gas analysis mass spectrometer. Chlorpyrifos oxon, 3,5,6-trichloro-2-pyridinol, O,O-diethyl O-hydrogen phosphorothioate, O,O-diethyl ester thiophosphoric acid, diethyl hydrogen phosphate and a phosphinyl disulfide compound were identified as the main degradation products. The heterogeneous reaction pathways were proposed and their kinetic processes were investigated via a mixed-phase relative rate method. The observed effective rate constant is 3.4 ± 0.2 × 10-12 cm3 molecule-1 s-1.

Non-Enzymatic biopolymerization reactions supported by heterogeneous media

DEFF Research Database (Denmark)

Monnard, Pierre-Alain

2011-01-01

Heterogeneous media, such as micro-structured aqueous environments, could offer an alternative approach to the synthesis of biopolymers with novel functions. Structured media are here defined as specialized, self-assembled structures that are formed, e.g, by amphiphiles, such as liposomes, emulsion...... compartments and lipid-bilayer lattices. Another kind of media is represented by co-existing, self-assembled phases in the reaction medium, e.g., in water-ice matrices. These media have the capacity to assemble chemical molecules or complex catalytic assemblies into unique configurations that are unstable...

Endoscopy and homogeneous-heterogeneous reactions in MHD radiative peristaltic activity of Ree-Eyring fluid

Science.gov (United States)

Hayat, Tasawar; Akram, Javaria; Alsaedi, Ahmed; Zahir, Hina

2018-03-01

Endoscopic and homogeneous-heterogeneous reactions in MHD peristalsis of Ree-Eyring fluid are addressed. Mathematical modeling and analysis have been performed by utilizing cylindrical coordinates. Nonlinear thermal radiation is present. Impact of slip boundary conditions on temperature and velocity on outer tube are taken into consideration. Lubrication approach is employed. The nonlinear system is executed numerically for solutions of velocity, temperature and concentration. Graphical results are obtained to predict physical interpretation of various embedded parameters. It is noted that homogeneous and heterogeneous reactions affect the concentration alternatively. Moreover Brinkman number rises the temperature and heat transfer coefficient whereas thermal slip drops temperature and heat transfer rate.

Chemical kinetics: on the heterogeneous catalysis processes leading to an exchange between two phases. Example: isotopic exchange reactions; Cinetique chimique: sur les processus de catalyse 'heterogene' conduisant a un echange entre deux phases. Exemple: reactions d'echange isotopique

Energy Technology Data Exchange (ETDEWEB)

Dirian, G; Grandcollot, P [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1961-07-01

For an exchange reaction between a gaseous and a liquid phase proceeding by 'heterogeneous' catalysis in the liquid phase, diffusion in the liquid and the chemical reaction are two simultaneous and indivisible processes. We have nevertheless been able to establish criteria making it possible to distinguish between a really homogeneous kinetic process and a pseudo-homogeneous one. (author) [French] Pour une reaction d'echange entre une phase gazeuse et une phase liquide procedant par catalyse 'heterogene' en phase liquide, la diffusion dans le liquide et la reaction chimique sont deux etapes simultanees et indissociables. Nous avons pu neanmoins etablir des criteres permettant de distinguer entre une cinetique homogene vraie et une cinetique pseudo-homogene. (auteur)

Darcy-Forchheimer flow with Cattaneo-Christov heat flux and homogeneous-heterogeneous reactions.

Science.gov (United States)

Hayat, Tasawar; Haider, Farwa; Muhammad, Taseer; Alsaedi, Ahmed

2017-01-01

Here Darcy-Forchheimer flow of viscoelastic fluids has been analyzed in the presence of Cattaneo-Christov heat flux and homogeneous-heterogeneous reactions. Results for two viscoelastic fluids are obtained and compared. A linear stretching surface has been used to generate the flow. Flow in porous media is characterized by considering the Darcy-Forchheimer model. Modified version of Fourier's law through Cattaneo-Christov heat flux is employed. Equal diffusion coefficients are employed for both reactants and auto catalyst. Optimal homotopy scheme is employed for solutions development of nonlinear problems. Solutions expressions of velocity, temperature and concentration fields are provided. Skin friction coefficient and heat transfer rate are computed and analyzed. Here the temperature and thermal boundary layer thickness are lower for Cattaneo-Christov heat flux model in comparison to classical Fourier's law of heat conduction. Moreover, the homogeneous and heterogeneous reactions parameters have opposite behaviors for concentration field.

Coupled enzyme reactions performed in heterogeneous reaction media: experiments and modeling for glucose oxidase and horseradish peroxidase in a PEG/citrate aqueous two-phase system.

Science.gov (United States)

Aumiller, William M; Davis, Bradley W; Hashemian, Negar; Maranas, Costas; Armaou, Antonios; Keating, Christine D

2014-03-06

The intracellular environment in which biological reactions occur is crowded with macromolecules and subdivided into microenvironments that differ in both physical properties and chemical composition. The work described here combines experimental and computational model systems to help understand the consequences of this heterogeneous reaction media on the outcome of coupled enzyme reactions. Our experimental model system for solution heterogeneity is a biphasic polyethylene glycol (PEG)/sodium citrate aqueous mixture that provides coexisting PEG-rich and citrate-rich phases. Reaction kinetics for the coupled enzyme reaction between glucose oxidase (GOX) and horseradish peroxidase (HRP) were measured in the PEG/citrate aqueous two-phase system (ATPS). Enzyme kinetics differed between the two phases, particularly for the HRP. Both enzymes, as well as the substrates glucose and H2O2, partitioned to the citrate-rich phase; however, the Amplex Red substrate necessary to complete the sequential reaction partitioned strongly to the PEG-rich phase. Reactions in ATPS were quantitatively described by a mathematical model that incorporated measured partitioning and kinetic parameters. The model was then extended to new reaction conditions, i.e., higher enzyme concentration. Both experimental and computational results suggest mass transfer across the interface is vital to maintain the observed rate of product formation, which may be a means of metabolic regulation in vivo. Although outcomes for a specific system will depend on the particulars of the enzyme reactions and the microenvironments, this work demonstrates how coupled enzymatic reactions in complex, heterogeneous media can be understood in terms of a mathematical model.

Heterogeneity induces spatiotemporal oscillations in reaction-diffusion systems

Science.gov (United States)

Krause, Andrew L.; Klika, Václav; Woolley, Thomas E.; Gaffney, Eamonn A.

2018-05-01

We report on an instability arising in activator-inhibitor reaction-diffusion (RD) systems with a simple spatial heterogeneity. This instability gives rise to periodic creation, translation, and destruction of spike solutions that are commonly formed due to Turing instabilities. While this behavior is oscillatory in nature, it occurs purely within the Turing space such that no region of the domain would give rise to a Hopf bifurcation for the homogeneous equilibrium. We use the shadow limit of the Gierer-Meinhardt system to show that the speed of spike movement can be predicted from well-known asymptotic theory, but that this theory is unable to explain the emergence of these spatiotemporal oscillations. Instead, we numerically explore this system and show that the oscillatory behavior is caused by the destabilization of a steady spike pattern due to the creation of a new spike arising from endogeneous activator production. We demonstrate that on the edge of this instability, the period of the oscillations goes to infinity, although it does not fit the profile of any well-known bifurcation of a limit cycle. We show that nearby stationary states are either Turing unstable or undergo saddle-node bifurcations near the onset of the oscillatory instability, suggesting that the periodic motion does not emerge from a local equilibrium. We demonstrate the robustness of this spatiotemporal oscillation by exploring small localized heterogeneity and showing that this behavior also occurs in the Schnakenberg RD model. Our results suggest that this phenomenon is ubiquitous in spatially heterogeneous RD systems, but that current tools, such as stability of spike solutions and shadow-limit asymptotics, do not elucidate understanding. This opens several avenues for further mathematical analysis and highlights difficulties in explaining how robust patterning emerges from Turing's mechanism in the presence of even small spatial heterogeneity.

Drift mechanism of mass transfer on heterogeneous reaction in crystalline silicon substrate

Energy Technology Data Exchange (ETDEWEB)

Kukushkin, S.A. [Institute of Problems of Mechanical Engineering, Russian Academy of Science, St Petersburg, 199178 (Russian Federation); St. Petersburg National Research University of Information Technologies, Mechanics and Optics, 197101 (Russian Federation); Osipov, A.V., E-mail: Andrey.V.Osipov@gmail.com [Institute of Problems of Mechanical Engineering, Russian Academy of Science, St Petersburg, 199178 (Russian Federation); St. Petersburg National Research University of Information Technologies, Mechanics and Optics, 197101 (Russian Federation)

2017-05-01

This work aims to study the pressure dependence of the thickness of the epitaxial silicon carbide film growing from crystalline silicon due to the heterogeneous reaction with gaseous carbon monoxide. It turned out that this dependence exhibits the clear maximum. On further pressure increasing the film thickness decreases. The theoretical model has been developed which explains such a character of the dependence by the fact that the gaseous silicon monoxide reaction product inhibits the drift of the gaseous reagent through the channels of a crystal lattice, thus decreasing their hydraulic diameter. In the proposed hydraulic model, the dependences of the film thickness both on the gas pressure and time have been calculated. It was shown that not only the qualitative but also quantitative correspondence between theoretical and experimental results takes place. As one would expect, due to the Einstein relation, at short growth times the drift model coincides with the diffusion one. Consequences of this drift mechanism of epitaxial film growing are discussed. - Graphical abstract: This work aims to study the pressure dependence of the thickness of the epitaxial silicon carbide film growing from crystalline silicon due to the heterogeneous reaction with gaseous carbon monoxide. It turned out that this dependence exhibits the clear maximum. On further pressure increasing the film thickness decreases. The theoretical model has been developed which explains such a character of the dependence by the fact that the gaseous silicon monoxide reaction product inhibits the drift of the gaseous reagent through the channels of a crystal lattice, thus decreasing their hydraulic diameter. - Highlights: • It is established that the greater pressure, the smaller is the reaction rate. • The reaction product prevents penetration of the reagent into a reaction zone. • For description the hydraulic model of crystal lattice channels is developed. • Theoretical results for polytropic

Kinetic investigation on enantioselective hydrolytic resolution of ...

African Journals Online (AJOL)

Kinetic investigation on enantioselective hydrolytic resolution of epichlorohydrin by crude epoxide hydrolase from domestic duck liver. X Ling, D Lu, J Wang, J Chen, L Ding, J Chen, H Chai, P Ouyang ...

Heterogeneous reactions of ozone with methoxyphenols, in presence and absence of light

Science.gov (United States)

Net, Sopheak; Alvarez, Elena Gómez; Gligorovski, Sasho; Wortham, Henri

2011-06-01

In this work, we investigated the heterogeneous reactions between gaseous ozone and seven particulate methoxyphenols, biomass tracers. The ozonolysis of silica particles coated with vanillin, vanillic acid, syringaldehyde, syringic acid, acetovanillone, acetonsyringone and coniferyl alcohol was studied successively and was carried out both in total darkness and under illumination with simulated solar light at 297 K. The condensed-phase products which emerged in such heterogeneous reactions were analyzed by gas chromatography-mass spectrometry (GC/MS). No reaction product was detected during the ozonolysis of vanillic acid, syringic acid, acetovanillone and acetosyringone under our experimental conditions. The main tranformation of pathway vanillin and syringaldehyde was the conversion of an aldehyde group to a carboxylic fonction. Thus, syringic acid and vanillic acid were respectively the main oxidation products of syringaldehyde and vanillin. The oxidation of coniferyl alcohol was relatively fast and the total degradation was observed after 16 h of ozone exposure. Five oxidation products: glycolic acid, oxalic acid, vanillin, vanillic acid and 3,4-dihydroxybenzoic acid, were identified and confirmed by their corresponding standards. It is interesting to note that 3,4-dihydroxybenzoic acid was detected only in the experiment performed under combined ozone and light exposure of the particles coated with coniferyl alcohol. Vanillin and vanillic acid also absorb light in the tropospheric actinic window and therefore they can be photochemically active which in turn can induce further modifications of the aerosol particles. A mechanistic pathway was proposed in order to elucidate the ozonolysis reaction of coniferyl alcohol and to explain the identified reaction products.

Outcome of homogeneous and heterogeneous reactions in Darcy-Forchheimer flow with nonlinear thermal radiation and convective condition

Science.gov (United States)

Hayat, T.; Shah, Faisal; Alsaedi, A.; Hussain, Zakir

The present analysis aims to report the consequences of nonlinear radiation, convective condition and heterogeneous-homogeneous reactions in Darcy-Forchheimer flow over a non-linear stretching sheet with variable thickness. Non-uniform magnetic field and nonuniform heat generation/absorption are accounted. The governing boundary layer partial differential equations are converted into a system of nonlinear ordinary differential equations. The computations are organized and the effects of physical variables such as thickness parameter, power index, Hartman number, inertia and porous parameters, radiation parameter, Biot number, Prandtl number, ratio parameter, heat generation parameter and homogeneous-heterogeneous reaction parameter are investigated. The variations of skin friction coefficient and Nusselt number for different interesting variables are plotted and discussed. It is noticed that Biot number and heat generation variable lead to enhance the temperature distribution. The solutal boundary layer thickness decreases for larger homogeneous variable while reverse trend is seen for heterogeneous reaction.

Heterogeneous reactions of carbonyl sulfide on mineral oxides: mechanism and kinetics study

Directory of Open Access Journals (Sweden)

Y. Liu

2010-11-01

Full Text Available The heterogeneous reactions of carbonyl sulfide (OCS on the typical mineral oxides in the mineral dust particles were investigated using a Knudsen cell flow reactor and a diffuse reflectance UV-vis spectroscopy. The reaction pathway for OCS on mineral dust was identified based on the gaseous products and surface species. The hydrolysis of OCS and succeeding oxidation of intermediate products readily took place on α-Al₂O₃, MgO, and CaO. Reversible and irreversible adsorption of OCS were observed on α-Fe₂O₃ and ZnO, respectively, whereas no apparent uptake of OCS by SiO₂ and TiO₂ was observed. The reactivity of OCS on these oxides depends on both the basicity of oxides and the decomposition reactivity of oxides for H₂S. Based on the individual uptake coefficients and chemical composition of authentic mineral dust, the uptake coefficient (γ_BET of mineral dust was estimated to be in the range of 3.84×10⁻⁷–2.86×10⁻⁸. The global flux of OCS due to heterogeneous reactions and adsorption on mineral dust was estimated at 0.13–0.29 Tg yr⁻¹, which is comparable to the annual flux of OCS for its reaction with ·OH.

Kinetics study of heterogeneous reactions of ozone with erucic acid using an ATR-IR flow reactor.

Science.gov (United States)

Leng, Chunbo; Hiltner, Joseph; Pham, Hai; Kelley, Judas; Mach, Mindy; Zhang, Yunhong; Liu, Yong

2014-03-07

The ozone initiated heterogeneous oxidation of erucic acid (EA) thin film was investigated using a flow system combined with attenuated total reflection infrared spectroscopy (ATR-IR) over wide ranges of ozone concentrations (0.25-60 ppm), thin film thickness (0.1-1.0 μm), temperatures (263-298 K), and relative humidities (0-80% RH) for the first time. Pseudo-first-order rate constants, kapp, and overall reactive uptake coefficients, γ, were obtained through changes in the absorbance of C[double bond, length as m-dash]O stretching bands at 1695 cm(-1), which is assigned to the carbonyl group in carboxylic acid. Results showed that the reaction followed the Langmuir-Hinshelwood mechanism and kapp was largely dominated by surface reaction over bulk phase reaction. In addition, both the kapp and the γ values showed very strong temperature dependences (∼two orders of magnitude) over the temperature range; in contrast, they only slightly increased with increasing RH values from 0-80%. According to the kapp values as a function of temperature, the activation energy for the heterogeneous reaction was estimated to be 80.6 kJ mol(-1). Our results have suggested that heterogeneous reactions between ozone and unsaturated solid surfaces likely have a substantially greater temperature dependence than liquid ones. Moreover, the hygroscopic properties of EA thin films before and after exposure to ozone were also studied by measurement of water uptake. Based on the hygroscopicity data, the insignificant RH effect on reaction kinetics was probably due to the relatively weak water uptake by the unreacted and reacted EA thin films.

Mitoxantrone removal by electrochemical method: A comparison of homogenous and heterogenous catalytic reactions

Directory of Open Access Journals (Sweden)

Abbas Jafarizad

2017-08-01

Full Text Available Background: Mitoxantrone (MXT is a drug for cancer therapy and a hazardous pharmaceutical to the environment which must be removed from contaminated waste streams. In this work, the removal of MXT by the electro-Fenton process over heterogeneous and homogenous catalysts is reported. Methods: The effects of the operational conditions (reaction medium pH, catalyst concentration and utilized current intensity were studied. The applied electrodes were carbon cloth (CC without any processing (homogenous process, graphene oxide (GO coated carbon cloth (GO/CC (homogenous process and Fe3O4@GO nanocomposite coated carbon cloth (Fe3O4@GO/CC (heterogeneous process. The characteristic properties of the electrodes were determined by atomic force microscopy (AFM, field emission scanning electron microscopy (FE-SEM and cathode polarization. MXT concentrations were determined by using ultraviolet-visible (UV-Vis spectrophotometer. Results: In a homogenous reaction, the high concentration of Fe catalyst (>0.2 mM decreased the MXT degradation rate. The results showed that the Fe3O4@GO/CC electrode included the most contact surface. The optimum operational conditions were pH 3.0 and current intensity of 450 mA which resulted in the highest removal efficiency (96.9% over Fe3O4@GO/CC electrode in the heterogeneous process compared with the other two electrodes in a homogenous process. The kinetics of the MXT degradation was obtained as a pseudo-first order reaction. Conclusion: The results confirmed the high potential of the developed method to purify contaminated wastewaters by MXT.

Hydrolytic And Enzymatic Degradation Characteristics Of Biodegradable Aliphatic Polysters

Institute of Scientific and Technical Information of China (English)

LI Suming

2004-01-01

Aliphatic polyesters, especially those derived from lactide (PLA), glycolide (PGA) and ε-caprolactone (PCL), are being investigated worldwide for applications in the field of surgery (suture material, devices for internal bone fracture fixation), pharmacology (sustained drug delivery systems), and tissue engineering (scaffold for tissue regeneration) [1,2]. This is mainly due to their good biocompatibility and variable degradability. These polymers present also a growing interest for environmental applications in agriculture (mulch films) and in our everyday life (packaging material)as the development of biodegradable materials is now considered as one of the potential solutions to the problem of plastic waste management.For both biomedical and environmental applications, it is of major importance to understand the degradation characteristics of the polymers. The hydrolytic degradation of aliphatic polyesters has been investigated by many research groups. Our group has shown that degradation of PLAGA large size devices is faster inside than at the surface. This heterogeneous degradation is due to the autocatalytic effect of carboxylic endgroups formed by ester bond cleavage. Moreover,degradation-induced morphological and compositional changes were also elucidated. In the case of PCL, the hydrolytic degradation is very slow due to its hydrophobicity and crystallinity.The enzymatic degradation of these polymers has been investigated by a number of authors. A specific enzyme, proteinase K, has been shown to have significant effects on PLA degradation. This enzyme preferentially degrade L-lactate units as opposed to D-lactate ones, amorphous zones as opposed to crystalline ones [3]. The enzymatic degradation of PCL polymers has also been investigated. A number of lipase-type enzymes were found to significantly accelerate the degradation of PCL despite its high crystallinity. In the case of PLA/PCL blends, the two components exhibited well separated crystalline domains

Evaporation rates and surface profiles on heterogeneous surfaces with mass transfer and surface reaction

Energy Technology Data Exchange (ETDEWEB)

Flytzani-Stephanopoulos, M; Schmidt, L D

1979-01-01

Simple models incorporating surface reaction and diffusion of volatile products through a boundary layer are developed to calculate effective rates of evaporation and local surface profiles on surfaces having active and inactive regions. The coupling between surface heterogeneities with respect to a particular reaction and external mass transfer may provide a mechanism for the surface rearrangement and metal loss encountered in several catalytic systems of practical interest. Calculated transport rates for the volatilization of platinum in oxidizing environments and the rearrangement of this metal during the ammonia oxidation reaction agree well with published experimental data.

Reaction-transport simulations of non-oxidative methane conversion with continuous hydrogen removal: Homogeneous-heterogeneous methane reaction pathways

International Nuclear Information System (INIS)

Li, Lin; Borry, Richard W.; Iglesia, Enrique

2000-01-01

Detailed kinetic-transport models were used to explore thermodynamic and kinetic barriers in the non-oxidative conversion of CH4 via homogeneous and homogeneous-heterogeneous pathways and the effects of continuous hydrogen removal and of catalytic sites on attainable yields of useful C2-C10 products. The homogeneous kinetic model combines separately developed models for low-conversion pyrolysis and for chain growth to form large aromatics and carbon. The H2 formed in the reaction decreases CH4 pyrolysis rates and equilibrium conversions and it favors the formation of lighter products. The removal of H2 along tubular reactors with permeable walls increases reaction rates and equilibrium CH4 conversions. C2-C10 yields reach values greater than 90 percent at intermediate values of dimensionless transport rates (delta=1-10), defined as the ratio hydrogen transport and methane conversion rates. Homogeneous reactions require impractical residence times, even with H2 removal, because of slow initiation and chain transfer rates. The introduction of heterogeneous chain initiation pathways using surface sites that form methyl radicals eliminates the induction period without influencing the homogeneous product distribution. Methane conversion, however, occurs predominately in the chain transfer regime, within which individual transfer steps and the formation of C2 intermediates become limited by thermodynamic constraints. Catalytic sites alone cannot overcome these constraints. Catalytic membrane reactors with continuous H2 removal remove these thermodynamic obstacles and decrease the required residence time. Reaction rates become limited by homogeneous reactions of C2 products to form C6+ aromatics. Higher delta values lead to subsequent conversion of the desired C2-C10 products to larger polynuclear aromatics. We conclude that catalytic methane pyrolysis at the low temperatures required for restricted chain growth and the elimination of thermodynamics constraints via

Hydrolytic Activation Kinetics of the Herbicide Benzobicyclon in Simulated Aquatic Systems.

Science.gov (United States)

Williams, Katryn L; Tjeerdema, Ronald S

2016-06-22

Herbicide resistance is a growing concern for weeds in California rice fields. Benzobicyclon (BZB; 3-(2-chloro-4-(methylsulfonyl)benzoyl)-2-phenylthiobicyclo[3.2.1]oct-2-en-4-one) has proven successful against resistant rice field weeds in Asia. A pro-herbicide, BZB forms the active agent, benzobicyclon hydrolysate (BH), in water; however, the transformation kinetics are not understood for aquatic systems, particularly flooded California rice fields. A quantitative experiment was performed to assess the primary mechanism and kinetics of BZB hydrolysis to BH. Complete conversion to BH was observed for all treatments. Basic conditions (pH 9) enhanced the reaction, with half-lives ranging from 5 to 28 h. Dissolved organic carbon (DOC) hindered transformation, which is consistent with other base-catalyzed hydrolysis reactions. BH was relatively hydrolytically stable, with 18% maximum loss after 5 days. Results indicate BZB is an efficient pro-herbicide under aqueous conditions such as those of a California rice field, although application may be best suited for fields with recirculating tailwater systems.

Modeling and simulation of diffusion-convection-reaction in heterogeneous nanochannels using OpenFOAM

NARCIS (Netherlands)

Pimpalgaonkar, H.G.; van Steijn, V.; Kreutzer, M.T.; Kleijn, C.R.; Simos, Theodore; Tsitouras, Charalambos

2016-01-01

We present a finite volume implementation of a phase field method in OpenFOAM as a tool to simulate reactive multiphase flows on heterogeneous surfaces. Using this tool, we simulate the formation and growth of a droplet due to a chemical reaction on a hydrophilic catalytic patch surrounded by a

Nanolithographic Fabrication and Heterogeneous Reaction Studies ofTwo-Dimensional Platinum Model Catalyst Systems

Energy Technology Data Exchange (ETDEWEB)

Contreras, Anthony Marshall [Univ. of California, Berkeley, CA (United States)

2006-05-20

In order to better understand the fundamental components that govern catalytic activity, two-dimensional model platinum nanocatalyst arrays have been designed and fabricated. These catalysts arrays are meant to model the interplay of the metal and support important to industrial heterogeneous catalytic reactions. Photolithography and sub-lithographic techniques such as electron beam lithography, size reduction lithography and nanoimprint lithography have been employed to create these platinum nanoarrays. Both in-situ and ex-situ surface science techniques and catalytic reaction measurements were used to correlate the structural parameters of the system to catalytic activity.

Attainment of chemical equilibrium in effusive beam sources of the heterogeneous reaction type

International Nuclear Information System (INIS)

Hildenbrand, D.L.

1979-01-01

Effusive beam sources derived from gas-solid reactions provide a very important pathway for widening the scope of high temperature thermodynamic studies, but the attainment of chemical equilibrium within these sources is problematical. Some of the underlying kinetic factors associated with the use of these sources are discussed. As one might expect, it is important to maximize the ratio of reactive surface area to exit orifice area. Equilibrium seems to be achieved more readily among the products of gas-solid reactions than among reactant and products, as suggested by the quasi-equilibrium model. Some experiences with the use of heterogeneous reaction sources are described, and two definitive tests for the establishment of equilibrium are outlined

Possibility of increasing the average rate of heterogeneous catalytic reactions by operating in the self-oscillating regime

Energy Technology Data Exchange (ETDEWEB)

Chumakov, G A; Slinko, M G

1979-05-01

The possibility of increasing the average rate of heterogeneous catalytic reactions by operating in the self-oscillating regime was demonstrated by analyzing a kinetic model of hydrogen interaction with oxygen over a metallic catalyst. Within a certain interval of partial pressures of oxygen, the average reaction rate over a period of oscillation may be over five times that of the steady-state reaction.

Kinetics of heterogeneous chemical reactions: a theoretical model for the accumulation of pesticides in soil.

Science.gov (United States)

Lin, S H; Sahai, R; Eyring, H

1971-04-01

A theoretical model for the accumulation of pesticides in soil has been proposed and discussed from the viewpoint of heterogeneous reaction kinetics with a basic aim to understand the complex nature of soil processes relating to the environmental pollution. In the bulk of soil, the pesticide disappears by diffusion and a chemical reaction; the rate processes considered on the surface of soil are diffusion, chemical reaction, vaporization, and regular pesticide application. The differential equations involved have been solved analytically by the Laplace-transform method.

Homogeneous and Heterogeneous Reaction and Transformation of Hg and Trace Metals in Combustion Systems

Energy Technology Data Exchange (ETDEWEB)

J. Helble; Clara Smith; David Miller

2009-08-31

The overall goal of this project was to produce a working dynamic model to predict the transformation and partitioning of trace metals resulting from combustion of a broad range of fuels. The information provided from this model will be instrumental in efforts to identify fuels and conditions that can be varied to reduce metal emissions. Through the course of this project, it was determined that mercury (Hg) and arsenic (As) would be the focus of the experimental investigation. Experiments were therefore conducted to examine homogeneous and heterogeneous mercury oxidation pathways, and to assess potential interactions between arsenic and calcium. As described in this report, results indicated that the role of SO{sub 2} on Hg oxidation was complex and depended upon overall gas phase chemistry, that iron oxide (hematite) particles contributed directly to heterogeneous Hg oxidation, and that As-Ca interactions occurred through both gas-solid and within-char reaction pathways. Modeling based on this study indicated that, depending upon coal type and fly ash particle size, vaporization-condensation, vaporization-surface reaction, and As-CaO in-char reaction all play a role in arsenic transformations under combustion conditions.

A novel method to control hydrolytic degradation of nanocomposite biocompatible materials via imparting superhydrophobicity

Energy Technology Data Exchange (ETDEWEB)

Khakbaz, Mobina [Department of Chemical Engineering, Islamic Azad University, Shahrood Branch, P.O. Box 36155-163, Shahrood (Iran, Islamic Republic of); Hejazi, Iman [Department of Polymer Engineering & Color Technology, Amirkabir University of Technology, Tehran (Iran, Islamic Republic of); Seyfi, Javad, E-mail: Jseyfi@gmail.com [Department of Chemical Engineering, Islamic Azad University, Shahrood Branch, P.O. Box 36155-163, Shahrood (Iran, Islamic Republic of); Jafari, Seyed-Hassan [School of Chemical Engineering, University of Tehran, P.O. Box 11155-4563, Tehran (Iran, Islamic Republic of); Khonakdar, Hossein Ali [Iran Polymer and Petrochemical Institute, P.O. Box 14965/115, Tehran (Iran, Islamic Republic of); Davachi, Seyed Mohammad [School of Chemical Engineering, University of Tehran, P.O. Box 11155-4563, Tehran (Iran, Islamic Republic of)

2015-12-01

Highlights: • Superhydrophobic surface was obtained from a terpolymer for biomedical applications. • Hydrolytic degradation was delayed notably through inducing superhydrophobicity. • A novel method including combined use of non-solvent and nanoparticles was used. • Extreme wettabilities are attained by varying non-solvent and nanoparticles content. • Use of nanoparticle increased pore size via accelerating the evaporation process. - Abstract: Acceleration of hydrolytic degradation of biomedical materials is not always desirable. For instance, terpolymers based on L-lactide, glycolide and trimethylene carbonate exhibit very fast hydrolytic degradation due to their amorphous structure, hydrophilicity, and high water absorption capability. Therefore, an attempt was made in the current study to impede the hydrolytic degradation for these materials through imparting superhydrophobicity to their surfaces. The used terpolymer has been shown to have promising potential applications as bio-absorbable surgical sutures and other biomedical materials, and thus, its applicability could be further extended upon impeding its hydrolytic degradation. Moreover, a novel method including combined use of non-solvent and nanoparticles was utilized to achieve superhydrophobicity. Very diverse wettability results were obtained which were attributed to the obtained various morphologies according to scanning electron microscopy results. More importantly, a unique hierarchical morphology was found to be responsible for the observed water repellent behavior. X-ray photoelectron spectroscopy results revealed co-existence of nanosilica particles and terpolymer chains on the surface's top layer. Finally, it was found that the superhydrophobic sample exhibited a significantly impeded hydrolytic degradation as compared with the hydrophilic pure terpolymer which was attributed to the formation of air pockets on the surface's top layer.

A method to measure hydrolytic activity of adenosinetriphosphatases (ATPases.

Directory of Open Access Journals (Sweden)

Gianluca Bartolommei

Full Text Available The detection of small amounts (nanomoles of inorganic phosphate has a great interest in biochemistry. In particular, phosphate detection is useful to evaluate the rate of hydrolysis of phosphatases, that are enzymes able to remove phosphate from their substrate by hydrolytic cleavage. The hydrolysis rate is correlated to enzyme activity, an extremely important functional parameter. Among phosphatases there are the cation transporting adenosinetriphosphatases (ATPases, that produce inorganic phosphate by cleavage of the γ-phosphate of ATP. These membrane transporters have many fundamental physiological roles and are emerging as potential drug targets. ATPase hydrolytic activity is measured to test enzyme functionality, but it also provides useful information on possible inhibitory effects of molecules that interfere with the hydrolytic process. We have optimized a molybdenum-based protocol that makes use of potassium antimony (III oxide tartrate (originally employed for phosphate detection in environmental analysis to allow its use with phosphatase enzymes. In particular, the method was successfully applied to native and recombinant ATPases to demonstrate its reliability, validity, sensitivity and versatility. Our method introduces significant improvements to well-established experimental assays, which are currently employed for ATPase activity measurements. Therefore, it may be valuable in biochemical and biomedical investigations of ATPase enzymes, in combination with more specific tests, as well as in high throughput drug screening.

Evaluation of wild herbivore faeces from South Africa as a potential source of hydrolytically active microorganisms

CSIR Research Space (South Africa)

Ndlela, LL

2016-02-01

Full Text Available once hydrolysis (FDA) or reduction (TTC) occurred. The fluorescein diacetate assay operates on the princi- ple of hydrolytic release of two acetate groups via ester bond cleavage by free and membrane-bound hydrolytic enzymes, yielding the yellow... hydrolytic enzymes such as amylases can cleave its ester bonds as well (Lundgren 1981; Green et  al. 2006). The FDA hydrolysis assay has also been utilised and recommended as an efficient method to estimate active cells within environmental samples...

Effect of Chain-Extenders on the Properties and Hydrolytic Degradation Behavior of the Poly(lactide/ Poly(butylene adipate-co-terephthalate Blends

Directory of Open Access Journals (Sweden)

Mingqing Chen

2013-10-01

Full Text Available Biodegradable poly(lactide/poly(butylene adipate-co-terephthalate (PLA/PBAT blends were prepared by reactive blending in the presence of chain-extenders. Two chain-extenders with multi-epoxy groups were studied. The effect of chain-extenders on the morphology, mechanical properties, thermal behavior, and hydrolytic degradation of the blends was investigated. The compatibility between the PLA and PBAT was significantly improved by in situ formation of PLA-co-PBAT copolymers in the presence of the chain-extenders, results in an enhanced ductility of the blends, e.g., the elongation at break was increased to 500% without any decrease in the tensile strength. The differential scanning calorimeter (DSC results reveal that cold crystallization of PLA was enhanced due to heterogeneous nucleation effect of the in situ compatibilized PBAT domains. As known before, PLA is sensitive to hydrolysis and in the presence of PBAT and the chain-extenders, the hydrolytic degradation of the blend was evident. A three-stage hydrolysis mechanism for the system is proposed based on a study of weight loss and molecular weight reduction of the samples and the pH variation of the degradation medium.

Effect of Substrate Character on Heterogeneous Ozone Reaction Rate with Individual PAHs and Their Reaction Mixtures

Science.gov (United States)

Holmen, B. A.; Stevens, T.

2009-12-01

Vehicle exhaust contains many unregulated chemical compounds that are harmful to human health and the natural environment, including polycyclic aromatic hydrocarbons (PAH), a class of organic compounds derived from fuel combustion that can be carcinogenic and mutagenic. PAHs have been quantified in vehicle-derived ultrafine particles (Dpsolid, reacting the samples with gas-phase ozone, and determining both PAH loss over time and products formed, using thermal-desorption gas chromatography / mass spectrometry (TD-GC/MS). The individual PAHs anthracene, phenanthrene, and fluorene, adsorbed to a QFF were also separately reacted with 0.4 ppm ozone. A volatilization control and the collection of volatilized PAHs using a Tenax-packed thermal desorption vial completed the mass balance and aided determination parent-product relationships. Heterogeneous reaction products analyzed directly without derivatization indicate the formation of 9,10-anthracenedione, 9H-fluoren-9-one, and (1,1’-biphenyl)-2,2’-dicarboxaldehyde from the reaction of ozone with the PAH mix on a QFF, but only 9,10-anthracenedione was detected for the diesel PM reaction. The implications of these results for aging of diesel particulate in urban environments will be discussed.

Heterogeneous redox reactions in groundwater flow systems - Investigation and application of two different coupled codes

Energy Technology Data Exchange (ETDEWEB)

Pfingsten, W.; Carnahan, C.L. [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

1995-05-01

Two simulators of reactive chemical transport are applied to a set of problems involving heterogeneous reactions of uranium species. The simulators use similar algorithms to compute the heterogeneous chemical equilibria, but they use different approaches to the computation of solute transport and to the coupling of transport with chemical reactions. One simulator (MCOTAC) sequentially couples calculations of static chemical equilibria to a random-walk simulation of solute advection and dispersion. The other simulator (THCC) directly couples mass action relations for chemical equilibria to finite-difference representations of the solute transport equations. The aim of the comparison was to demonstrate the applicability of the newly developed code MCOTAC to redox problems, and to identify and investigate general differences between the two types of codes within these applications. The chosen heterogeneous redox systems are hypothetically generate systems which provide numerical difficulties within the coupled code calculation. Uranium, an important component of heterogeneous redox systems consisting of uraniferous solids and natural groundwaters, was chosen as a main component in the example redox systems because of practical interest for performance assessment of geological repositories for nuclear wastes. The calculations show reasonable agreement, in general, between the two computational approaches. Specific areas of disagreement arise from numerical difficulties to each approach. Such `benchmarking` can enhance confidence in the overall performance of individual simulators while identifying aspects that may require further investigations and possible modifications. (author) figs., tabs., 7 refs.

MRI of Heterogeneous Hydrogenation Reactions Using Parahydrogen Polarization

Energy Technology Data Exchange (ETDEWEB)

Burt, Scott Russell [Univ. of California, Berkeley, CA (United States)

2008-01-01

The power of magnetic resonance imaging (MRI) is its ability to image the internal structure of optically opaque samples and provide detailed maps of a variety of important parameters, such as density, diffusion, velocity and temperature. However, one of the fundamental limitations of this technique is its inherent low sensitivity. For example, the low signal to noise ratio (SNR) is particularly problematic for imaging gases in porous materials due to the low density of the gas and the large volume occluded by the porous material. This is unfortunate, as many industrially relevant chemical reactions take place at gas-surface interfaces in porous media, such as packed catalyst beds. Because of this severe SNR problem, many techniques have been developed to directly increase the signal strength. These techniques work by manipulating the nuclear spin populations to produce polarized} (i.e., non-equilibrium) states with resulting signal strengths that are orders of magnitude larger than those available at thermal equilibrium. This dissertation is concerned with an extension of a polarization technique based on the properties of parahydrogen. Specifically, I report on the novel use of heterogeneous catalysis to produce parahydrogen induced polarization and applications of this new technique to gas phase MRI and the characterization of micro-reactors. First, I provide an overview of nuclear magnetic resonance (NMR) and how parahydrogen is used to improve the SNR of the NMR signal. I then present experimental results demonstrating that it is possible to use heterogeneous catalysis to produce parahydrogen-induced polarization. These results are extended to imaging void spaces using a parahydrogen polarized gas. In the second half of this dissertation, I demonstrate the use of parahydrogen-polarized gas-phase MRI for characterizing catalytic microreactors. Specifically, I show how the improved SNR allows one to map parameters important for characterizing the heat and mass

Hydrolytic catalysis and structural stabilization in a designed metalloprotein

Science.gov (United States)

Zastrow, Melissa L.; Peacock, Anna F. A.; Stuckey, Jeanne A.; Pecoraro, Vincent L.

2011-01-01

Metal ions are an important part of many natural proteins, providing structural, catalytic and electron transfer functions. Reproducing these functions in a designed protein is the ultimate challenge to our understanding of them. Here, we present an artificial metallohydrolase, which has been shown by X-ray crystallography to contain two different metal ions – a Zn(II) ion which is important for catalytic activity and a Hg(II) ion which provides structural stability. This metallohydrolase displays catalytic activity that compares well with several characteristic reactions of natural enzymes. It catalyses p-nitrophenyl acetate hydrolysis (pNPA) to within ~100-fold of the efficiency of human carbonic anhydrase (CA)II and is at least 550-fold better than comparable synthetic complexes. Similarly, CO2 hydration occurs with an efficiency within ~500-fold of CAII. While histidine residues in the absence of Zn(II) exhibit pNPA hydrolysis, miniscule apopeptide activity is observed for CO2 hydration. The kinetic and structural analysis of this first de novo designed hydrolytic metalloenzyme uncovers necessary design features for future metalloenzymes containing one or more metals. PMID:22270627

Kinetics of contrail particles formation and heterogeneous reactions on such particles

Energy Technology Data Exchange (ETDEWEB)

Kogan, M.N.; Butkovsky, A.V.; Erofeev, A.I.; Freedlender, O.G.; Makashev, N.K. [Central Aerohydrodynamic Inst., Zhukovsky (Russian Federation)

1997-12-31

The research of impact of aircraft emissions upon the atmosphere is very complex and difficult problem. More than two decades of intensive investigations of the problem of ozone decay do not permit to make definite conclusions. Many important problems still remain unsolved in the aircraft/atmosphere interaction: engine, nozzle, jet, jet/vortex system interaction, vortex breakdown, contrail formation, meso-scale and global processes, their effects on climate. The particles formation and heterogeneous reactions play an important role in some of these processes. These problems are discussed. (author) 11 refs.

Kinetics of contrail particles formation and heterogeneous reactions on such particles

Energy Technology Data Exchange (ETDEWEB)

Kogan, M N; Butkovsky, A V; Erofeev, A I; Freedlender, O G; Makashev, N K [Central Aerohydrodynamic Inst., Zhukovsky (Russian Federation)

1998-12-31

The research of impact of aircraft emissions upon the atmosphere is very complex and difficult problem. More than two decades of intensive investigations of the problem of ozone decay do not permit to make definite conclusions. Many important problems still remain unsolved in the aircraft/atmosphere interaction: engine, nozzle, jet, jet/vortex system interaction, vortex breakdown, contrail formation, meso-scale and global processes, their effects on climate. The particles formation and heterogeneous reactions play an important role in some of these processes. These problems are discussed. (author) 11 refs.

Three dimensional radiative flow of magnetite-nanofluid with homogeneous-heterogeneous reactions

Science.gov (United States)

Hayat, Tasawar; Rashid, Madiha; Alsaedi, Ahmed

2018-03-01

Present communication deals with the effects of homogeneous-heterogeneous reactions in flow of nanofluid by non-linear stretching sheet. Water based nanofluid containing magnetite nanoparticles is considered. Non-linear radiation and non-uniform heat sink/source effects are examined. Non-linear differential systems are computed by Optimal homotopy analysis method (OHAM). Convergent solutions of nonlinear systems are established. The optimal data of auxiliary variables is obtained. Impact of several non-dimensional parameters for velocity components, temperature and concentration fields are examined. Graphs are plotted for analysis of surface drag force and heat transfer rate.

Insights into reaction mechanisms in heterogeneous catalysis revealed by in situ NMR spectroscopy.

Science.gov (United States)

Blasco, Teresa

2010-12-01

This tutorial review intends to show the possibilities of in situ solid state NMR spectroscopy in the elucidation of reaction mechanisms and the nature of the active sites in heterogeneous catalysis. After a brief overview of the more usual experimental devices used for in situ solid state NMR spectroscopy measurements, some examples of applications taken from the recent literature will be presented. It will be shown that in situ NMR spectroscopy allows: (i) the identification of stable intermediates and transient species using indirect methods, (ii) to prove shape selectivity in zeolites, (iii) the study of reaction kinetics, and (iv) the determination of the nature and the role played by the active sites in a catalytic reaction. The approaches and methodology used to get this information will be illustrated here summarizing the most relevant contributions on the investigation of the mechanisms of a series of reactions of industrial interest: aromatization of alkanes on bifunctional catalysts, carbonylation reaction of methanol with carbon monoxide, ethylbenzene disproportionation, and the Beckmann rearrangement reaction. Special attention is paid to the research carried out on the role played by carbenium ions and alkoxy as intermediate species in the transformation of hydrocarbon molecules on solid acid catalysts.

Light-induced nitrous acid (HONO) production from NO2 heterogeneous reactions on household chemicals

Science.gov (United States)

Gómez Alvarez, Elena; Sörgel, Matthias; Gligorovski, Sasho; Bassil, Sabina; Bartolomei, Vincent; Coulomb, Bruno; Zetzsch, Cornelius; Wortham, Henri

2014-10-01

Nitrous acid (HONO) can be generated in various indoor environments directly during combustion processes or indirectly via heterogeneous NO2 reactions with water adsorbed layers on diverse surfaces. Indoors not only the concentrations of NO2 are higher but the surface to volume (S/V) ratios are larger and therefore the potential of HONO production is significantly elevated compared to outdoors. It has been claimed that the UV solar light is largely attenuated indoors. Here, we show that solar light (λ > 340 nm) penetrates indoors and can influence the heterogeneous reactions of gas-phase NO2 with various household surfaces. The NO2 to HONO conversion mediated by light on surfaces covered with domestic chemicals has been determined at atmospherically relevant conditions i.e. 50 ppb NO2 and 50% RH. The formation rates of HONO were enhanced in presence of light for all the studied surfaces and are determined in the following order: 1.3·109 molecules cm-2 s-1 for borosilicate glass, 1.7·109 molecules cm-2 s-1 for bathroom cleaner, 1.0·1010 molecules cm-2 s-1 on alkaline detergent (floor cleaner), 1.3·1010 molecules cm-2 s-1 for white wall paint and 2.7·1010 molecules cm-2 s-1 for lacquer. These results highlight the potential of household chemicals, used for cleaning purposes to generate HONO indoors through light-enhanced NO2 heterogeneous reactions. The results obtained have been applied to predict the timely evolution of HONO in a real indoor environment using a dynamic mass balance model. A steady state mixing ratio of HONO has been estimated at 1.6 ppb assuming a contribution from glass, paint and lacquer and considering the photolysis of HONO as the most important loss process.

Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer

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Green, Christopher T.; Böhlke, John Karl; Bekins, Barbara A.; Phillips, Steven P.

2010-01-01

Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field‐scale (apparent) estimated reaction rates and isotopic fractionations and local‐scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and field observations were used to study the effects of physical heterogeneity on reaction parameter estimates. Field measurements included major ions, age tracers, stable isotopes, and dissolved gases. Parameters were estimated for the O2 reduction rate, denitrification rate, O2 threshold for denitrification, and stable N isotope fractionation during denitrification. For multiple geostatistical realizations of the aquifer, inverse modeling was used to establish reactive transport simulations that were consistent with field observations and served as a basis for numerical experiments to compare sample‐based estimates of “apparent” parameters with “true“ (intrinsic) values. For this aquifer, non‐Gaussian dispersion reduced the magnitudes of apparent reaction rates and isotope fractionations to a greater extent than Gaussian mixing alone. Apparent and true rate constants and fractionation parameters can differ by an order of magnitude or more, especially for samples subject to slow transport, long travel times, or rapid reactions. The effect of mixing on apparent N isotope fractionation potentially explains differences between previous laboratory and field estimates. Similarly, predicted effects on apparent O2threshold values for denitrification are consistent with previous reports of higher values in aquifers than in the laboratory. These results show that hydrogeological complexity substantially influences the interpretation and prediction of reactive transport.

Effect of Heterogeneous Chemical Reactions on the Köhler Activation of Aqueous Organic Aerosols.

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Djikaev, Yuri S; Ruckenstein, Eli

2018-05-03

We study some thermodynamic aspects of the activation of aqueous organic aerosols into cloud droplets considering the aerosols to consist of liquid solution of water and hydrophilic and hydrophobic organic compounds, taking into account the presence of reactive species in the air. The hydrophobic (surfactant) organic molecules on the surface of such an aerosol can be processed by chemical reactions with some atmospheric species; this affects the hygroscopicity of the aerosol and hence its ability to become a cloud droplet either via nucleation or via Köhler activation. The most probable pathway of such processing involves atmospheric hydroxyl radicals that abstract hydrogen atoms from hydrophobic organic molecules located on the aerosol surface (first step), the resulting radicals being quickly oxidized by ubiquitous atmospheric oxygen molecules to produce surface-bound peroxyl radicals (second step). These two reactions play a crucial role in the enhancement of the Köhler activation of the aerosol and its evolution into a cloud droplet. Taking them and a third reaction (next in the multistep chain of relevant heterogeneous reactions) into account, one can derive an explicit expression for the free energy of formation of a four-component aqueous droplet on a ternary aqueous organic aerosol as a function of four independent variables of state of a droplet. The results of numerical calculations suggest that the formation of cloud droplets on such (aqueous hydrophilic/hydrophobic organic) aerosols is most likely to occur as a Köhler activation-like process rather than via nucleation. The model allows one to determine the threshold parameters of the system necessary for the Köhler activation of such aerosols, which are predicted to be very sensitive to the equilibrium constant of the chain of three heterogeneous reactions involved in the chemical aging of aerosols.

Heterogeneous photocatalysis of real textile wastewater: evaluation of reaction kinetics and characterization.

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Sahoo, Chittaranjan; Gupta, Ashok K; Pillai, Indu M Sasidharan

2012-01-01

Real textile wastewater collected from the cotton dyeing bath of a fabric dyeing and finishing plant was subjected to heterogeneous photocatalysis using Ag(+) doped TiO(2) under UV irradiation in a batch reactor. The photocatalysts were characterized by FESEM, XRD, EDS, FTIR, DRS and BET analyses. The kinetics of the reaction was also evaluated. Colour removal was more than 88%, 94% and 99%, respectively for undiluted, 2 times diluted and 5 times diluted wastewater with Ag(+) doped TiO(2) (2.5 g/L) after UV irradiation for 360 minutes. The COD removal for undiluted, 2 times diluted and 5 times diluted wastewater was 47%, 70% and 92%, respectively under similar conditions. The reaction followed Langmuir-Hinshelwood pseudo first order kinetic model and the data fitted well to polynomial regression analysis.

The Hydrolytic Stability and Degradation Mechanism of a Hierarchically Porous Metal Alkylphosphonate Framework

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Kai Lv

2018-03-01

Full Text Available To aid the design of a hierarchically porous unconventional metal-phosphonate framework (HP-UMPF for practical radioanalytical separation, a systematic investigation of the hydrolytic stability of bulk phase against acidic corrosion has been carried out for an archetypical HP-UMPF. Bulk dissolution results suggest that aqueous acidity has a more paramount effect on incongruent leaching than the temperature, and the kinetic stability reaches equilibrium by way of an accumulation of a partial leached species on the corrosion conduits. A variation of particle morphology, hierarchical porosity and backbone composition upon corrosion reveals that they are hydrolytically resilient without suffering any great degradation of porous texture, although large aggregates crack into sporadic fractures while the nucleophilic attack of inorganic layers cause the leaching of tin and phosphorus. The remaining selectivity of these HP-UMPFs is dictated by a balance between the elimination of free phosphonate and the exposure of confined phosphonates, thus allowing a real-time tailor of radionuclide sequestration. Moreover, a plausible degradation mechanism has been proposed for the triple progressive dissolution of three-level hierarchical porous structures to elucidate resultant reactivity. These HP-UMPFs are compared with benchmark metal-organic frameworks (MOFs to obtain a rough grading of hydrolytic stability and two feasible approaches are suggested for enhancing their hydrolytic stability that are intended for real-life separation protocols.

Poly[(ethylene oxide)-co-(methylene ethylene oxide)]: A hydrolytically-degradable poly(ethylene oxide) platform

OpenAIRE

Lundberg, Pontus; Lee, Bongjae F.; van den Berg, Sebastiaan A.; Pressly, Eric D.; Lee, Annabelle; Hawker, Craig J.; Lynd, Nathaniel A.

2012-01-01

A facile method for imparting hydrolytic degradability to poly(ethylene oxide) (PEO), compatible with current PEGylation strategies, is presented. By incorporating methylene ethylene oxide (MEO) units into the parent PEO backbone, complete degradation was defined by the molar incorporation of MEO, and the structure of the degradation byproducts was consistent with an acid-catalyzed vinyl-ether hydrolysis mechanism. The hydrolytic degradation of poly[(ethylene oxide)-co-(methylene ethylene oxi...

On Cattaneo–Christov heat flux in MHD flow of Oldroyd-B fluid with homogeneous–heterogeneous reactions

International Nuclear Information System (INIS)

Hayat, Tasawar; Imtiaz, Maria; Alsaedi, Ahmed; Almezal, Saleh

2016-01-01

This paper investigates the steady two-dimensional magnetohydrodynamic (MHD) flow of an Oldroyd-B fluid over a stretching surface with homogeneous–heterogeneous reactions. Characteristics of relaxation time for heat flux are captured by employing new heat flux model proposed by Christov. A system of ordinary differential equations is obtained by using suitable transformations. Convergent series solutions are derived. Impacts of various pertinent parameters on the velocity, temperature and concentration are discussed. Analysis of the obtained results shows that fluid relaxation and retardation time constants have reverse behavior on the velocity and concentration fields. Also temperature distribution decreases for larger values of thermal relaxation time. - Highlights: • Cattaneo–Christov heat flux model is used to study the MHD flow of an Oldroyd-B fluid. • Velocity is decreasing function of Hartman number. • Increasing values of the strengths of homogeneous and heterogeneous reaction parameters decrease the wall concentration.

Exploring the Cattaneo-Christov heat flux phenomenon on a Maxwell-type nanofluid coexisting with homogeneous/heterogeneous reactions

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Sarkar, Amit; Kundu, Prabir Kumar

2017-12-01

This specific article unfolds the efficacy of Cattaneo-Christov heat flux on the heat and mass transport of Maxwell nanofluid flow over a stretched sheet with changeable thickness. Homogeneous/heterogeneous reactions in the fluid are additionally considered. The Cattaneo-Christov heat flux model is initiated in the energy equation. Appropriate similarity transformations are taken up to form a system of nonlinear ODEs. The impact of related parameters on the nanoparticle concentration and temperature is inspected through tables and diagrams. It is renowned that temperature distribution increases for lower values of the thermal relaxation parameter. The rate of mass transfer is enhanced for increasing in the heterogeneous reaction parameter but the reverse tendency is ensued for the homogeneous reaction parameter. On the other side, the rate of heat transfer is getting enhanced for the Cattaneo-Christov model compared to the classical Fourier's model for some flow factors. Thus the implication of the current study is to delve its unique effort towards the generalized version of traditional Fourier's law at nano level.

Preparation of hydrolytic liquid from dried distiller's grains with solubles and fumaric acid fermentation by Rhizopus arrhizus RH 7-13.

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Liu, Huan; Yue, Xuemin; Jin, Yuhan; Wang, Meng; Deng, Li; Wang, Fang; Tan, Tianwei

2017-10-01

Fumaric acid production from lignocellulosic materials is an alternative chemicals production system. This work investigated the suitable conditions for hydrolysis of dried distiller's grains with solubles (DDGS). The hydrolytic liquid was subsequently used for the production of fumaric acid. After optimizing the hydrolysis conditions, the most suitable concentration of H 2 SO 4 (2%), hydrolysis temperature (120 °C), hydrolysis time (100min) and solid/liquid ratio (1:10) were obtained. The yield of monosaccharides reached 258 mg/g DDGS and 15.88 g/L glucose, 7.53 g/L xylose and 2.35 g/L arabinose were obtained in unprocessed hydrolytic liquid. The furfural inhibitor in the hydrolytic liquid was also detected and the yield of it was reducing progressively in the pretreatment process. The ferment ability of the hydrolytic liquid from DDGS was tested through the process of fumaric acid production by Rhizopus arrhizus RH 7-13. The unprocessed hydrolytic liquid was not appropriate for the fermentation process. The yield of fumaric acid from the concentrated processed hydrolytic liquid reached 18.93 g/L, which was close to the yield of fermenting 80 g/L glucose. This result indicated that the commonly used carbon resource glucose could to some extent be replaced by processed hydrolytic liquid. Copyright © 2017 Elsevier Ltd. All rights reserved.

Sulfurized limonite as material for fast decomposition of organic compounds by heterogeneous Fenton reaction

International Nuclear Information System (INIS)

Toda, Kei; Tanaka, Toshinori; Tsuda, Yutaka; Ban, Masahiro; Koveke, Edwin P.; Koinuma, Michio; Ohira, Shin-Ichi

2014-01-01

Graphical abstract: - Highlights: • Used limonite degrades organic compounds by heterogeneous Fenton reaction. • Sulfurized limonite removes methylene blue color in seconds. • Recycled limonite can be used for biogas purification and wastewater treatment. - Abstract: Rapid decomposition of wastewater contaminants using sulfurized limonite (S-limonite) was investigated. Limonite is used for desulfurization of biogases, and S-limonite is obtained from desulfurization plants as solid waste. In this work, the profitable use of S-limonite in water treatment was examined. The divalent Fe in S-limonite was expected to produce OH radicals, as Fe 2+ ions and limonite thermally treated with H 2 do. Methylene blue was used for batch-wise monitoring of the decomposition performance. The decomposition rate was fast and the methylene blue solution color disappeared in only 10 s when a small amount of H 2 O 2 was added (1 mM in the sample solution) in the presence of S-limonite. The OH radicals were formed by a heterogeneous reaction on the S-limonite surface and Fenton reaction with dissolved Fe 2+ . The decomposition of pentachlorophenol was also examined; it was successfully decomposed in batch-wise tests. The surfaces of limonite before sulfurization, S-limonite, and S-limonite after use for water treatment were performed using scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that S-limonite reverted to limonite after being used for water treatment

Sulfurized limonite as material for fast decomposition of organic compounds by heterogeneous Fenton reaction

Energy Technology Data Exchange (ETDEWEB)

Toda, Kei, E-mail: todakei@sci.kumamoto-u.ac.jp [Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Tanaka, Toshinori; Tsuda, Yutaka; Ban, Masahiro; Koveke, Edwin P. [Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Koinuma, Michio [Department of Chemistry and Biochemistry, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan); Ohira, Shin-Ichi [Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555 (Japan)

2014-08-15

Graphical abstract: - Highlights: • Used limonite degrades organic compounds by heterogeneous Fenton reaction. • Sulfurized limonite removes methylene blue color in seconds. • Recycled limonite can be used for biogas purification and wastewater treatment. - Abstract: Rapid decomposition of wastewater contaminants using sulfurized limonite (S-limonite) was investigated. Limonite is used for desulfurization of biogases, and S-limonite is obtained from desulfurization plants as solid waste. In this work, the profitable use of S-limonite in water treatment was examined. The divalent Fe in S-limonite was expected to produce OH radicals, as Fe{sup 2+} ions and limonite thermally treated with H{sub 2} do. Methylene blue was used for batch-wise monitoring of the decomposition performance. The decomposition rate was fast and the methylene blue solution color disappeared in only 10 s when a small amount of H{sub 2}O{sub 2} was added (1 mM in the sample solution) in the presence of S-limonite. The OH radicals were formed by a heterogeneous reaction on the S-limonite surface and Fenton reaction with dissolved Fe{sup 2+}. The decomposition of pentachlorophenol was also examined; it was successfully decomposed in batch-wise tests. The surfaces of limonite before sulfurization, S-limonite, and S-limonite after use for water treatment were performed using scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that S-limonite reverted to limonite after being used for water treatment.

2-O-α-D-glucosylglycerol phosphorylase from Bacillus selenitireducens MLS10 possessing hydrolytic activity on β-D-glucose 1-phosphate.

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Takanori Nihira

Full Text Available The glycoside hydrolase family (GH 65 is a family of inverting phosphorylases that act on α-glucosides. A GH65 protein (Bsel_2816 from Bacillus selenitireducens MLS10 exhibited inorganic phosphate (Pi-dependent hydrolysis of kojibiose at the rate of 0.43 s(-1. No carbohydrate acted as acceptor for the reverse phosphorolysis using β-D-glucose 1-phosphate (βGlc1P as donor. During the search for a suitable acceptor, we found that Bsel_2816 possessed hydrolytic activity on βGlc1P with a k cat of 2.8 s(-1; moreover, such significant hydrolytic activity on sugar 1-phosphate had not been reported for any inverting phosphorylase. The H2 (18O incorporation experiment and the anomeric analysis during the hydrolysis of βGlc1P revealed that the hydrolysis was due to the glucosyl-transferring reaction to a water molecule and not a phosphatase-type reaction. Glycerol was found to be the best acceptor to generate 2-O-α-D-glucosylglycerol (GG at the rate of 180 s(-1. Bsel_2816 phosphorolyzed GG through sequential Bi-Bi mechanism with a k cat of 95 s(-1. We propose 2-O-α-D-glucopyranosylglycerol: phosphate β-D-glucosyltransferase as the systematic name and 2-O-α-D-glucosylglycerol phosphorylase as the short name for Bsel_2816. This is the first report describing a phosphorylase that utilizes polyols, and not carbohydrates, as suitable acceptor substrates.

Hydrolytic and ligninolytic enzyme activities in the Pb contaminated soil inoculated with litter-decomposing fungi.

Science.gov (United States)

Kähkönen, Mika A; Lankinen, Pauliina; Hatakka, Annele

2008-06-01

The impact of Pb contamination was tested to five hydrolytic (beta-glucosidase, beta-xylosidase, beta-cellobiosidase, alpha-glucosidase and sulphatase) and two ligninolytic (manganese peroxidase, MnP and laccase) enzyme activities in the humus layer in the forest soil. The ability of eight selected litter-degrading fungi to grow and produce extracellular enzymes in the heavily Pb (40 g Pb of kg ww soil(-1)) contaminated and non-contaminated soil in the non-sterile conditions was also studied. The Pb content in the test soil was close to that of the shooting range at Hälvälä (37 g Pb of kg ww soil(-1)) in Southern Finland. The fungi were Agaricus bisporus, Agrocybe praecox, Gymnopus peronatus, Gymnopilus sapineus, Mycena galericulata, Gymnopilus luteofolius, Stropharia aeruginosa and Stropharia rugosoannulata. The Pb contamination (40 g Pb of kg ww soil(-1)) was deleterious to all five studied hydrolytic enzyme activities after five weeks of incubation. All five hydrolytic enzyme activities were significantly higher in the soil than in the extract of the soil indicating that a considerable part of enzymes were particle bound in the soils. Hydrolytic enzyme activities were higher in the non-contaminated soil than in the Pb contaminated soil. Fungal inocula increased the hydrolytic enzyme activities beta-cellobiosidase and beta-glucosidase in non-contaminated soils. All five hydrolytic enzyme activities were similar with fungi and without fungi in the Pb contaminated soil. This was in line that Pb contamination (40 g Pb of kg ww soil(-1)) depressed the growth of all fungi compared to those grown without Pb in the soil. Laccase and MnP activities were low in both Pb contaminated and non-contaminated soil cultures. MnP activities were higher in soil cultures containing Pb than without Pb. Our results showed that Pb in the shooting ranges decreased fungal growth and microbial functioning in the soil.

(R,S)-2-chlorophenoxyl pyrazolides as novel substrates for improving lipase-catalyzed hydrolytic resolution.

Science.gov (United States)

Kao, Min-fang; Lu, Pei-yu; Kao, Jou-yan; Wang, Pei-yun; Wu, An-chi; Tsai, Shau-Wei

2012-01-01

The best reaction condition of Candida antartica lipase B as biocatalyst, 3-(2-pyridyl)pyrazole as leaving azole, and water-saturated methyl t-butyl ether as reaction medium at 45°C were first selected for performing the hydrolytic resolution of (R,S)-2-(4-chlorophenoxyl) azolides (1-4). In comparison with the kinetic resolution of (R,S)-2-phenylpropionyl 3-(2-pyridyl)pyrazolide or (R,S)-α-methoxyphenylacetyl 3-(2-pyridyl)pyrazolide at the same reaction condition, excellent enantioselectivity with more than two order-of-magnitudes higher activity for each enantiomer was obtained. The resolution was then extended to other (R,S)-3-(2-pyridyl)pyrazolides (5-7) containing 2-chloro, 3-chloro, or 2,4-dichloro substituent, giving good (E > 48) to excellent (E > 100) enantioselectivity. The thermodynamic analysis for 1, 2, and 4-7 demonstrates profound effects of the acyl or leaving moiety on varying enthalpic and entropic contributions to the difference of Gibbs free energies. A thorough kinetic analysis further indicates that on the basis of 6, the excellent enantiomeric ratio for 4 and 7 is due to the higher reactivity of (S)-4 and lower reactivity of (R)-7, respectively. Copyright © 2011 Wiley-Liss, Inc.

Organosulfate Formation through the Heterogeneous Reaction of Sulfur Dioxide with Unsaturated Compounds

Science.gov (United States)

George, C.; Passananti, M.; Kong, L.; Shang, J.; Perrier, S.; Jianmin, C.; Donaldson, D. J.

2016-12-01

The atmospheric formation of organosulfur derivatives through reaction with SO2 is generally mediated by oxidants such as O3, OH; recently we have proposed a direct reaction between SO2 and unsaturated compounds as another possible pathway for organosulfate formation in the troposphere. For the first time it was shown recently that a heterogeneous reaction between SO2 and oleic acid (OA; an unsaturated fatty acid) takes place and leads efficiently to the formation of organosulfur products. Here, we demonstrate that this reaction proceeds on various unsaturated compounds, and may therefore have a general environmental impact. We used different experimental strategies i.e., a coated flow tube (CFT), an aerosol flow tube (AFT) and a DRIFT (diffuse reflectance infrared Fourier transform) cell. The reaction products were analyzed by means of liquid chromatography coupled to a high resolution mass spectrometer (LC-HR-MS). We report indeed that SO2 reacts with large variety of C=C unsaturations and that even in the presence of ozone, SO2 reacts with OA leading to organosulfur products. A strong enhancement in product formation is observed under actinic illumination, increases the atmospheric significance of this chemical pathway. This is probably due to the chromophoric nature of the SO2 adduct with C=C bonds, and means that the contribution of this direct addition of SO2 could be in excess of 5%. The detection in atmospheric aerosols of organosulfur compounds with the same chemical formulae as the products identified here seems to confirm the importance of this reaction in the atmosphere.

Nondestructive evaluation of a new hydrolytically degradable and photo-clickable PEG hydrogel for cartilage tissue engineering.

Science.gov (United States)

Neumann, Alexander J; Quinn, Timothy; Bryant, Stephanie J

2016-07-15

Photopolymerizable and hydrolytically labile poly(ethylene glycol) (PEG) hydrogels formed from photo-clickable reactions were investigated as cell delivery platforms for cartilage tissue engineering (TE). PEG hydrogels were formed from thiol-norbornene PEG macromers whereby the crosslinks contained caprolactone segments with hydrolytically labile ester linkages. Juvenile bovine chondrocytes encapsulated in the hydrogels were cultured for up to four weeks and assessed biochemically and histologically, using standard destructive assays, and for mechanical and ultrasound properties, as nondestructive assays. Bulk degradation of acellular hydrogels was confirmed by a decrease in compressive modulus and an increase in mass swelling ratio over time. Chondrocytes deposited increasing amounts of sulfated glycosaminoglycans and collagens in the hydrogels with time. Spatially, collagen type II and aggrecan were present in the neotissue with formation of a territorial matrix beginning at day 21. Nondestructive measurements revealed an 8-fold increase in compressive modulus from days 7 to 28, which correlated with total collagen content. Ultrasound measurements revealed changes in the constructs over time, which differed from the mechanical properties, and appeared to correlate with ECM structure and organization shown by immunohistochemical analysis. Overall, non-destructive and destructive measurements show that this new hydrolytically degradable PEG hydrogel is promising for cartilage TE. Designing synthetic hydrogels whose degradation matches tissue growth is critical to maintaining mechanical integrity as the hydrogel degrades and new tissue forms, but is challenging due to the nature of the hydrogel crosslinks that inhibit diffusion of tissue matrix molecules. This study details a promising, new, photo-clickable and synthetic hydrogel whose degradation supports cartilaginous tissue matrix growth leading to the formation of a territorial matrix, concomitant with an

Canceling effect leads temperature insensitivity of hydrolytic enzymes in soil

Science.gov (United States)

Razavi, Bahar S.; Blagodatskaya, Evgenia; Kuzyakov, Yakov

2015-04-01

Extracellular enzymes are important for decomposition of many macromolecules abundant in soil such as cellulose, hemicelluloses and proteins (Allison et al., 2010; Chen et al., 2012). The temperature sensitivity of enzymes responsible for organic matter decomposition is the most crucial parameter for prediction of the effects of global warming on carbon cycle. Temperature responses of biological systems are often expressed as a Q10 functions; The Q10 describes how the rate of a chemical reaction changes with a temperature increase for 10 °C The aim of this study was to test how the canceling effect will change with variation in temperature interval, during short-term incubation. We additionally investigated, whether canceling effect occurs in a broad range of concentrations (low to high) and whether it is similar for the set of hydrolytic enzymes within broad range of temperatures. To this end, we performed soil incubation over a temperature range of 0-40°C (with 5°C steps). We determined the activities of three enzymes involved in plant residue decomposition: β-glucosidase and cellobiohydrolase, which are commonly measured as enzymes responsible for degrading cellulose (Chen et al., 2012), and xylanase, which degrades xylooligosaccharides (short xylene chain) in to xylose, thus being responsible for breaking down hemicelluloses (German et al., 2011). Michaelis-Menten kinetics measured at each temperature allowed to calculate Q10 values not only for the whole reaction rates, but specifically for maximal reaction rate (Vmax) and substrate affinity (Km). Subsequently, the canceling effect - simultaneous increase of Vmax and Km with temperature was analyzed within 10 and 5 degree of temperature increase. Three temperature ranges (below 10, between 15 and 25, and above 30 °C) clearly showed non-linear but stepwise increase of temperature sensitivity of all three enzymes and allowed to conclude for predominance of psychrophilic, mesophilic and thermophilic

Durability of switchable QR code carriers under hydrolytic and photolytic conditions

International Nuclear Information System (INIS)

Ecker, Melanie; Pretsch, Thorsten

2013-01-01

Following a guest diffusion approach, the surface of a shape memory poly(ester urethane) (PEU) was either black or blue colored. Bowtie-shaped quick response (QR) code carriers were then obtained from laser engraving and cutting, before thermo-mechanical functionalization (programming) was applied to stabilize the PEU in a thermo-responsive (switchable) state. The stability of the dye within the polymer surface and long-term functionality of the polymer were investigated against UVA and hydrolytic ageing. Spectrophotometric investigations verified UVA ageing-related color shifts from black to yellow-brownish and blue to petrol-greenish whereas hydrolytically aged samples changed from black to greenish and blue to light blue. In the case of UVA ageing, color changes were accompanied by dye decolorization, whereas hydrolytic ageing led to contrast declines due to dye diffusion. The Michelson contrast could be identified as an effective tool to follow ageing-related contrast changes between surface-dyed and laser-ablated (undyed) polymer regions. As soon as the Michelson contrast fell below a crucial value of 0.1 due to ageing, the QR code was no longer decipherable with a scanning device. Remarkably, the PEU information carrier base material could even then be adequately fixed and recovered. Hence, the surface contrast turned out to be the decisive parameter for QR code carrier applicability. (paper)

Durability of switchable QR code carriers under hydrolytic and photolytic conditions

Science.gov (United States)

Ecker, Melanie; Pretsch, Thorsten

2013-09-01

Following a guest diffusion approach, the surface of a shape memory poly(ester urethane) (PEU) was either black or blue colored. Bowtie-shaped quick response (QR) code carriers were then obtained from laser engraving and cutting, before thermo-mechanical functionalization (programming) was applied to stabilize the PEU in a thermo-responsive (switchable) state. The stability of the dye within the polymer surface and long-term functionality of the polymer were investigated against UVA and hydrolytic ageing. Spectrophotometric investigations verified UVA ageing-related color shifts from black to yellow-brownish and blue to petrol-greenish whereas hydrolytically aged samples changed from black to greenish and blue to light blue. In the case of UVA ageing, color changes were accompanied by dye decolorization, whereas hydrolytic ageing led to contrast declines due to dye diffusion. The Michelson contrast could be identified as an effective tool to follow ageing-related contrast changes between surface-dyed and laser-ablated (undyed) polymer regions. As soon as the Michelson contrast fell below a crucial value of 0.1 due to ageing, the QR code was no longer decipherable with a scanning device. Remarkably, the PEU information carrier base material could even then be adequately fixed and recovered. Hence, the surface contrast turned out to be the decisive parameter for QR code carrier applicability.

Accounting for the Decreasing Reaction Potential of Heterogeneous Aquifers in a Stochastic Framework of Aquifer-Scale Reactive Transport

Science.gov (United States)

Loschko, Matthias; Wöhling, Thomas; Rudolph, David L.; Cirpka, Olaf A.

2018-01-01

Many groundwater contaminants react with components of the aquifer matrix, causing a depletion of the aquifer's reactivity with time. We discuss conceptual simplifications of reactive transport that allow the implementation of a decreasing reaction potential in reactive-transport simulations in chemically and hydraulically heterogeneous aquifers without relying on a fully explicit description. We replace spatial coordinates by travel-times and use the concept of relative reactivity, which represents the reaction-partner supply from the matrix relative to a reference. Microorganisms facilitating the reactions are not explicitly modeled. Solute mixing is neglected. Streamlines, obtained by particle tracking, are discretized in travel-time increments with variable content of reaction partners in the matrix. As exemplary reactive system, we consider aerobic respiration and denitrification with simplified reaction equations: Dissolved oxygen undergoes conditional zero-order decay, nitrate follows first-order decay, which is inhibited in the presence of dissolved oxygen. Both reactions deplete the bioavailable organic carbon of the matrix, which in turn determines the relative reactivity. These simplifications reduce the computational effort, facilitating stochastic simulations of reactive transport on the aquifer scale. In a one-dimensional test case with a more detailed description of the reactions, we derive a potential relationship between the bioavailable organic-carbon content and the relative reactivity. In a three-dimensional steady-state test case, we use the simplified model to calculate the decreasing denitrification potential of an artificial aquifer over 200 years in an ensemble of 200 members. We demonstrate that the uncertainty in predicting the nitrate breakthrough in a heterogeneous aquifer decreases with increasing scale of observation.

Effect of Coatings on the Uptake Rate and HONO Yield in Heterogeneous Reaction of Soot with NO2

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Cruz-Quiñones, M.; Khalizov, A. F.; Zhang, R.

2009-12-01

Heterogeneous reaction of nitrogen dioxide on carbon soot aerosols has been suggested as a possible source of nighttime nitrous acid (HONO) in atmosphere boundary layer. Available laboratory data show significant variability in the measured reaction probabilities and HONO yields, making it difficult to asses the atmospheric significance of this process. Moreover, little is known of how aging of soot aerosol through internal mixing with other atmospheric trace constituents will affect the heterogeneous reactivity and HONO production. In this work, the heterogeneous reaction of NO2 on fresh and aged soot films leading to HONO formation was studied through a series of kinetic uptake experiments and HONO yield measurements. Soot samples were prepared by incomplete combustion of propane and kerosene fuels under lean and rich flame conditions. Experiments were performed in a low-pressure, fast-flow reactor coupled to a chemical ionization mass spectrometer (CIMS), using atmospheric-level NO2 concentrations. Heterogeneous uptake coefficients, γ(geom) and γ(BET), were calculated using geometric and internal BET soot surface areas, respectively. The uptake coefficient and the HONO yield depend on the type of fuel and combustion regime and are the highest for soot samples prepared using rich kerosene flame. Although, the internal surface area of soot measured by BET method is a factor of 50 to 500 larger than the geometric surface area, only the top soot layers are involved in heterogeneous reaction with NO2 as follows from the observed weak dependence of γ(geom) and decrease in γ(BET) with increasing sample mass. Heating the soot samples before exposure to NO2 increases the BET surface area, the HONO yield, and the NO2 uptake coefficient due to the removal of the organic fraction from the soot backbone that unblocks active sites and makes them accessible for physical adsorption and chemical reactions. Our results support the oxidation-reduction mechanism involving

Extent of reaction in open systems with multiple heterogeneous reactions

Science.gov (United States)

Friedly, John C.

1991-01-01

The familiar batch concept of extent of reaction is reexamined for systems of reactions occurring in open systems. Because species concentrations change as a result of transport processes as well as reactions in open systems, the extent of reaction has been less useful in practice in these applications. It is shown that by defining the extent of the equivalent batch reaction and a second contribution to the extent of reaction due to the transport processes, it is possible to treat the description of the dynamics of flow through porous media accompanied by many chemical reactions in a uniform, concise manner. This approach tends to isolate the reaction terms among themselves and away from the model partial differential equations, thereby enabling treatment of large problems involving both equilibrium and kinetically controlled reactions. Implications on the number of coupled partial differential equations necessary to be solved and on numerical algorithms for solving such problems are discussed. Examples provided illustrate the theory applied to solute transport in groundwater flow.

A Monte Carlo simulation of the exchange reaction between gaseous molecules and the atoms on a heterogeneous solid surface

International Nuclear Information System (INIS)

Imai, Hisao

1980-01-01

A method of the Monte Carlo simulation of the isotopic exchange reaction between gaseous molecules and the atoms on an arbitrarily heterogeneous solid surface is described by employing hydrogen as an example. (author)

Impacts of heterogeneous reactions to atmospheric peroxides: Observations and budget analysis study

Science.gov (United States)

Qin, Mengru; Chen, Zhongming; Shen, Hengqing; Li, Huan; Wu, Huihui; Wang, Yin

2018-06-01

Atmospheric peroxides play important roles in atmospheric chemistry, acting as reactive oxidants and reservoirs of HOX and ROX radicals. Field measurements of atmospheric peroxides were conducted over urban Beijing from 2015 to 2016, including dust storm days, haze days and different seasons. We employed a box model based on RACM2 mechanism to conduct concentration simulation and budget analysis of hydrogen peroxide (H2O2) and peroxyacetic acid (PAA). In this study, heterogeneous reaction is found to be a significant sink for atmospheric H2O2 and PAA in urban Beijing. Here, we recommend a suitable uptake coefficient formula considering the water effect for model research of peroxides. It is found that H2O2 and PAA unexpectedly maintained considerable concentrations on haze days, even higher than that on non-haze days. This phenomenon is mainly ascribed to relatively high levels of volatile organic compounds and ozone on haze days. In addition, high levels of water vapor in pollution episode can promote not only the heterogeneous uptake to aerosol phase but also the production of H2O2. Atmospheric PAA formation is suggested to be sensitive to alkenes and NOX in urban Beijing. In particular, with the help of peroxides, sulfate formation rate from heterogeneous uptake could increase by ∼4 times on haze days, indicating the potential effect of peroxides on enhancement of aerosol oxidative property and secondary sulfate formation.

Substrate-Wrapped, Single-Walled Carbon Nanotube Probes for Hydrolytic Enzyme Characterization.

Science.gov (United States)

Kallmyer, Nathaniel E; Musielewicz, Joseph; Sutter, Joel; Reuel, Nigel F

2018-04-17

Hydrolytic enzymes are a topic of continual study and improvement due to their industrial impact and biological implications; however, the ability to measure the activity of these enzymes, especially in high-throughput assays, is limited to an established, few enzymes and often involves the measurement of secondary byproducts or the design of a complex degradation probe. Herein, a versatile single-walled carbon nanotube (SWNT)-based biosensor that is straightforward to produce and measure is described. The hydrolytic enzyme substrate is rendered as an amphiphilic polymer, which is then used to solubilize the hydrophobic nanotubes. When the target enzyme degrades the wrapping, the SWNT fluorescent signal is quenched due to increased solvent accessibility and aggregation, allowing quantitative measurement of hydrolytic enzyme activity. Using (6,5) chiral SWNT suspended with polypeptides and polysaccharides, turnover frequencies are estimated for cellulase, pectinase, and bacterial protease. Responses are recorded for concentrations as low as 5 fM using a well-characterized protease, Proteinase K. An established trypsin-based plate reader assay is used to compare this nanotube probe assay with standard techniques. Furthermore, the effect of freeze-thaw cycles and elevated temperature on enzyme activity is measured, suggesting freezing to have minimal impact even after 10 cycles and heating to be detrimental above 60 °C. Finally, rapid optimization of enzyme operating conditions is demonstrated by generating a response surface of cellulase activity with respect to temperature and pH to determine optimal conditions within 2 h of serial scans.

Advances in hexitol and ethylene glycol production by one-pot hydrolytic hydrogenation and hydrogenolysis of cellulose

International Nuclear Information System (INIS)

Li, Yuping; Liao, Yuhe; Cao, Xiaofeng; Wang, Tiejun; Ma, Longlong; Long, Jinxing; Liu, Qiying; Xua, Ying

2015-01-01

In this review, recent advances in the one-pot hydrolytic hydrogenation and hydrogenolysis of cellulose to value-added polyols, including hexitols (sorbitol, mannitol, and isosorbide) and 1,2-alkanediols (ethylene glycol and 1,2-propylene glycol), are summarized. Methods for the generation of H + in the first step of cellulose hydrolysis to form intermediate sugars, such as the use of soluble acids (mineral acids and heteropoly acids) and H + produced in situ from functional supports and H 2 dissociation, are classified and analyzed, considering its combination with active metals for the subsequent hydrogenation or hydrogenolysis of sugars to polyols. The interaction of non-noble metals such as nickel, bimetals, and tungsten with support materials in the catalytic conversion of intermediate sugars to hexitols and ethylene glycol is reviewed. The corresponding reaction pathways and mechanisms are discussed, including the conversion process using basic supports and solution conditions. Major challenges and promising routes are also suggested for the future development of the chemocatalytic conversion of cellulose. - Highlights: • Advances in the one-pot hydrolytic hydrogenation/hydrogenolysis of cellulose are summarized. • The interaction of non-noble metals with support materials for cellulose conversion is reviewed. • Method for the generation of in situ H + and effects of the acidic groups on supports are discussed. • Incomplete identification of intermediates/products causes mechanism complications. • Efficient conversion, separation and purification are other concerns for cellulose degrading

Kinetics of Heterogeneous Reaction of Sulfur Dioxide on Authentic Mineral Dust: Effects of Relative Humidity and Hydrogen Peroxide.

Science.gov (United States)

Huang, Liubin; Zhao, Yue; Li, Huan; Chen, Zhongming

2015-09-15

Heterogeneous reaction of SO2 on mineral dust seems to be an important sink for SO2. However, kinetic data about this reaction on authentic mineral dust are scarce and are mainly limited to low relative humidity (RH) conditions. In addition, little is known about the role of hydrogen peroxide (H2O2) in this reaction. Here, we investigated the uptake kinetics of SO2 on three authentic mineral dusts (i.e., Asian mineral dust (AMD), Tengger desert dust (TDD), and Arizona test dust (ATD)) in the absence and presence of H2O2 at different RHs using a filter-based flow reactor, and applied a parameter (effectiveness factor) to the estimation of the effective surface area of particles for the calculation of the corrected uptake coefficient (γc). We found that with increasing RH, the γc decreases on AMD particles, but increases on ATD and TDD particles. This discrepancy is probably due to the different mineralogy compositions and aging extents of these dust samples. Furthermore, the presence of H2O2 can promote the uptake of SO2 on mineral dust at different RHs. The probable explanations are that H2O2 rapidly reacts with SO2 on mineral dust in the presence of adsorbed water, and OH radicals, which can be produced from the heterogeneous decomposition of H2O2 on the mineral dust, immediately react with adsorbed SO2 as well. Our results suggest that the removal of SO2 via the heterogeneous reaction on mineral dust is an important sink for SO2 and has the potential to alter the physicochemical properties (e.g., ice nucleation ability) of mineral dust particles in the atmosphere.

Numerical study for Darcy-Forchheimer flow due to a curved stretching surface with Cattaneo-Christov heat flux and homogeneous-heterogeneous reactions

Directory of Open Access Journals (Sweden)

Tasawar Hayat

Full Text Available The current investigation presents Darcy-Forchheimer flow of viscous fluid caused by a curved stretching sheet. Flow for porous space is characterized by Darcy-Forchheimer relation. Concept of homogeneous and heterogeneous reactions is also utilized. Heat transfer for Cattaneo–Christov theory characterizing the feature of thermal relaxation is incorporated. Nonlinear differential systems are derived. Shooting algorithm is employed to construct the solutions for the resulting nonlinear system. The characteristics of various sundry parameters are studied and discussed. Skin friction coefficient and heat transfer rate are numerically described. Keywords: 2D flow, Curved stretching surface, Darcy-Forchheimer porous medium, Cattaneo-Christov heat flux, Homogeneous-heterogeneous reactions

Metal-ion complexes of functionalised 1,10-Phenanthrolines as hydrolytic synzymes

NARCIS (Netherlands)

Weijnen, J.G.J.

1993-01-01

In this thesis metal-ion complexes of functionalised 1,10-phenanthroline derivatives have been studied as model systems for hydrolytic metallo-enzymes. Amphiphilic metallo- complexes incorporated into micelles or vesicles and water-soluble complexes in pure aqueous buffer solutions, have

Nitric oxide reduction in coal combustion: role of char surface complexes in heterogeneous reactions.

Science.gov (United States)

Arenillas, Ana; Rubiera, Fernando; Pis, José J

2002-12-15

Nitrogen oxides are one of the major environmental problems arising from fossil fuel combustion. Coal char is relatively rich in nitrogen, and so this is an important source of nitrogen oxides during coal combustion. However, due to its carbonaceous nature, char can also reduce NO through heterogeneous reduction. The objectives of this work were on one hand to compare NO emissions from coal combustion in two different types of equipment and on the other hand to study the influence of char surface chemistry on NO reduction. A series of combustion tests were carried out in two different scale devices: a thermogravimetric analyzer coupled to a mass spectrometer and an FTIR (TG-MS-FTIR) and a fluidized bed reactor with an on line battery of analyzers. The TG-MS-FTIR system was also used to perform a specific study on NO heterogeneous reduction reactions using chars with different surface chemistry. According to the results obtained, it can be said that the TG-MS-FTIR system provides valuable information about NO heterogeneous reduction and it can give good trends of the behavior in other combustion equipments (i.e., fluidized bed combustors). It has been also pointed out that NO-char interaction depends to a large extent on temperature. In the low-temperature range (800 degrees C), a different mechanism is involved in NO heterogeneous reduction, the nature of the carbon matrix being a key factor.

Numerical tackling for viscoelastic fluid flow in rotating frame considering homogeneous-heterogeneous reactions

Directory of Open Access Journals (Sweden)

Najwa Maqsood

Full Text Available This study provides a numerical treatment for rotating flow of viscoelastic (Maxwell fluid bounded by a linearly deforming elastic surface. Mass transfer analysis is carried out in the existence of homogeneous-heterogeneous reactions. By means of usual transformation, the governing equations are changed into global similarity equations which have been tackled by an expedient shooting approach. A contemporary numerical routine bvp4c of software MATLAB is also opted to develop numerical approximations. Both methods of solution are found in complete agreement in all the cases. Velocity and concentration profiles are computed and elucidated for certain range of viscoelastic fluid parameter. The solutions contain a rotation-strength parameter λ that has a considerable impact on the flow fields. For sufficiently large value of λ, the velocity fields are oscillatory decaying function of the non-dimensional vertical distance. Concentration distribution at the surface is found to decrease upon increasing the strengths of chemical reactions. A comparison of present computations is made with those of already published ones and such comparison appears convincing. Keywords: Maxwell fluid, Similarity solution, Numerical method, Chemical reaction, Stretching sheet

A coupling alternative to reactive transport simulations for long-term prediction of chemical reactions in heterogeneous CO2 storage systems

Directory of Open Access Journals (Sweden)

M. De Lucia

2015-02-01

Full Text Available Fully coupled, multi-phase reactive transport simulations of CO2 storage systems can be approximated by a simplified one-way coupling of hydrodynamics and reactive chemistry. The main characteristics of such systems, and hypotheses underlying the proposed alternative coupling, are (i that the presence of CO2 is the only driving force for chemical reactions and (ii that its migration in the reservoir is only marginally affected by immobilisation due to chemical reactions. In the simplified coupling, the exposure time to CO2 of each element of the hydrodynamic grid is estimated by non-reactive simulations and the reaction path of one single batch geochemical model is applied to each grid element during its exposure time. In heterogeneous settings, analytical scaling relationships provide the dependency of velocity and amount of reactions to porosity and gas saturation. The analysis of TOUGHREACT fully coupled reactive transport simulations of CO2 injection in saline aquifer, inspired to the Ketzin pilot site (Germany, both in homogeneous and heterogeneous settings, confirms that the reaction paths predicted by fully coupled simulations in every element of the grid show a high degree of self-similarity. A threshold value for the minimum concentration of dissolved CO2 considered chemically active is shown to mitigate the effects of the discrepancy between dissolved CO2 migration in non-reactive and fully coupled simulations. In real life, the optimal threshold value is unknown and has to be estimated, e.g. by means of 1-D or 2-D simulations, resulting in an uncertainty ultimately due to the process de-coupling. However, such uncertainty is more than acceptable given that the alternative coupling enables using grids of the order of millions of elements, profiting from much better description of heterogeneous reservoirs at a fraction of the calculation time of fully coupled models.

Cirrus cloud mimic surfaces in the laboratory: organic acids, bases and NOx heterogeneous reactions

Science.gov (United States)

Sodeau, J.; Oriordan, B.

2003-04-01

CIRRUS CLOUD MIMIC SURFACES IN THE LABORATORY:ORGANIC ACIDS, BASES AND NOX HETEROGENEOUS REACTIONS. B. ORiordan, J. Sodeau Department of Chemistry and Environment Research Institute, University College Cork, Ireland j.sodeau@ucc.ie /Fax: +353-21-4902680 There are a variety of biogenic and anthropogenic sources for the simple carboxylic acids to be found in the troposphere giving rise to levels as high as 45 ppb in certain urban areas. In this regard it is of note that ants of genus Formica produce some 10Tg of formic acid each year; some ten times that produced by industry. The expected sinks are those generally associated with tropospheric chemistry: the major routes studied, to date, being wet and dry deposition. No studies have been carried out hitherto on the role of water-ice surfaces in the atmospheric chemistry of carboxylic acids and the purpose of this paper is to indicate their potential function in the heterogeneous release of atmospheric species such as HONO. The deposition of formic acid on a water-ice surface was studied using FT-RAIR spectroscopy over a range of temperatures between 100 and 165K. In all cases ionization to the formate (and oxonium) ions was observed. The results were confirmed by TPD (Temperature Programmed Desorption) measurements, which indicated that two distinct surface species adsorb to the ice. Potential reactions between the formic acid/formate ion surface and nitrogen dioxide were subsequently investigated by FT-RAIRS. Co-deposition experiments showed that N2O3 and the NO+ ion (associated with water) were formed as products. A mechanism is proposed to explain these results, which involves direct reaction between the organic acid and nitrogen dioxide. Similar experiments involving acetic acid also indicate ionization on a water-ice surface. The results are put into the context of atmospheric chemistry potentially occuring on cirrus cloud surfaces.

Products and kinetics of the heterogeneous reaction of suspended vinclozolin particles with ozone.

Science.gov (United States)

Gan, Jie; Yang, Bo; Zhang, Yang; Shu, Xi; Liu, Changgeng; Shu, Jinian

2010-11-25

Vinclozolin is a widely used fungicide that can be released into the atmosphere via application and volatilization. This paper reports an experimental investigation on the heterogeneous ozonation of vinclozolin particles. The ozonation of vinclozolin adsorbed on azelaic acid particles under pseudo-first-order conditions is investigated online with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). The ozonation products are analyzed with a combination of VUV-ATOFMS and GC/MS. Two main ozonation products are observed. The formation of the ozonation products results from addition of O(3) on the C-C double bond of the vinyl group. The heterogeneous reactive rate constant of vinclozolin particles under room temperature is (2.4 ± 0.4) × 10(-17) cm(3) molecules(-1) s(-1), with a corresponding lifetime at 100 ppbv O(3) of 4.3 ± 0.7 h, which is almost comparable with the estimated lifetime due to the reaction with atmospheric OH radicals (∼1.7 h). The reactive uptake coefficient for O(3) on vinclozolin particles is (6.1 ± 1.0) × 10(-4).

Hydrolytic Degradation Behaviors of Poly(p-dioxanone) in Ambient Environments

Institute of Scientific and Technical Information of China (English)

You Yuan; Song-dong Ding; Yin-qiao Zhao; Yu-zhong Wang

2014-01-01

The effects of temperature and relative humidity on the hydrolytic degradation of poly(p-dioxanone) (PPDO) were investigated.The hydrolytic degradation behaviors were monitored by tracing the changes of water absorption,mechanical and crystalline properties,molecular weight and its distribution,surface morphologies,as well as infrared absorption peaks and hydrogen chemical shifts during the degradation.It is found that the water absorption increases whilst the intrinsic viscosity,tensile strength and elongation at break decrease as the temperature or relative humidity increases.With degradation time growing,the molecular weight drops and its distribution broadens.The crystallinity of PPDO has a tendency to increase at first and then to decrease,while the crystalline structure is not significantly changed.At the same time,some cracks are observed on the surface and keep growing and deepening.All results show that temperature plays more significant roles than relative humidity during the degradation.The analyses of Fourier transform infrared spectroscopy and hydrogen nuclear magnetic resonance spectroscopy reveal that the degradation of PPDO is a predominant hydrolysis of ester linkages.

Molecular Imaging of Hydrolytic Enzymes Using PET and SPECT

OpenAIRE

Rempel, Brian P.; Price, Eric W.; Phenix, Christopher P.

2017-01-01

Hydrolytic enzymes are a large class of biological catalysts that play a vital role in a plethora of critical biochemical processes required to maintain human health. However, the expression and/or activity of these important enzymes can change in many different diseases and therefore represent exciting targets for the development of positron emission tomography (PET) and single-photon emission computed tomography (SPECT) radiotracers. This review focuses on recently reported radiolabeled sub...

Reaction kinetics for preparation of silica film with Stoeber method

International Nuclear Information System (INIS)

Shang Mengying; Jiang Xiaodong; Liu Miao; Luo Xuan; Tang Yongjian; Cao Linhong

2013-01-01

A new formula was proposed to investigate the relationship between reaction time and tetraethylorthosilicate (TEOS) conversion rate for preparation of silica sol with Stöber method, by studying the reaction kinetics of TEOS hydrolytic process. An appropriate conversion rate was then determined and used to calculate the theoretical optimal reaction time. Meanwhile, silica sols were prepared by sol-gel process using TEOS as precursor and ammonia as catalyst. It was found that the reaction time decreases with an increasing amount of ammonia and water. The values of experimental optimal reaction time were obtained, and agree with the theoretical results (the errors are within 5%), which shows good applicability of our formula. (authors)

The role of high temperature heterogeneous reaction kinetics in the rate of radionuclide vaporisation during core-concrete interactions

International Nuclear Information System (INIS)

Raymond, D.P.; Clough, P.N.

1989-09-01

Heterogeneous reactions may cause enhanced release of radionuclides during the core-concrete interaction (CCl) stage of a PWR severe accident. The VANESA computer code models these CCI releases using chemical equilibrium assumptions; however, the possibility that chemical kinetics could prevent equilibrium from being achieved is considered in this report. Direct experimental evidence is lacking on these reactions. Therefore, some analogues studies are reviewed, including examples of Eyring's surface reaction rate theory; sequential vaporisation-oxidation processes; iron and steelmaking chemistry; radionuclide evaporation from solid UO 2 . This circumstantial evidence appeared to agree with the current assumptions, in VANESA and some UK modelling studies, that mass transfer, rather than chemical kinetics will limit the rate at which equilibrium is attained. (author)

Reduction and Analysis of Low Temperature Shift Heterogeneous Catalyst for Water Gas Reaction in Ammonia Production

Directory of Open Access Journals (Sweden)

Zečević, N.

2013-09-01

Full Text Available In order to obtain additional quantities of hydrogen after the reforming reactions of natural gas and protect the ammonia synthesis catalyst, it is crucial to achieve and maintain maximum possible activity, selectivity and stability of the low temperature shift catalyst for conversion of water gas reaction during its lifetime. Whereas the heterogeneous catalyst comes in oxidized form, it is of the utmost importance to conduct the reduction procedure properly. The proper reduction procedure and continuous analysis of its performance would ensure the required activity, selectivity and stability throughout the catalyst’s service time. For the proper reduction procedure ofthe low temperature shift catalyst, in addition to process equipment, also necessary is a reliable and realistic system for temperature measurements, which will be effective for monitoring the exothermal temperature curves through all catalyst bed layers. For efficiency evaluation of low shift temperature catalyst reduction and its optimization, it is necessary to determine at regular time intervals the temperature approach to equilibrium and temperature profiles of individual layers by means of "S" and "die off" temperature exothermal curves. Based on the obtained data, the optimum inlet temperature could be determined, in order to maximally extend the service life of the heterogeneous catalyst as much as possible, and achieve the optimum equilibrium for conversion of the water gas. This paper presents the methodology for in situ reduction of the low temperature shift heterogeneous catalyst and the developed system for monitoring its individual layers to achieve the minimum possible content of carbon monoxide at the exit of the reactor. The developed system for temperature monitoring through heterogeneous catalyst layers provides the proper procedure for reduction and adjustment of optimum process working conditions for the catalyst by the continuous increase of reactor inlet

Scanning electron microscopic study of the hydrolytic degradation of poly(glycolic acid) suture

International Nuclear Information System (INIS)

Chu, C.C.; Campbell, N.D.

1982-01-01

This article reports the morphological observations on the surface changes of poly-(glycolic acid) sutures which have been exposed to various dosages of gamma irradiation (0, 2.5, 5.0, 10, 20 and 40 Mrad) and duration of immersion (0, 7, 14, 28, 48, 60, and 90 days) in a physiological saline buffer. The most important gross morphological characteristics of PGA suture hydrolytic degradation is the formation of surface cracks on the filaments. The regularity of the surface cracks increased with an increase in the gamma irradiation and the duration of hydrolysis. Surface cracks were not observed in irradiated sutures that had not been subjected to hydrolytic degradation. The arrangement of the surface cracks, their orientation on the filaments, and the direction of crack propagation provide very useful information for depicting the mechanism of hydrolytic degradation in this class of fibrous material. The microfibrillar model of fiber structure has been used as the basis for the proposed degradation mechanism of PGA in vitro. It is believed that hydrolysis occurs initially in the amorphous regions sandwiched between two crystalline zones, as tie-chain segments, free chain ends, and chain folds in these regions degrade into fragments. As degradation proceeds, the size of the fragments reaches the stage at which they can be dissolved into the buffer medium. This dissolution removes the fragments from the amorphous regions, and surface cracks appeared

Hydrolytically stable titanium-45

DEFF Research Database (Denmark)

Severin, Gregory; Fonslet, Jesper; Zhuravlev, Fedor

2014-01-01

metal-based chemotherapeutics such as cisplatin. The aim of our work has been to produce the radioactive analogue of one of these Ti(IV)-salan compounds, Ti-salan-dipic [2], which has hydro-lytic stability on the order of weeks. Not only will this allow us to shed some light on the still un...... the physical characteristics are extremely desirable: 45Ti has a 3 hour half-life, a positron branching ratio of 85 %, a low Eβmax of 1.04 MeV, and negligible secondary gamma emission. In terms of isotope production, 45Ti is transmuted from naturally mono-isotopic 45Sc by low energy proton irradiation...... to a water-cooled silver plate. The activated foil was dissolved in 4M HCl, dried under argon at 120 oC, and taken back up in 12M HCl. Here, four (i-iv below) different approaches to removing the Ti from the Sc and labeling were taken with varying success. Briefly: i. 45Ti was separated on hydroxamate resin...

A fluorescence-based hydrolytic enzyme activity assay for quantifying toxic effects of Roundup® to Daphnia magna

DEFF Research Database (Denmark)

Ørsted, Michael; Roslev, Peter

2015-01-01

Daphnia magna is a widely used model organism for aquatic toxicity testing. In the present study, we investigated the hydrolytic enzyme activity of D. magna after exposure to toxicant stress. In vivo enzyme activity was quantified using 15 fluorogenic enzyme probes based on 4-methylumbelliferyl...... or 7-amino-4-methylcoumarin. Probing D. magna enzyme activity was evaluated using short-term exposure (24-48 h) to the reference chemical K2Cr2O7, or the herbicide formulation Roundup®. Toxicant induced changes in hydrolytic enzyme activity were compared to changes in mobility (ISO 6341). The results...... showed that hydrolytic enzyme activity was quantifiable as a combination of whole body fluorescence of D. magna, and fluorescence of the surrounding water. Exposure of D. magna to lethal and sublethal concentrations of Roundup® resulted in loss of whole body enzyme activity, and release of cell...

Poly[(ethylene oxide)-co-(methylene ethylene oxide)]: A hydrolytically-degradable poly(ethylene oxide) platform.

Science.gov (United States)

Lundberg, Pontus; Lee, Bongjae F; van den Berg, Sebastiaan A; Pressly, Eric D; Lee, Annabelle; Hawker, Craig J; Lynd, Nathaniel A

2012-11-20

A facile method for imparting hydrolytic degradability to poly(ethylene oxide) (PEO), compatible with current PEGylation strategies, is presented. By incorporating methylene ethylene oxide (MEO) units into the parent PEO backbone, complete degradation was defined by the molar incorporation of MEO, and the structure of the degradation byproducts was consistent with an acid-catalyzed vinyl-ether hydrolysis mechanism. The hydrolytic degradation of poly[(ethylene oxide)-co-(methylene ethylene oxide)] was pH-sensitive, with degradation at pH 5 being significantly faster than at pH 7.4 at 37 °C in PBS buffer while long-term stability could be obtained in either the solid-state or at pH 7.4 at 6 °C.

Melting Heat in Radiative Flow of Carbon Nanotubes with Homogeneous-Heterogeneous Reactions

Science.gov (United States)

Hayat, Tasawar; Muhammad, Khursheed; Muhammad, Taseer; Alsaedi, Ahmed

2018-04-01

The present article provides mathematical modeling for melting heat and thermal radiation in stagnation-point flow of carbon nanotubes towards a nonlinear stretchable surface of variable thickness. The process of homogeneous-heterogeneous reactions is considered. Diffusion coefficients are considered equal for both reactant and autocatalyst. Water and gasoline oil are taken as base fluids. The conversion of partial differential system to ordinary differential system is done by suitable transformations. Optimal homotopy technique is employed for the solutions development of velocity, temperature, concentration, skin friction and local Nusselt number. Graphical results for various values of pertinent parameters are displayed and discussed. Our results indicate that the skin friction coefficient and local Nusselt number are enhanced for larger values of nanoparticles volume fraction.

Hydrolytic stability of polycarbonate-based polyurethane elastomers tested in physiologically simulated conditions

Czech Academy of Sciences Publication Activity Database

Serkis, Magdalena; Špírková, Milena; Poreba, Rafal; Hodan, Jiří; Kredatusová, Jana; Kubies, Dana

2015-01-01

Roč. 119, September (2015), s. 23-34 ISSN 0141-3910 R&D Projects: GA ČR(CZ) GA13-06700S Institutional support: RVO:61389013 Keywords : polyurethane * elastomer * hydrolytic stability Subject RIV: CD - Macromolecular Chemistry Impact factor: 3.120, year: 2015

Innovative Sol-Gel Routes for the Bottom-up Preparation of Heterogeneous Catalysts.

Science.gov (United States)

Debecker, Damien P

2017-12-11

Heterogeneous catalysts can be prepared by different methods offering various levels of control on the final properties of the solid. In this account, we exemplify bottom-up preparation routes that are based on the sol-gel chemistry and allow to tailor some decisive properties of solid catalysts. First, an emulsion templating strategy is shown to lead to macrocellular self-standing monoliths with a macroscopic 3D structure. The latter can be used as catalyst or catalyst supports in flow chemistry, without requiring any subsequent shaping step. Second, the aerosol-assisted sol-gel process allows for the one-step and continuous production of porous mixed oxides. Tailored textural properties can be obtained together with an excellent control on composition and homogeneity. Third, the application of non-hydrolytic sol-gel routes, in the absence of water, leads to mixed oxides with outstanding textural properties and with peculiar surface chemistry. In all cases, the resulting catalytic performance can be correlated with the specificities of the preparation routes presented. This is exemplified in catalytic reactions in the fields of biomass conversion, petro chemistry, enantioselective organic synthesis, and air pollution mitigation. © 2017 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Towards early detection of the hydrolytic degradation of poly(bisphenol A)carbonate by hyphenated liquid chromatography and comprehensive two-dimensional liquid chromatography

NARCIS (Netherlands)

Coulier, L.; Kaal, E.R.; Hankemeier, Th.

2006-01-01

The hydrolytic degradation of poly(bisphenol A)carbonate (PC) has been characterized by various liquid chromatography techniques. Size exclusion chromatography (SEC) showed a significant decrease in molecular mass as a result of hydrolytic degradation, while 'liquid chromatography at critical

High performance dental resin composites with hydrolytically stable monomers.

Science.gov (United States)

Wang, Xiaohong; Huyang, George; Palagummi, Sri Vikram; Liu, Xiaohui; Skrtic, Drago; Beauchamp, Carlos; Bowen, Rafael; Sun, Jirun

2018-02-01

The objectives of this project were to: 1) develop strong and durable dental resin composites by employing new monomers that are hydrolytically stable, and 2) demonstrate that resin composites based on these monomers perform superiorly to the traditional bisphenol A glycidyl dimethacrylate/triethylene glycol dimethacrylate (Bis-GMA/TEGDMA) composites under testing conditions relevant to clinical applications. New resins comprising hydrolytically stable, ether-based monomer, i.e., triethylene glycol divinylbenzyl ether (TEG-DVBE), and urethane dimethacrylate (UDMA) were produced via composition-controlled photo-polymerization. Their composites contained 67.5wt% of micro and 7.5wt% of nano-sized filler. The performances of both copolymers and composites were evaluated by a battery of clinically-relevant assessments: degree of vinyl conversion (DC: FTIR and NIR spectroscopy); refractive index (n: optical microscopy); elastic modulus (E), flexural strength (F) and fracture toughness (K IC ) (universal mechanical testing); Knoop hardness (HK; indentation); water sorption (W sp ) and solubility (W su ) (gravimetry); polymerization shrinkage (S v ; mercury dilatometry) and polymerization stress (tensometer). The experimental UDMA/TEG-DVBE composites were compared with the Bis-GMA/TEGDMA composites containing the identical filler contents, and with the commercial micro hybrid flowable composite. UDMA/TEG-DBVE composites exhibited n, E, W sp , W su and S v equivalent to the controls. They outperformed the controls with respect to F (up to 26.8% increase), K IC (up to 27.7% increase), modulus recovery upon water sorption (full recovery vs. 91.9% recovery), and stress formation (up to 52.7% reduction). In addition, new composites showed up to 27.7% increase in attainable DC compared to the traditional composites. Bis-GMA/TEGDMA controls exceeded the experimental composites with respect to only one property, the composite hardness. Significantly, up to 18.1% lower HK values in

Numerical tackling for viscoelastic fluid flow in rotating frame considering homogeneous-heterogeneous reactions

Science.gov (United States)

Maqsood, Najwa; Mustafa, M.; Khan, Junaid Ahmad

This study provides a numerical treatment for rotating flow of viscoelastic (Maxwell) fluid bounded by a linearly deforming elastic surface. Mass transfer analysis is carried out in the existence of homogeneous-heterogeneous reactions. By means of usual transformation, the governing equations are changed into global similarity equations which have been tackled by an expedient shooting approach. A contemporary numerical routine bvp4c of software MATLAB is also opted to develop numerical approximations. Both methods of solution are found in complete agreement in all the cases. Velocity and concentration profiles are computed and elucidated for certain range of viscoelastic fluid parameter. The solutions contain a rotation-strength parameter λ that has a considerable impact on the flow fields. For sufficiently large value of λ , the velocity fields are oscillatory decaying function of the non-dimensional vertical distance. Concentration distribution at the surface is found to decrease upon increasing the strengths of chemical reactions. A comparison of present computations is made with those of already published ones and such comparison appears convincing.

Cesium Carbonate as a Heterogeneous Base Catalyst for Synthesis of 2-Aminothiophenes via Gewald Reaction

Energy Technology Data Exchange (ETDEWEB)

Moeinpour, Farid [Islamic Azad University, Bandar Abbas Branch, Abbas (Iran, Islamic Republic of); Omidinia, Raheleh; Dorostkar-Ahmadi, Nadieh; Khoshdeli, Bentalhoda [Islamic Azad University, Mashhad Branch, Mashhad (Iran, Islamic Republic of)

2011-06-15

We have reported a new simple catalytic method for the synthesis of 2-aminothiophenes via Gewald reaction using Cs{sub 2}CO{sub 3} as an efficient, reusable and green heterogeneous catalyst under heating conditions in refluxing ethanol. The catalyst could be recycled after a simple workup and reused at least three runs without appreciable reduction in its catalytic activity. Low catalyst loading, clean reaction profiles, simple experimental and workup procedures and high yields are some advantages of this protocol. The synthesis of substituted 2-aminothiophenes is attractive to chemical researchers as they are important intermediates in organic synthesis and frequently used as the scaffold motif of a variety of agrochemicals, dyes, and biologically active products. Thus, because of their wide utility, researchers have synthesized the substituted 2-aminothiophenes via efficient and convenient methods. The one-pot cyclocondensation of ketones with an activated α-hydrogen, a cyanomethylene containing an electron-withdrawing group such as cyanoacetate and elemental sulfur in the presence of organic base, for example, morpholine, diethylamine, etc, known as the Gewald reaction, has been one of the most well-studied multicomponent reactions in recent years. To extend the scope of the reaction, many alterations have been made to the original Gewald's base-catalyzed, two-component combination of α-mercapto ketones with cyanoacetate by varying the components and the conditions.

Quantitative iTRAQ secretome analysis of aspergillus niger reveals novel hydrolytic enzymes

NARCIS (Netherlands)

Adav, S.S.; Li, A.A.; Manavalan, A.; Punt, P.; Sze, S.K.

2010-01-01

The natural lifestyle of Aspergillus niger made them more effective secretors of hydrolytic proteins and becomes critical when this species were exploited as hosts for the commercial secretion of heterologous proteins. The protein secretion profile of A. niger and its mutant at different pH was

Influence of pH on Morphology and Structure during Hydrolytic Degradation of the Segmented GL-b-[GL-co-TMC-co-CL]-b-GL Copolymer

Directory of Open Access Journals (Sweden)

Yolanda Márquez

2015-09-01

Full Text Available Hydrolytic degradation in media having a continuous variation of pH from 2 to 12 was studied for a copolymer having two polyglycolide hard blocks and a middle soft segment constituted by glycolide, trimethylene carbonate, and ɛ-caprolactone units. The last units were susceptible to cross-linking reactions by γ irradiation that led to an increase of the molecular weight of the sample. Nevertheless, the susceptibility to hydrolytic degradation was enhanced with respect to non-irradiated samples and consequently such samples were selected to analyze the degradation process through weight loss measurements and the evaluation of changes on molecular weight, morphology, and SAXS patterns. Results reflected the different hydrolytic mechanisms that took place in acid and basic media and the different solubilization of the degradation products. Thus, degradation was faster and solubilization higher in the basic media. In this case, fibers showed a high surface erosion and the formation of both longitudinal and deep circumferential cracks that contrasted with the peeling process detected at intermediate pHs (from 6 to 8 and the absence of longitudinal cracks at low pHs. SAXS measurements indicated that degradation was initiated through the hydrolysis of the irregular molecular folds placed on the amorphous interlamellar domains but also affected lamellar crystals at the last stages. Subsequent heating processes performed with degraded samples were fundamental to reveal the changes in microstructure that occurred during degradation and even the initial lamellar arrangement. In particular, the presence of interfibrillar domains and the disposition of lamellar domains at different levels along the fiber axis for a determined cross-section were evidenced.

Influence of preparation conditions of hollow silica–nickel composite spheres on their catalytic activity for hydrolytic dehydrogenation of ammonia borane

Energy Technology Data Exchange (ETDEWEB)

Umegaki, Tetsuo, E-mail: umegaki.tetsuo@nihon-u.ac.jp [Department of Materials and Applied Chemistry, College of Science and Engineering, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8308 (Japan); Seki, Ayano [Department of Materials and Applied Chemistry, College of Science and Engineering, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8308 (Japan); Xu, Qiang [National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577 (Japan); Kojima, Yoshiyuki [Department of Materials and Applied Chemistry, College of Science and Engineering, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8308 (Japan)

2014-03-05

Highlights: • We study influence of preparation conditions on activity of hollow silica–nickel composite spheres. • The activity for hydrolytic dehydrogenation of NH{sub 3}BH{sub 3} increases with increase of Si+Ni content. • The particle size distribution affects the activity and reducibility of active nickel species. • The amount of PS residue in the hollow spheres decreases by treatment of as-prepared sample in toluene. -- Abstract: In this paper, we investigated influence of preparation conditions of hollow silica–nickel composite spheres on their morphology and catalytic activity for hydrolytic dehydrogenation of ammonia borane. In the preparation method of this study, when silica–nickel composite shells were coated on polystyrene templates by the sol–gel method using L(+)-arginine as the promoter for the reaction to form silica–nickel composite shell, the polystyrene templates were dissolved subsequently, even synchronously, in the same medium to form hollow spheres. The as-prepared silica–nickel composite spheres were characterized by transmission electron microscopy and scanning electron microscopy. The effects of Si+Ni content on the morphology were systematically evaluated. All the as-prepared hollow silica–nickel composite spheres have the similar morphology as identified by SEM and TEM measurement. Homogeneity of the hollow silica–nickel composite spheres increases with the increase in the Si+Ni content as shown by the laser diffraction particle size analysis. The catalytic activities of the hollow silica–nickel composite spheres for hydrolytic dehydrogenation of ammonia borane prepared with different Si+Ni contents were compared. The catalytic activity for the hydrogen evolution in the presence of the hollow spheres increases with the increase of Si+Ni content. The results of FTIR spectra of the hollow silica–nickel composite spheres indicate that a certain amount of residual PS templates exists in hollow silica�

Numerical analysis of MHD Carreau fluid flow over a stretching cylinder with homogenous-heterogeneous reactions

Science.gov (United States)

Khan, Imad; Ullah, Shafquat; Malik, M. Y.; Hussain, Arif

2018-06-01

The current analysis concentrates on the numerical solution of MHD Carreau fluid flow over a stretching cylinder under the influences of homogeneous-heterogeneous reactions. Modelled non-linear partial differential equations are converted into ordinary differential equations by using suitable transformations. The resulting system of equations is solved with the aid of shooting algorithm supported by fifth order Runge-Kutta integration scheme. The impact of non-dimensional governing parameters on the velocity, temperature, skin friction coefficient and local Nusselt number are comprehensively delineated with the help of graphs and tables.

Numerical study for melting heat transfer and homogeneous-heterogeneous reactions in flow involving carbon nanotubes

Science.gov (United States)

Hayat, Tasawar; Muhammad, Khursheed; Alsaedi, Ahmed; Asghar, Saleem

2018-03-01

Present work concentrates on melting heat transfer in three-dimensional flow of nanofluid over an impermeable stretchable surface. Analysis is made in presence of porous medium and homogeneous-heterogeneous reactions. Single and multi-wall CNTs (carbon nanotubes) are considered. Water is chosen as basefluid. Adequate transformations yield the non-linear ordinary differential systems. Solution of emerging problems is obtained using shooting method. Impacts of influential variables on velocity and temperature are discussed graphically. Skin friction coefficient and Nusselt number are numerically discussed. The results for MWCNTs and SWCNTs are compared and examined.

The effect of the source of microorganisms on adaptation of hydrolytic consortia dedicated to anaerobic digestion of maize silage.

Science.gov (United States)

Poszytek, Krzysztof; Pyzik, Adam; Sobczak, Adam; Lipinski, Leszek; Sklodowska, Aleksandra; Drewniak, Lukasz

2017-08-01

The main aim of this study was to evaluate the effect of the source of microorganisms on the selection of hydrolytic consortia dedicated to anaerobic digestion of maize silage. The selection process was investigated based on the analysis of changes in the hydrolytic activity and the diversity of microbial communities derived from (i) a hydrolyzer of a commercial agricultural biogas plant, (ii) cattle slurry and (iii) raw sewage sludge, during a series of 10 passages. Following the selection process, the adapted consortia were thoroughly analyzed for their ability to utilize maize silage and augmentation of anaerobic digestion communities. The results of selection of the consortia showed that every subsequent passage of each consortium leads to their adaptation to degradation of maize silage, which was manifested by the increased hydrolytic activity of the adapted consortia. Biodiversity analysis (based on the 16S rDNA amplicon sequencing) confirmed the changes microbial community of each consortium, and showed that after the last (10th) passage all microbial communities were dominated by the representatives of Lactobacillaceae, Prevotellaceae, Veillonellaceae. The results of the functional analyses showed that the adapted consortia improved the efficiency of maize silage degradation, as indicated by the increase in the concentration of glucose and volatile fatty acids (VFAs), as well as the soluble chemical oxygen demand (sCOD). Moreover, bioaugmentation of anaerobic digestion communities by the adapted hydrolytic consortia increased biogas yield by 10-29%, depending on the origin of the community. The obtained results also indicate that substrate input (not community origin) was the driving force responsible for the changes in the community structure of hydrolytic consortia dedicated to anaerobic digestion. Copyright © 2017 Elsevier Ltd. All rights reserved.

Gibbs Free Energy of Hydrolytic Water Molecule in Acyl-Enzyme Intermediates of a Serine Protease: A Potential Application for Computer-Aided Discovery of Mechanism-Based Reversible Covalent Inhibitors.

Science.gov (United States)

Masuda, Yosuke; Yamaotsu, Noriyuki; Hirono, Shuichi

2017-01-01

In order to predict the potencies of mechanism-based reversible covalent inhibitors, the relationships between calculated Gibbs free energy of hydrolytic water molecule in acyl-trypsin intermediates and experimentally measured catalytic rate constants (k cat ) were investigated. After obtaining representative solution structures by molecular dynamics (MD) simulations, hydration thermodynamics analyses using WaterMap™ were conducted. Consequently, we found for the first time that when Gibbs free energy of the hydrolytic water molecule was lower, logarithms of k cat were also lower. The hydrolytic water molecule with favorable Gibbs free energy may hydrolyze acylated serine slowly. Gibbs free energy of hydrolytic water molecule might be a useful descriptor for computer-aided discovery of mechanism-based reversible covalent inhibitors of hydrolytic enzymes.

Formation of nitro-PAHs from the heterogeneous reaction of ambient particle-bound PAHs with NO3/N2O5

Science.gov (United States)

Zimmermann, K.; Jariyasopit, N.; Simonich, S. L.; Atkinson, R.; Arey, J.

2012-12-01

Polycyclic aromatic hydrocarbons (PAHs) and their nitrated derivatives (nitro-PAHs) have been shown to be mutagenic in bacterial and mammalian assays and are classified as probable human carcinogens. Semi-volatile PAHs partition between the gas and particulate phases, depending on their liquid-phase vapor pressures and ambient temperatures. These PAHs have been extensively measured in ambient particulate matter and can ultimately undergo long-range transport from source regions (e.g., China to the western USA) (1). During transport these particle-bound PAHs may undergo reaction with NO3/N2O5 to form nitro-PAH derivatives. Previous studies of heterogeneous nitration of PAHs have used particles composed of graphite, diesel soot, and wood smoke (2-4). This study investigates the heterogeneous formation of nitro-PAHs from ambient particle-bound PAHs from Beijing, China and sites located within the Los Angeles air basin. These ambient particle samples, along with filters coated with isotopically labeled PAHs, were exposed to a mix of NO2/NO3/N2O5 in a 7000 L Teflon chamber, with analysis focused on the heterogeneous formation of molecular weight 247 and 273 nitro-PAHs. The heterogeneous formation of certain nitro-PAHs (including1-nitropyrene and 1- and 2-nitrotriphenylene) was observed for some, but not all, ambient samples. Formation of nitro-PAHs typically formed through gas-phase reactions (2-nitrofluoranthene and 2-nitropyrene) was not observed. The effect of particle age and local photochemical conditions during sampling on the degree of nitration in environmental chamber reactions, as well as ambient implications, will be presented. 1. Primbs, T.; Simonich, S.; Schmedding, D.; Wilson, G.; Jaffe, D.; Takami, A.; Kato, S.; Hatakeyama, S.; Kajii, Y. Environ. Sci. Technol. 2007, 41, 3551-3558. 2. Esteve, W.; Budzinski, H.; Villenave, E. Atmospheric Environment 2004, 38, 6063-6072. 3. Nguyen, M.; Bedjanian, Y.; Guilloteau, A. Journal of Atmospheric Chemistry 2009, 62

Correlation between discrete probability and reaction front propagation rate in heterogeneous mixtures

Science.gov (United States)

Naine, Tarun Bharath; Gundawar, Manoj Kumar

2017-09-01

We demonstrate a very powerful correlation between the discrete probability of distances of neighboring cells and thermal wave propagation rate, for a system of cells spread on a one-dimensional chain. A gamma distribution is employed to model the distances of neighboring cells. In the absence of an analytical solution and the differences in ignition times of adjacent reaction cells following non-Markovian statistics, invariably the solution for thermal wave propagation rate for a one-dimensional system with randomly distributed cells is obtained by numerical simulations. However, such simulations which are based on Monte-Carlo methods require several iterations of calculations for different realizations of distribution of adjacent cells. For several one-dimensional systems, differing in the value of shaping parameter of the gamma distribution, we show that the average reaction front propagation rates obtained by a discrete probability between two limits, shows excellent agreement with those obtained numerically. With the upper limit at 1.3, the lower limit depends on the non-dimensional ignition temperature. Additionally, this approach also facilitates the prediction of burning limits of heterogeneous thermal mixtures. The proposed method completely eliminates the need for laborious, time intensive numerical calculations where the thermal wave propagation rates can now be calculated based only on macroscopic entity of discrete probability.

Hydrolytic bacteria in mesophilic and thermophilic degradation of plant biomass

Energy Technology Data Exchange (ETDEWEB)

Zverlov, Vladimir V.; Hiegl, Wolfgang; Koeck, Daniela E.; Koellmeier, Tanja; Schwarz, Wolfgang H. [Department of Microbiology, Technische Universitaet Muenchen, Freising-Weihenstephan (Germany); Kellermann, Josef [Max Planck Institute for Biochemistry, Am Klopferspitz, Martinsried (Germany)

2010-12-15

Adding plant biomass to a biogas reactor, hydrolysis is the first reaction step in the chain of biological events towards methane production. Maize silage was used to enrich efficient hydrolytic bacterial consortia from natural environments under conditions imitating those in a biogas plant. At 55-60 C a more efficient hydrolyzing culture could be isolated than at 37 C. The composition of the optimal thermophilic bacterial consortium was revealed by sequencing clones from a 16S rRNA gene library. A modified PCR-RFLP pre-screening method was used to group the clones. Pure anaerobic cultures were isolated. 70% of the isolates were related to Clostridium thermocellum. A new culture-independent method for identification of cellulolytic enzymes was developed using the isolation of cellulose-binding proteins. MALDI-TOF/TOF analysis and end-sequencing of peptides from prominent protein bands revealed cellulases from the cellulosome of C. thermocellum and from a major cellulase of Clostridium stercorarium. A combined culture of C. thermocellum and C. stercorarium was shown to excellently degrade maize silage. A spore preparation method suitable for inoculation of maize silage and optimal hydrolysis was developed for the thermophilic bacterial consortium. This method allows for concentration and long-term storage of the mixed culture for instance for inoculation of biogas fermenters. (Copyright copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Dynamic Ureas with Fast and pH-Independent Hydrolytic Kinetics.

Science.gov (United States)

Cai, Kaimin; Ying, Hanze; Cheng, Jianjun

2018-04-06

Low cost, high performance hydrolysable polymers are of great importance in biomedical applications and materials industries. While many applications require materials to have a degradation profile insensitive to external pH to achieve consistent release profiles under varying conditions, hydrolysable chemistry techniques developed so far have pH-dependent hydrolytic kinetics. This work reports the design and synthesis of a new type of hydrolysable polymer that has identical hydrolysis kinetics from pH 3 to 11. The unprecedented pH independent hydrolytic kinetics of the aryl ureas were shown to be related to the dynamic bond dissociation controlled hydrolysis mechanism; the resulting hindered poly(aryl urea) can be degraded with a hydrolysis half-life of 10 min in solution. More importantly, these fast degradable hindered aromatic polyureas can be easily prepared by addition polymerization from commercially available monomers and are resistant to hydrolysis in solid form for months under ambient storage conditions. The combined features of good stability in solid state and fast hydrolysis at various pH values is unprecedented in polyurea material, and will have implications for materials design and applications, such as sacrificial coatings and biomaterials. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hydrolytic study of the copolymer Poly pyrrole/ Polyethyleneglycol and Poly pyrrole synthesized by plasma

International Nuclear Information System (INIS)

Colin, E.; Enriquez, M.A.; Olayo, M.G.; Cruz, G.J.; Carapia, L.; Romero, M.; Morales, J.; Olayo, R.

2006-01-01

In this work the study about the hydrolytic compatibility of semiconductor polymers, copolymer Poly pyrrole/ Polyethyleneglycol (PPy/PEG) and Poly pyrrole (PPy) for their possible use as biomaterials. The polymers were synthesized by plasma between 10 and 100 W, with discharges of splendor RF to 13.5 MHz with resistive coupling. The hydrolytic affinity was evaluated calculating the contact angle with solutions of NaCl, NaCl-MgSO 4 and Krebs-Ringer. The results show a hydrophilicity increment due to the increase of the surface ruggedness with the synthesis energy. On the contrary, the crystallinity diminishes when increasing the power in PPy and it stays approximately constant in PPy/PEG. The electric conductivity presents a growth from 2 to 4 magnitude orders in function of the water content in the polymers. (Author)

Cellulose Triacetate Synthesis from Cellulosic Wastes by Heterogeneous Reactions

Directory of Open Access Journals (Sweden)

Sherif Shawki Z. Hindi

2015-06-01

Full Text Available Cellulosic fibers from cotton fibers (CF, recycled writing papers (RWP, recycled newspapers (RN, and macerated woody fibers of Leucaena leucocephala (MWFL were acetylated by heterogeneous reactions with glacial acetic acid, concentrated H2SO4, and acetic anhydride. The resultant cellulose triacetate (CTA was characterized for yield and solubility as well as by using 1H-NMR spectroscopy and SEM. The acetylated product (AP yields for CF, RWP, RN, and MWFL were 112, 94, 84, and 73%, respectively. After isolation of pure CTA from the AP, the CTA yields were 87, 80, 68, and 54%. The solubility test for the CTA’s showed a clear solubility in chloroform, as well as mixture of chloroform and methanol (9:1v/v and vice versa for acetone. The degree of substitution (DS values for the CTA’s produced were nearly identical and confirmed the presence of CTA. In addition, the pore diameter of the CTA skeleton ranged from 0.072 to 0.239 µm for RWP and RN, and within the dimension scale of the CTA pinholes confirm the synthesis of CTA. Accordingly, pouring of the AP liquor at 25 °C in distilled water at the end of the acetylation and filtration did not hydrolyze the CTA to cellulose diacetate.

Unequal diffusivities case of homogeneous–heterogeneous reactions within viscoelastic fluid flow in the presence of induced magnetic-field and nonlinear thermal radiation

Directory of Open Access Journals (Sweden)

I.L. Animasaun

2016-06-01

Full Text Available This article presents the effects of nonlinear thermal radiation and induced magnetic field on viscoelastic fluid flow toward a stagnation point. It is assumed that there exists a kind of chemical reaction between chemical species A and B. The diffusion coefficients of the two chemical species in the viscoelastic fluid flow are unequal. Since chemical species B is a catalyst at the horizontal surface, hence homogeneous and heterogeneous schemes are of the isothermal cubic autocatalytic reaction and first order reaction respectively. The transformed governing equations are solved numerically using Runge–Kutta integration scheme along with Newton’s method. Good agreement is obtained between present and published numerical results for a limiting case. The influence of some pertinent parameters on skin friction coefficient, local heat transfer rate, together with velocity, induced magnetic field, temperature, and concentration profiles is illustrated graphically and discussed. Based on all of these assumptions, results indicate that the effects of induced magnetic and viscoelastic parameters on velocity, transverse velocity and velocity of induced magnetic field are almost the same but opposite in nature. The strength of heterogeneous reaction parameter is very helpful to reduce the concentration of bulk fluid and increase the concentration of catalyst at the surface.

Heterogeneous ozonation reactions of PAHs and fatty acid methyl esters in biodiesel particulate matter

Science.gov (United States)

Kasumba, John; Holmén, Britt A.

2018-02-01

Numerous studies have examined the oxidation of PAHs found in diesel particulate matter (PM) by ozone, but no studies have investigated the ozone oxidation of biodiesel exhaust PM. Fatty acid methyl esters (FAMEs), found in high abundance in biodiesel PM, can potentially alter the kinetics of the reactions between atmospheric oxidants such as ozone and particle-phase PAHs. In this study, the heterogeneous reactivity of 16 EPA PAHs upon 24 h exposure to 0.4 ppm ozone in the presence (PAH + FAMES) and absence (PAH-only) of FAMEs was investigated at room temperature and 50% relative humidity. The ozone-reactivity of the PAHs detected in 20% biodiesel (B20) exhaust PM was also investigated. In the absence of FAMEs, the pseudo-first order ozone reaction rate constant, kO 3 , of PAHs varied from 0.086 ± 0.030 hr-1 (chrysene) to 0.184 ± 0.078 hr-1 (anthracene). In the presence of FAMEs, kO 3 of the PAHs varied between 0.013 ± 0.012 hr-1 (benzo[b]fluoranthene) and 0.168 ± 0.028 hr-1 (benzo[a]pyrene), and with the exception of benzo[a]pyrene, the kO 3 of PAHs were 1.2-8 times lower compared to those obtained during the PAH-only ozone exposure. Only one PAH, benzo[a]pyrene (BaP), did not show a significant change in kO3 with addition of FAMEs. Phenanthrene, fluoranthene, and pyrene, the only PAHs detected in the B20 PM, had kO 3 values about 4 times lower in B20 PM than those obtained when spiked PAHs-only were exposed to ozone. The kO 3 values of phenanthrene and fluoranthene in the B20 PM were 2 times higher than rates obtained when the PAH mix was exposed to ozone in the presence of the FAMEs. In contrast, pyrene's kO 3 in the B20 PM was about 2 times lower than that obtained for the PAH + FAMEs exposure. Observed differences in PAH behavior demonstrate individual PAH heterogeneous reactivity with gas-phase ozone is sensitive to PAH (vapor pressure, solubility/sorption to matrix components, chemical reactivity) as well as substrate properties (PAH and O3 diffusivity

Heterogeneous Reaction of SO2 on Manganese Oxides: the Effect of Crystal Structure and Relative Humidity.

Science.gov (United States)

Yang, Weiwei; Zhang, Jianghao; Ma, Qingxin; Zhao, Yan; Liu, Yongchun; He, Hong

2017-07-03

Manganese oxides from anthropogenic sources can promote the formation of sulfate through catalytic oxidation of SO 2 . In this study, the kinetics of SO 2 reactions on MnO 2 with different morphologies (α, β, γ and δ) was investigated using flow tube reactor and in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). Under dry conditions, the reactivity towards SO 2 uptake was highest on δ-MnO 2 but lowest on β-MnO 2 , with a geometric uptake coefficient (γ obs ) of (2.42 ± 0.13) ×10 -2 and a corrected uptake coefficient (γ c ) of (1.48 ± 0.21) ×10 -6 for the former while γ obs of (3.35 ± 0.43) ×10 -3 and γ c of (7.46 ± 2.97) ×10 -7 for the latter. Under wet conditions, the presence of water altered the chemical form of sulfate and was in favor for the heterogeneous oxidation of SO 2 . The maximum sulfate formation rate was reached at 25% RH and 45% for δ-MnO 2 and γ-MnO 2 , respectively, possibly due to their different crystal structures. The results suggest that morphologies and RH are important factors influencing the heterogeneous reaction of SO 2 on mineral aerosols, and that aqueous oxidation process involving transition metals of Mn might be a potential important pathway for SO 2 oxidation in the atmosphere.

Saccharification and hydrolytic enzyme production of alkali pre-treated wheat bran by Trichoderma virens under solid state fermentation.

Science.gov (United States)

El-Shishtawy, Reda M; Mohamed, Saleh A; Asiri, Abdullah M; Gomaa, Abu-Bakr M; Ibrahim, Ibrahim H; Al-Talhi, Hasan A

2015-05-28

In continuation of our previously interest in the saccharification of agriculture wastes by Bacillus megatherium in solid state fermentation (SSF), we wish to report an investigation and comparative evaluation among Trichoderma sp. for the saccharification of four alkali-pretreated agricultural residues and production of hydrolytic enzymes, carboxymethyl cellulase (CMCase), filter paperase (FPase), pectinase (PGase) and xylanase (Xylase) in SSF. The optimization of the physiological conditions of production of hydrolytic enzymes and saccharification content from Trichoderma virens using alkali-pretreated wheat bran was the last goal. The physico-chemical parameters of SSF include incubation time, incubation temperature, moisture content of the substrate, incubation pH, supplementation with carbon and nitrogen sources were optimized. Saccharification of different solid state fermentation sources wheat bran, date's seeds, grass and palm leaves, were tested for the production of fermentable sugar by Trichoderma sp. The maximum production of hydrolytic enzymes CMCase, FPase, PGase and Xylase and saccharification content were obtained on wheat bran. Time course, moisture content, optimum temperature, optimum pH, supplementation with carbon and nitrogen sources were optimized to achieve the maximum production of the hydrolytic enzymes, protein and total carbohydrate of T. virens using alkali pre-treated wheat bran. The maximum production of CMCase, FPase, PGase, Xylase, protein and carbohydrate content was recorded at 72 h of incubation, 50-70 % moisture, temperature 25-35 °C and pH 5. The influence of supplementary carbon and nitrogen sources was studied. While lactose and sucrose enhanced the activity of PGase from 79.2 to 582.9 and 632.6 U/g, starch inhibited all other enzymes. This was confirmed by maximum saccharification content. Among the nitrogen sources, yeast extract and urea enhanced the saccharification content and CMCase, PGase and Xylase. The results of

Rapid heating evaporation of Pb(NO3)2. Evidence for heterogeneous ion-molecule reactions

International Nuclear Information System (INIS)

Radus, T.P.; Udseth, H.R.; Friedman, L.

1979-01-01

A mass spectrometric investigation of the lead nitrate system is reported in which the lead nitrate was evaporated from a probe filament that was heated as rapidly as 5000 0 C/s. Both electron impact (EI) and chemical ionization (CI) source techniques were used in this study. Fragment ions and decomposition products were observed under EI conditions. Under CI conditions solvated fragment ions and protonated solvated molecular ions were detected. Temperature measurements of rates of evaporation were made by monitoring the resistance of the probe filament as it was heated. Activation energies calculated by using these temperature coefficients of evaporation rates indicate that evaporations under CI conditions are assisted by heterogeneous ion-molecule reactions

Investigation of the hydrolytic and radiolytic degradation of HEH[EHP

International Nuclear Information System (INIS)

Peterman, Dean Richard; McDowell, Rocklan George; Zarzana, Christopher Andrew; Johnson, Kristyn Marie; Rowe, Salene Marie; Groenewold, Gary Steven

2016-01-01

The extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) is a component used in both the Advanced TALSPEAK and ALSEP solvent extraction processes. The most likely compound formed via hydrolytic or radiolytic degradation of HEH[EHP] would be the phosphonic acid 2-ethylhexylphosphonic acid (H2EHP) that is formed by cleavage of the P-O-R bond. Thus far, attempts to detect H2EHP by gas chromatography or mass spectrometry have not been successful. The inability to detect this proposed degradation product in analytical samples is likely due to inadequate analysis techniques, lack of H2EHP production, further decomposition of H2EHP forming products not detectable by the employed analytical techniques, or a combination of all of the above scenarios. In order to address this problem, commercially available alkylphosphonic acids were acquired and used as surrogates for H2EHP in the gas chromatography and mass spectrometry analysis of samples. Once the ability to detect alkylphosphonic acid compounds was confirmed, these analytical techniques were used to confirm the production of H2EHP in samples of HEH[EHP] exposed to nitric acid and nitric acid plus gamma radiation. This report provides a brief summary of results and serves as documentation of the completion the level four milestone M4FT-16IN030102025 “Investigate the hydrolytic and radiolytic degradation of HEH[EHP]”.

Characterisation and properties of homo- and heterogenously phosphorylated nanocellulose.

Science.gov (United States)

Kokol, Vanja; Božič, Mojca; Vogrinčič, Robert; Mathew, Aji P

2015-07-10

Nano-sized cellulose ester derivatives having phosphoryl side groups were synthesised by phosphorylation of nanofibrilated cellulose (NFC) and nanocrystaline cellulose (NCC), using different heterogeneous (in water) and homogeneous (in molten urea) processes with phosphoric acid as phosphoryl donor. The phosphorylation mechanism, efficacy, stability, as well as its influence on the NC crystallinity and thermal properties, were evaluated using ATR-FTIR and (13)C NMR spectroscopies, potentiometric titration, capillary electrophoresis, X-ray diffraction, colorimetry, thermogravimmetry and SEM. Phosphorylation under both processes created dibasic phosphate and monobasic tautomeric phosphite groups at C6 and C3 positioned hydroxyls of cellulose, yielded 60-fold (∼1,173 mmol/kg) and 2-fold (∼1.038 mmol/kg) higher surface charge density for p-NFC and p-NCC, respectively, under homogenous conditions. None of the phosphorylations affected neither the NC crystallinity degree nor the structure, and noticeably preventing the derivatives from weight loss during the pyrolysis process. The p-NC showed high hydrolytic stability to water at all pH mediums. Reusing of the treatment bath was examined after the heterogeneous process. Copyright © 2015 Elsevier Ltd. All rights reserved.

Significant impacts of heterogeneous reactions on the chemical composition and mixing state of dust particles: A case study during dust events over northern China

Science.gov (United States)

Wang, Zhe; Pan, Xiaole; Uno, Itsushi; Li, Jie; Wang, Zifa; Chen, Xueshun; Fu, Pingqing; Yang, Ting; Kobayashi, Hiroshi; Shimizu, Atsushi; Sugimoto, Nobuo; Yamamoto, Shigekazu

2017-06-01

The impact of heterogeneous reactions on the chemical components and mixing state of dust particles are investigated by observations and an air quality model over northern China between March 27, 2015 and April 2, 2015. Synergetic observations were conducted using a polarization optical particle counter (POPC), a depolarized two-wavelength Lidar and filter samples in Beijing. During this period, dust plume passed through Beijing on March 28, and flew back on March 29 because of synoptic weather changes. Mineral dust mixed with anthropogenic pollutants was simulated using the Nested Air Quality Prediction Modeling System (NAQPMS) to examine the role of heterogeneous processes on the dust. A comparison of observations shows that the NAQPMS successfully reproduces the time series of the vertical profile, particulate matter concentration, and chemical components of fine mode (diameter ≤ 2.5 μm) and coarse mode (2.5 μm mixed with dust particles. The significant alterations of the chemical composition and mixing state of particles due to heterogeneous reactions are important for the direct and indirect climate effects of dust and anthropogenic aerosols.

Continuous Heterogeneous Photocatalysis in Serial Micro-Batch Reactors.

Science.gov (United States)

Pieber, Bartholomäus; Shalom, Menny; Antonietti, Markus; Seeberger, Peter H; Gilmore, Kerry

2018-01-29

Solid reagents, leaching catalysts, and heterogeneous photocatalysts are commonly employed in batch processes but are ill-suited for continuous-flow chemistry. Heterogeneous catalysts for thermal reactions are typically used in packed-bed reactors, which cannot be penetrated by light and thus are not suitable for photocatalytic reactions involving solids. We demonstrate that serial micro-batch reactors (SMBRs) allow for the continuous utilization of solid materials together with liquids and gases in flow. This technology was utilized to develop selective and efficient fluorination reactions using a modified graphitic carbon nitride heterogeneous catalyst instead of costly homogeneous metal polypyridyl complexes. The merger of this inexpensive, recyclable catalyst and the SMBR approach enables sustainable and scalable photocatalysis. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Heterogeneous kinetics, products, and mechanisms of ferulic acid particles in the reaction with NO3 radicals

Science.gov (United States)

Liu, Changgeng; Zhang, Peng; Wen, Xiaoying; Wu, Bin

2017-03-01

Methoxyphenols, as an important component of wood burning, are produced by lignin pyrolysis and considered to be the potential tracers for wood smoke emissions. In this work, the heterogeneous reaction between ferulic acid particles and NO3 radicals was investigated. Six products including oxalic acid, 4-vinylguaiacol, vanillin, 5-nitrovanillin, 5-nitroferulic acid, and caffeic acid were confirmed by gas chromatography-mass spectrometry (GC-MS). In addition, the reaction mechanisms were proposed and the main pathways were NO3 electrophilic addition to olefin and the meta-position to the hydroxyl group. The uptake coefficient of NO3 radicals on ferulic acid particles was 0.17 ± 0.02 and the effective rate constant under experimental conditions was (1.71 ± 0.08) × 10-12 cm3 molecule-1 s-1. The results indicate that ferulic acid degradation by NO3 can be an important sink at night.

Studies on the heterogeneous electron transport and oxygen reduction reaction at metal (Co, Fe) octabutylsulphonylphthalocyanines supported on multi-walled carbon nanotube modified graphite electrode

CSIR Research Space (South Africa)

Mamuru, SA

2010-09-01

Full Text Available Heterogeneous electron transfer dynamics and oxygen reduction reaction (ORR) activities using octabutylsulphonylphthalocyanine complexes of iron (FeOBSPc) and cobalt (CoOBSPc) supported on multi-walled carbon nanotube (MWCNT) platforms have been...

Replacement of traditional seawater-soluble pigments by starch and hydrolytic enzymes in polishing antifouling coatings

DEFF Research Database (Denmark)

Olsen, Søren Martin; Pedersen, L. T.; Dam-Johansen, Kim

2010-01-01

The use of starch and hydrolytic enzymes as replacement for traditional polishing pigments (e.g., Cu2O and ZnO) in antifouling coatings has been investigated. The enzymes facilitate a slow conversion of water-insoluble starch into water-soluble glucose, and dissolution of glucose causes the devel......The use of starch and hydrolytic enzymes as replacement for traditional polishing pigments (e.g., Cu2O and ZnO) in antifouling coatings has been investigated. The enzymes facilitate a slow conversion of water-insoluble starch into water-soluble glucose, and dissolution of glucose causes...... the development of a leached (porous) layer in the wetted, outermost part of the coating. Subsequent water-binder interaction at the pore walls gives rise to polishing, in a manner similar to that of conventional antifouling coatings. Different starch types have been evaluated and classified as potential coating...

Chimeric cellulase matrix for investigating intramolecular synergism between non-hydrolytic disruptive functions of carbohydrate-binding modules and catalytic hydrolysis.

Science.gov (United States)

Wang, Yuguo; Tang, Rentao; Tao, Jin; Wang, Xiaonan; Zheng, Baisong; Feng, Yan

2012-08-24

The conversion of renewable cellulosic biomass is of considerable interest for the production of biofuels and materials. The bottleneck in the efficient conversion is the compactness and resistance of crystalline cellulose. Carbohydrate-binding modules (CBMs), which disrupt crystalline cellulose via non-hydrolytic mechanisms, are expected to overcome this bottleneck. However, the lack of convenient methods for quantitative analysis of the disruptive functions of CBMs have hindered systematic studies and molecular modifications. Here we established a practical and systematic platform for quantifying and comparing the non-hydrolytic disruptive activities of CBMs via the synergism of CBMs and a catalytic module within designed chimeric cellulase molecules. Bioinformatics and computational biology were also used to provide a deeper understanding. A convenient vector was constructed to serve as a cellulase matrix into which heterologous CBM sequences can be easily inserted. The resulting chimeric cellulases were suitable for studying disruptive functions, and their activities quantitatively reflected the disruptive functions of CBMs on crystalline cellulose. In addition, this cellulase matrix can be used to construct novel chimeric cellulases with high hydrolytic activities toward crystalline cellulose.

Chimeric Cellulase Matrix for Investigating Intramolecular Synergism between Non-hydrolytic Disruptive Functions of Carbohydrate-binding Modules and Catalytic Hydrolysis*

Science.gov (United States)

Wang, Yuguo; Tang, Rentao; Tao, Jin; Wang, Xiaonan; Zheng, Baisong; Feng, Yan

2012-01-01

The conversion of renewable cellulosic biomass is of considerable interest for the production of biofuels and materials. The bottleneck in the efficient conversion is the compactness and resistance of crystalline cellulose. Carbohydrate-binding modules (CBMs), which disrupt crystalline cellulose via non-hydrolytic mechanisms, are expected to overcome this bottleneck. However, the lack of convenient methods for quantitative analysis of the disruptive functions of CBMs have hindered systematic studies and molecular modifications. Here we established a practical and systematic platform for quantifying and comparing the non-hydrolytic disruptive activities of CBMs via the synergism of CBMs and a catalytic module within designed chimeric cellulase molecules. Bioinformatics and computational biology were also used to provide a deeper understanding. A convenient vector was constructed to serve as a cellulase matrix into which heterologous CBM sequences can be easily inserted. The resulting chimeric cellulases were suitable for studying disruptive functions, and their activities quantitatively reflected the disruptive functions of CBMs on crystalline cellulose. In addition, this cellulase matrix can be used to construct novel chimeric cellulases with high hydrolytic activities toward crystalline cellulose. PMID:22778256

Heterogeneous Reactions of Limonene on Mineral Dust: Impacts of Adsorbed Water and Nitric Acid.

Science.gov (United States)

Lederer, Madeline R; Staniec, Allison R; Coates Fuentes, Zoe L; Van Ry, Daryl A; Hinrichs, Ryan Z

2016-12-08

Biogenic volatile organic compounds (BVOCs), including the monoterpene limonene, are a major source of secondary organic aerosol (SOA). While gas-phase oxidation initiates the dominant pathway for BVOC conversion to SOA, recent studies have demonstrated that biogenic hydrocarbons can also directly react with acidic droplets. To investigate whether mineral dust may facilitate similar reactive uptake of biogenic hydrocarbons, we studied the heterogeneous reaction of limonene with mineral substrates using condensed-phase infrared spectroscopy and identified the formation of irreversibly adsorbed organic products. For kaolinite, Arizona Test Dust, and silica at 30% relative humidity, GC-MS identified limonene-1,2-diol as the dominant product with total organic surface concentrations on the order of (3-5) × 10 18 molecules m -2 . Experiments with 18 O-labeled water support a mechanism initiated by oxidation of limonene by surface redox sites forming limonene oxide followed by water addition to the epoxide to form limonenediol. Limonene uptake on α-alumina, γ-alumina, and montmorillonite formed additional products in high yield, including carveol, carvone, limonene oxide, and α-terpineol. To model tropospheric processing of mineral aerosol, we also exposed each mineral substrate to gaseous nitric acid prior to limonene uptake and identified similar surface adsorbed products that were formed at rates 2 to 5 times faster than without nitrate coatings. The initial rate of reaction was linearly dependent on gaseous limonene concentration between 5 × 10 12 and 5 × 10 14 molecules cm -3 (0.22-20.5 ppm) consistent with an Eley-Rideal-type mechanism in which gaseous limonene reacts directly with reactive surface sites. Increasing relative humidity decreased the amount of surface adsorbed products indicating competitive adsorption of surface adsorbed water. Using a laminar flow tube reactor we measured the uptake coefficient for limonene on kaolinite at 25% RH to range from

Production of certain hydrolytic enzymes by psychrophilic bacteria from the Antarctic krill, zooplankton and seawater

Digital Repository Service at National Institute of Oceanography (India)

Ramaiah, N.

of hydrolytic enzymes compared to those strains collected either from water or krill samples. Based on these results, the functional role of bacterial enzymes in relation to trophodynamics of euphausiids and their role in the post-harvest technology of krill...

Modeling multicomponent ionic transport in groundwater with IPhreeqc coupling: Electrostatic interactions and geochemical reactions in homogeneous and heterogeneous domains

DEFF Research Database (Denmark)

Muniruzzaman, Muhammad; Rolle, Massimo

2016-01-01

is coupled with the geochemical code PHREEQC-3 by utilizing the IPhreeqc module, thus enabling to perform the geochemical calculations included in the PHREEQC's reaction package. The multicomponent reactive transport code is benchmarked with different 1-D and 2-D transport problems. Successively...... the electrostatic interactions during transport of charged ions in physically and chemically heterogeneous porous media. The modeling approach is based on the local charge balance and on the description of compound-specific and spatially variable diffusive/dispersive fluxes. The multicomponent ionic transport code......, conservative and reactive transport examples are presented to demonstrate the capability of the proposed model to simulate transport of charged species in heterogeneous porous media with spatially variable physical and chemical properties. The results reveal that the Coulombic cross-coupling between dispersive...

Light-induced heterogeneous reactions of NO2 on indoor surfaces: How they affect the balance of nitrous acid

Science.gov (United States)

Gomez Alvarez, E.; Soergel, M.; Bassil, S.; Zetzsch, C.; Gligorovski, S.; Wortham, H.

2011-12-01

Nitrous acid (HONO) is an important indoor pollutant. The adverse health effects due to the formation of nitrosamines are well known. HONO acts as a nitrosating agent after wall reactions of HONO with nicotine [Sleiman et al., 2010]. Indoor air can be surprisingly rich in HONO (homes with fireplaces, stoves, gas heating and cooking) and also surfaces are abundant. High HONO concentrations have been measured in indoor environments, from the direct emissions and heterogeneous reactions of NO2 in darkness. However, the measured HONO concentrations do not correspond to the HONO levels determined by the models [Carslaw, 2007]. We have tested in a flow tube reactor on-line coupled to a NOx analyzer and a sensitive Long Path Absorption Photometry instrument, the behaviour of various indoor surfaces towards NO2 under simulated solar light irradiation (λ= 300-700 nm). Our study has allowed us to obtain a deeper knowledge on the mechanisms of heterogeneous formation of HONO, quantifying the dependence of HONO formation on behalf of NO2 concentration and relative humidity and the enhancement of HONO formation in the presence of light. Pyrex, acidic detergent, alkaline detergent, paint and lacquer were tested on behalf of their heterogeneous reactivity towards NO2 in the absence and in presence of light. The results obtained demonstrated that indoor surfaces are photo-chemically active under atmospherically relevant conditions. The strongly alkaline surfaces (such as certain types of detergent) show a strong long-term uptake capacity. However, other surfaces such as detergents with a more acidic character released HONO. In some cases such as paint and varnish, a strong HONO release with light was detected, which was significantly higher than that obtained over clean glass surfaces. Certain organics present on their composition could exert a photo-sensitizing effect that may explain their increased reactivity. Unfortunately, the final balance points towards an important net

Halophilic Bacteria as a Source of Novel Hydrolytic Enzymes

Science.gov (United States)

de Lourdes Moreno, María; Pérez, Dolores; García, María Teresa; Mellado, Encarnación

2013-01-01

Hydrolases constitute a class of enzymes widely distributed in nature from bacteria to higher eukaryotes. The halotolerance of many enzymes derived from halophilic bacteria can be exploited wherever enzymatic transformations are required to function under physical and chemical conditions, such as in the presence of organic solvents and extremes in temperature and salt content. In recent years, different screening programs have been performed in saline habitats in order to isolate and characterize novel enzymatic activities with different properties to those of conventional enzymes. Several halophilic hydrolases have been described, including amylases, lipases and proteases, and then used for biotechnological applications. Moreover, the discovery of biopolymer-degrading enzymes offers a new solution for the treatment of oilfield waste, where high temperature and salinity are typically found, while providing valuable information about heterotrophic processes in saline environments. In this work, we describe the results obtained in different screening programs specially focused on the diversity of halophiles showing hydrolytic activities in saline and hypersaline habitats, including the description of enzymes with special biochemical properties. The intracellular lipolytic enzyme LipBL, produced by the moderately halophilic bacterium Marinobacter lipolyticus, showed advantages over other lipases, being an enzyme active over a wide range of pH values and temperatures. The immobilized LipBL derivatives obtained and tested in regio- and enantioselective reactions, showed an excellent behavior in the production of free polyunsaturated fatty acids (PUFAs). On the other hand, the extremely halophilic bacterium, Salicola marasensis sp. IC10 showing lipase and protease activities, was studied for its ability to produce promising enzymes in terms of its resistance to temperature and salinity. PMID:25371331

Halophilic Bacteria as a Source of Novel Hydrolytic Enzymes

Directory of Open Access Journals (Sweden)

Encarnación Mellado

2013-01-01

Full Text Available Hydrolases constitute a class of enzymes widely distributed in nature from bacteria to higher eukaryotes. The halotolerance of many enzymes derived from halophilic bacteria can be exploited wherever enzymatic transformations are required to function under physical and chemical conditions, such as in the presence of organic solvents and extremes in temperature and salt content. In recent years, different screening programs have been performed in saline habitats in order to isolate and characterize novel enzymatic activities with different properties to those of conventional enzymes. Several halophilic hydrolases have been described, including amylases, lipases and proteases, and then used for biotechnological applications. Moreover, the discovery of biopolymer-degrading enzymes offers a new solution for the treatment of oilfield waste, where high temperature and salinity are typically found, while providing valuable information about heterotrophic processes in saline environments. In this work, we describe the results obtained in different screening programs specially focused on the diversity of halophiles showing hydrolytic activities in saline and hypersaline habitats, including the description of enzymes with special biochemical properties. The intracellular lipolytic enzyme LipBL, produced by the moderately halophilic bacterium Marinobacter lipolyticus, showed advantages over other lipases, being an enzyme active over a wide range of pH values and temperatures. The immobilized LipBL derivatives obtained and tested in regio- and enantioselective reactions, showed an excellent behavior in the production of free polyunsaturated fatty acids (PUFAs. On the other hand, the extremely halophilic bacterium, Salicola marasensis sp. IC10 showing lipase and protease activities, was studied for its ability to produce promising enzymes in terms of its resistance to temperature and salinity.

PMMA/Ca2+ bone cements. Hydrolytic properties and bioactivity

Directory of Open Access Journals (Sweden)

Mónica L. Hernández

2012-01-01

Full Text Available Bone cements of poly (methyl methacrylate (PMMA have been used for about 40 years to fix artificial prosthesis to bone structure. The aim of this study was to evaluate the absorption, solubility, degradation and bioactivity of novel formulations of PMMA/Ca2+ bone cements. These properties were evaluated using a fractional experimental design. Hydrolytic parameters were determined, from which we found that 7/8 of the formulations for absorption and 6/8 for solubility fulfill the ISO 4049:2000 requirements. The final degradation values ranged between 1 and 5%, except for one of the formulations. Besides, some formulations showed bioactivity after seven days of immersion in SBF solution.

Ultra-Small Fatty Acid-Stabilized Magnetite Nanocolloids Synthesized by In Situ Hydrolytic Precipitation

Directory of Open Access Journals (Sweden)

Kheireddine El-Boubbou

2015-01-01

Full Text Available Simple, fast, large-scale, and cost-effective preparation of uniform controlled magnetic nanoparticles remains a major hurdle on the way towards magnetically targeted applications at realistic technical conditions. Herein, we present a unique one-pot approach that relies on simple basic hydrolytic in situ coprecipitation of inexpensive metal salts (Fe2+ and Fe3+ compartmentalized by stabilizing fatty acids and aided by the presence of alkylamines. The synthesis was performed at relatively low temperatures (~80°C without the use of high-boiling point solvents and elevated temperatures. This method allowed for the production of ultra-small, colloidal, and hydrophobically stabilized magnetite metal oxide nanoparticles readily dispersed in organic solvents. The results reveal that the obtained magnetite nanoparticles exhibit narrow size distributions, good monodispersities, high saturation magnetizations, and excellent colloidal stabilities. When the [fatty acid] : [Fe] ratio was varied, control over nanoparticle diameters within the range of 2–10 nm was achieved. The amount of fatty acid and alkylamine used during the reaction proved critical in governing morphology, dispersity, uniformity, and colloidal stability. Upon exchange with water-soluble polymers, the ultra-small sized particles become biologically relevant, with great promise for theranostic applications as imaging and magnetically targeted delivery vehicles.

Vanishing microwave effects : influence of heterogeneity

NARCIS (Netherlands)

Dressen, M.H.C.L.; Kruijs, van de B.H.P.; Meuldijk, J.; Vekemans, J.A.J.M.; Hulshof, L.A.

2007-01-01

A consistent setup of experiments has been conducted to demonstrate an enhanced reaction rate under microwave irradiation as compared to conventional heating, i.e. a real microwave effect. It was found that addition of a cosolvent, diminishing the heterogeneous character of the reaction mixture,

Heterogeneous continuous-time random walks

Science.gov (United States)

Grebenkov, Denis S.; Tupikina, Liubov

2018-01-01

We introduce a heterogeneous continuous-time random walk (HCTRW) model as a versatile analytical formalism for studying and modeling diffusion processes in heterogeneous structures, such as porous or disordered media, multiscale or crowded environments, weighted graphs or networks. We derive the exact form of the propagator and investigate the effects of spatiotemporal heterogeneities onto the diffusive dynamics via the spectral properties of the generalized transition matrix. In particular, we show how the distribution of first-passage times changes due to local and global heterogeneities of the medium. The HCTRW formalism offers a unified mathematical language to address various diffusion-reaction problems, with numerous applications in material sciences, physics, chemistry, biology, and social sciences.

Optimization of Acid Orange 7 Degradation in Heterogeneous Fenton-like Reaction Using Fe3-xCoxO4 Catalyst

Science.gov (United States)

Ibrahim, M. Z.; Alrozi, R.; Zubir, N. A.; Bashah, N. A.; Ali, S. A. Md; Ibrahim, N.

2018-05-01

The oxidation process such as heterogeneous Fenton and/or Fenton-like reactions is considered as an effective and efficient method for treatment of dye degradation. In this study, the degradation of Acid Orange 7 (AO7) was investigated by using Fe3-xCoxO4 as a heterogeneous Fenton-like catalyst. Response surface methodology (RSM) was used to optimize the operational parameters condition and the interaction of two or more parameters. The parameter studies were catalyst dosage (X1 ), pH (X2 ) and H2O2 concentration (X3 ) towards AO7 degradation. Based on analysis of variance (ANOVA), the derived quadratic polynomial model was significant whereby the predicted values matched the experimental values with regression coefficient of R2 = 0.9399. The optimum condition for AO7 degradation was obtained at catalyst dosage of 0.84 g/L, pH of 3 and H2O2 concentration of 46.70 mM which resulted in 86.30% removal of AO7 dye. These findings present new insights into the influence of operational parameters in the heterogeneous Fenton-like oxidation of AO7 using Fe3-xCoxO4 catalyst.

In-situ characterization of heterogeneous catalysts

CERN Document Server

Rodriguez, Jose A; Chupas, Peter J

2013-01-01

Helps researchers develop new catalysts for sustainable fuel and chemical production Reviewing the latest developments in the field, this book explores the in-situ characterization of heterogeneous catalysts, enabling readers to take full advantage of the sophisticated techniques used to study heterogeneous catalysts and reaction mechanisms. In using these techniques, readers can learn to improve the selectivity and the performance of catalysts and how to prepare catalysts as efficiently as possible, with minimum waste. In-situ Characterization of Heterogeneous Catalysts feat

The effect of oxidation on the enzyme-catalyzed hydrolytic biodegradation of poly(urethane)s.

Science.gov (United States)

Labow, Rosalind S; Tang, Yiwen; McCloskey, Christopher B; Santerre, J Paul

2002-01-01

Although the biodegradation of polyurethanes (PU) by oxidative and hydrolytic agents has been studied extensively, few investigations have reported on the combination of their effects. Since neutrophils (PMN) arrive at an implanted device first and release HOCl, followed by monocyte-derived macrophages (MDM) which have potent esterase activities and oxidants of their own, the combined effect of oxidative and hydrolytic degradation on radiolabeled polycarbonate-polyurethanes (PCNU)s was investigated and compared to that of a polyester-PU (PESU) and a polyether-PU (PEU). The PCNUs were synthesized with PCN (MW = 1,000), and butanediol (14C-BD) and one of two diisocyanates, hexane-1,6-diisocyanate (14C-HDI) or methylene bis-p-phenyl diisocyanate (MDI). The PESU and PEU were synthesized using toluene-diisocyanate (14C-TDI), with polycaprolactone and polytetramethylene oxide as soft segments respectively, and ethylene diamine as the chain extender. The effect of pre-treatment with 0.1 mM HOC1 for 1 week on the HDI-based PCNUs and both TDI-based PUs resulted in a significant inhibition of radiolabel release (RR) elicited by cholesterol esterase (CE), when compared to buffer alone, whereas the MDI-based PCNU showed a small but significant increase. When PMN were activated on the HDI-based PCNU surface with phorbol myristate acetate (PMA), HOCl was released for 3 h, and was almost completely abolished by sodium azide (AZ). Simultaneously, the PMN-elicited RR, shown previously to be due to the esterolytic cleavage by serine proteases, was inhibited approximately 75% by PMA-activation of the cells, but significantly increased relative to the latter when AZ was added. Both in vitro oxidation by HOCl and the release of HOCI by PMN were associated with the inhibition of RR and suggest perturbations between oxidative and hydrolytic mechanisms of biodegradation.

Converting homogeneous to heterogeneous in electrophilic catalysis using monodisperse metal nanoparticles.

Science.gov (United States)

Witham, Cole A; Huang, Wenyu; Tsung, Chia-Kuang; Kuhn, John N; Somorjai, Gabor A; Toste, F Dean

2010-01-01

A continuing goal in catalysis is to unite the advantages of homogeneous and heterogeneous catalytic processes. To this end, nanoparticles represent a new frontier in heterogeneous catalysis, where this unification can also be supplemented by the ability to obtain new or divergent reactivity and selectivity. We report a novel method for applying heterogeneous catalysts to known homogeneous catalytic reactions through the design and synthesis of electrophilic platinum nanoparticles. These nanoparticles are selectively oxidized by the hypervalent iodine species PhICl(2), and catalyse a range of π-bond activation reactions previously only catalysed through homogeneous processes. Multiple experimental methods are used to unambiguously verify the heterogeneity of the catalytic process. The discovery of treatments for nanoparticles that induce the desired homogeneous catalytic activity should lead to the further development of reactions previously inaccessible in heterogeneous catalysis. Furthermore, a size and capping agent study revealed that Pt PAMAM dendrimer-capped nanoparticles demonstrate superior activity and recyclability compared with larger, polymer-capped analogues.

Converting Homogeneous to Heterogeneous in Electrophilic Catalysis using Monodisperse Metal Nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Witham, Cole A.; Huang, Wenyu; Tsung, Chia-Kuang; Kuhn, John N.; Somorjai, Gabor A.; Toste, F. Dean

2009-10-15

A continuing goal in catalysis is the transformation of processes from homogeneous to heterogeneous. To this end, nanoparticles represent a new frontier in heterogeneous catalysis, where this conversion is supplemented by the ability to obtain new or divergent reactivity and selectivity. We report a novel method for applying heterogeneous catalysts to known homogeneous catalytic reactions through the design and synthesis of electrophilic platinum nanoparticles. These nanoparticles are selectively oxidized by the hypervalent iodine species PhICl{sub 2}, and catalyze a range of {pi}-bond activation reactions previously only homogeneously catalyzed. Multiple experimental methods are utilized to unambiguously verify the heterogeneity of the catalytic process. The discovery of treatments for nanoparticles that induce the desired homogeneous catalytic activity should lead to the further development of reactions previously inaccessible in heterogeneous catalysis. Furthermore, our size and capping agent study revealed that Pt PAMAM dendrimer-capped nanoparticles demonstrate superior activity and recyclability compared to larger, polymer-capped analogues.

Influence of preparation conditions of hollow titania–nickel composite spheres on their catalytic activity for hydrolytic dehydrogenation of ammonia borane

Energy Technology Data Exchange (ETDEWEB)

Umegaki, Tetsuo, E-mail: umegaki.tetsuo@nihon-u.ac.jp [Department of Materials and Applied Chemistry, College of Science and Technology, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8308 (Japan); Ohashi, Takato [Department of Materials and Applied Chemistry, College of Science and Technology, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8308 (Japan); Xu, Qiang [National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577 (Japan); Kojima, Yoshiyuki [Department of Materials and Applied Chemistry, College of Science and Technology, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8308 (Japan)

2014-04-01

Highlights: • We study influence of preparation conditions on activity of hollow titania–nickel composite spheres. • The activity for hydrolytic dehydrogenation of NH{sub 3}BH{sub 3} increases with increase of Ti + Ni content. • The activity depends on the amount of PS residue in the hollow spheres. - Abstract: The present work reports influence of preparation conditions of hollow titania–nickel composite spheres on their morphology and catalytic activity for hydrolytic dehydrogenation of ammonia borane (NH{sub 3}BH{sub 3}). The as-prepared hollow titania–nickel composite spheres were characterized by transmission electron microscopy (TEM). Catalytic activities of the hollow spheres for hydrolytic dehydrogenation of aqueous NaBH{sub 4}/NH{sub 3}BH{sub 3} solution improve with the decrease of Ti + Ni content. From the results of FTIR spectra and elemental analysis, the amount of residual polystyrene (PS) templates is able to be reduced by increasing aging time for the preparation, and the catalytic activity of the hollow spheres increases when the amount of residual PS templates decreases. The carbon content in the hollow spheres prepared with aging time = 24 h is 17.3 wt.%, and the evolution of 62 mL hydrogen is finished in about 22 min in the presence of the hollow spheres from aqueous NaBH{sub 4}/NH{sub 3}BH{sub 3} solution. The molar ratio of the hydrolytically generated hydrogen to the initial NH{sub 3}BH{sub 3} in the presence of the hollow spheres is 2.7.

The contribution of vanadium and titanium on improving methylene blue decolorization through heterogeneous UV-Fenton reaction catalyzed by their co-doped magnetite

International Nuclear Information System (INIS)

Liang, Xiaoliang; Zhong, Yuanhong; Zhu, Sanyuan; Ma, Lingya; Yuan, Peng; Zhu, Jianxi; He, Hongping; Jiang, Zheng

2012-01-01

Highlights: ► Ti-V co-doped magnetite has strong catalytic activity in UV-Fenton reaction. ► Ti 4+ is more positive to adsorption and catalytic activity of magnetite than V 3+ . ► Mechanism of substitution increasing the adsorption and catalytic activity. ► The obtained results are benefit for application of magnetite in treating wastewater. - Abstract: This study investigated the methylene blue (MB) decolorization through heterogeneous UV-Fenton reaction catalyzed by V-Ti co-doped magnetites, with emphasis on comparing the contribution of V and Ti cations on improving the adsorption and catalytic activity of magnetite. In the well crystallized spinel structure, both Ti 4+ and V 3+ occupied the octahedral sites. Ti 4+ showed a more obvious effect on increasing specific surface area and superficial hydroxyl amount than V 3+ did, resulting in a significant improvement of the adsorption ability of magnetite to MB. The UV introduction greatly accelerated MB degradation. And magnetite with more Ti and less V displayed better catalytic activity in MB degradation through heterogeneous UV-Fenton reaction. The transformation of degradation products and individual contribution from vanadium and titanium on improving adsorption and catalytic activity of magnetite were also investigated. These new insights are of high importance for well understanding the interface interaction between contaminants and metal doped magnetites, and the environmental application of natural and synthetic magnetites.

Biochar amendment to lead-contaminated soil: Effects on fluorescein diacetate hydrolytic activity and phytotoxicity to rice.

Science.gov (United States)

Tan, Xiaofei; Liu, Yunguo; Gu, Yanling; Zeng, Guangming; Hu, Xinjiang; Wang, Xin; Hu, Xi; Guo, Yiming; Zeng, Xiaoxia; Sun, Zhichao

2015-09-01

The amendment effects of biochar on total microbial activity was measured by fluorescein diacetate (FDA) hydrolytic activity, and phytotoxicity in Pb(II)-contaminated soils was examined by the application of 4 different biochars to soil, with rice as a test plant. The FDA hydrolytic activities of biochar-amended soils were much higher than that of the control. The survival rate of rice in lead-contaminated biochar-amended soils showed significant improvement over the control, especially for bamboo biochar-amended soil (93.3%). In addition, rice grown in lead-contaminated control sediment displayed lower biomass production than that in biochar-amended soil. The immobilization of Pb(II) and the positive effects of biochar amendment on soil microorganisms may account for these effects. The results suggest that biochar may have an excellent ability to mitigate the toxic effects of Pb(II) on soil microorganisms and rice. © 2015 SETAC.

Measuring Heterogeneous Reaction Rates with ATR-FTIR Spectroscopy to Evaluate Chemical Fates in an Atmospheric Environment: A Physical Chemistry and Environmental Chemistry Laboratory Experiment

Science.gov (United States)

Roberts, Jason E.; Zeng, Guang; Maron, Marta K.; Mach, Mindy; Dwebi, Iman; Liu, Yong

2016-01-01

This paper reports an undergraduate laboratory experiment to measure heterogeneous liquid/gas reaction kinetics (ozone-oleic acid and ozone-phenothrin) using a flow reactor coupled to an attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectrometer. The experiment is specially designed for an upper-level undergraduate Physical…

Borostannylation of Alkynes and Enynes. Scope and Limitations of the Reaction and Utility of the Adducts

Science.gov (United States)

Singidi, Ramakrishna Reddy; RajanBabu, T. V.

2010-01-01

The utility of the bis-metallating reagent 1,3-dimethyl-2-trimethylstannyl-2-bora-1,3-diazacyclopentane (1) has not been fully realized because of the hydrolytic instability of the products derived from catalyzed vicinal syn-additions to alkynes. The isolation of variety of such adducts derived from alkynes (and also from hitherto unreported additions to 1,3-enynes) as stable boron pinacolates is reported. Examples of the applications of resulting products in tandem cross-coupling reactions and as dienes in Diels-Alder reactions are illustrated. PMID:20459076

Volatility and lifetime against OH heterogeneous reaction of ambient isoprene-epoxydiols-derived secondary organic aerosol (IEPOX-SOA)

Energy Technology Data Exchange (ETDEWEB)

Hu, Weiwei; Palm, Brett B.; Day, Douglas A.; Campuzano-Jost, Pedro; Krechmer, Jordan E.; Peng, Zhe; de Sá, Suzane S.; Martin, Scot T.; Alexander, M. Lizabeth; Baumann, Karsten; Hacker, Lina; Kiendler-Scharr, Astrid; Koss, Abigail R.; de Gouw, Joost A.; Goldstein, Allen H.; Seco, Roger; Sjostedt, Steven J.; Park, Jeong-Hoo; Guenther, Alex B.; Kim, Saewung; Canonaco, Francesco; Prévôt, André S. H.; Brune, William H.; Jimenez, Jose L.

2016-01-01

Isoprene-epoxydiols-derived secondary organic aerosol (IEPOX-SOA) can contribute substantially to organic aerosol (OA) concentrations in forested areas under low NO conditions, hence significantly influencing the regional and global OA budgets, accounting, for example, for 16–36 % of the submicron OA in the southeastern United States (SE US) summer. Particle evaporation measurements from a thermodenuder show that the volatility of ambient IEPOX-SOA is lower than that of bulk OA and also much lower than that of known monomer IEPOX-SOA tracer species, indicating that IEPOX-SOA likely exists mostly as oligomers in the aerosol phase. The OH aging process of ambient IEPOX-SOA was investigated with an oxidation flow reactor (OFR). New IEPOX-SOA formation in the reactor was negligible, as the OFR does not accelerate processes such as aerosol uptake and reactions that do not scale with OH. Simulation results indicate that adding ~100 µg m^-3 of pure H₂SO₄ to the ambient air allows IEPOX-SOA to be efficiently formed in the reactor. The heterogeneous reaction rate coefficient of ambient IEPOX-SOA with OH radical (k_OH) was estimated as 4.0 ± 2.0 ×10^-13 cm³ molec^-1 s^-1, which is equivalent to more than a 2-week lifetime. A similar k_OH was found for measurements of OH oxidation of ambient Amazon forest air in an OFR. At higher OH exposures in the reactor (> 1 × 10¹² molec cm^-3 s), the mass loss of IEPOX-SOA due to heterogeneous reaction was mainly due to revolatilization of fragmented reaction products. We report, for the first time, OH reactive uptake coefficients (γ_OH = 0.59±0.33 in SE US and γ_OH = 0.68±0.38 in Amazon) for SOA under ambient conditions. A relative humidity dependence of k_OH and γ_OH was observed, consistent with surface-area-limited OH uptake

Volatility and lifetime against OH heterogeneous reaction of ambient isoprene-epoxydiols-derived secondary organic aerosol (IEPOX-SOA

Directory of Open Access Journals (Sweden)

W. Hu

2016-09-01

Full Text Available Isoprene-epoxydiols-derived secondary organic aerosol (IEPOX-SOA can contribute substantially to organic aerosol (OA concentrations in forested areas under low NO conditions, hence significantly influencing the regional and global OA budgets, accounting, for example, for 16–36 % of the submicron OA in the southeastern United States (SE US summer. Particle evaporation measurements from a thermodenuder show that the volatility of ambient IEPOX-SOA is lower than that of bulk OA and also much lower than that of known monomer IEPOX-SOA tracer species, indicating that IEPOX-SOA likely exists mostly as oligomers in the aerosol phase. The OH aging process of ambient IEPOX-SOA was investigated with an oxidation flow reactor (OFR. New IEPOX-SOA formation in the reactor was negligible, as the OFR does not accelerate processes such as aerosol uptake and reactions that do not scale with OH. Simulation results indicate that adding  ∼  100 µg m−3 of pure H2SO4 to the ambient air allows IEPOX-SOA to be efficiently formed in the reactor. The heterogeneous reaction rate coefficient of ambient IEPOX-SOA with OH radical (kOH was estimated as 4.0 ± 2.0  ×  10−13 cm3 molec−1 s−1, which is equivalent to more than a 2-week lifetime. A similar kOH was found for measurements of OH oxidation of ambient Amazon forest air in an OFR. At higher OH exposures in the reactor (>  1  ×  1012 molec cm−3 s, the mass loss of IEPOX-SOA due to heterogeneous reaction was mainly due to revolatilization of fragmented reaction products. We report, for the first time, OH reactive uptake coefficients (γOH =  0.59 ± 0.33 in SE US and γOH =  0.68 ± 0.38 in Amazon for SOA under ambient conditions. A relative humidity dependence of kOH and γOH was observed, consistent with surface-area-limited OH uptake. No decrease of kOH was observed as OH concentrations increased. These observations of physicochemical

Lignin Valorization using Heterogenous Catalytic Oxidation

DEFF Research Database (Denmark)

Melián Rodríguez, Mayra; Shunmugavel, Saravanamurugan; Kegnæs, Søren

The research interests in biomass conversion to fuels and chemicals has increased significantly in the last decade in view of current problems such as global warming, high oil prices, food crisis and other geopolitical scenarios. Many different reactions and processes to convert biomass into high...... of the reaction conditions 4. Here, we therefore present an overview of the recent research about conversion of some lignin model compounds using heterogeneous catalysis in oxidation reactions....

On the compensation effect in heterogeneous catalysis

DEFF Research Database (Denmark)

Pedersen, Thomas Bligaard; Honkala, Johanna Karoliina; Logadottir, Ashildur

2003-01-01

For a class of heterogeneously catalyzed reactions, we explain the compensation effect in terms of a switching of kinetic regimes leading to a concomitant change in the apparent activation energy and in the prefactor for the overall rate of the reaction. We first use the ammonia synthesis...

The hydrolytic stage in high solids temperature phased anaerobic digestion improves the downstream methane production rate.

Science.gov (United States)

Buffière, P; Dooms, M; Hattou, S; Benbelkacem, H

2018-07-01

The role of the hydrolytic stage in high solids temperature phased anaerobic digestion was investigated with a mixture of cattle slurry and maize silage with variable ratios (100, 70 and 30% volatile solids coming from cattle slurry). It was incubated for 48 h at 37, 55, 65 and 72 °C. Soluble chemical oxygen demand and biochemical methane potential were measured at 0, 24 and 48 h. Higher temperatures improved the amount of solubilized COD, which confirmed previously reported results. Nevertheless, solubilization mostly took place during the first 24 h. The rate of methane production in post-hydrolysis BMPs increased after 48 h hydrolysis time, but not after 24 h. The first order kinetic constant rose by 40% on average. No correlation was observed between soluble COD and downstream methane production rate, indicating a possible modification of the physical structure of the particulate solids during the hydrolytic stage. Copyright © 2018 Elsevier Ltd. All rights reserved.

Reticular Chemistry in Action: A Hydrolytically Stable MOF Capturing Twice Its Weight in Adsorbed Water

KAUST Repository

Towsif Abtab, Sk Md; Alezi, Dalal; Bhatt, Prashant; Shkurenko, Aleksander; Belmabkhout, Youssef; Aggarwal, Himanshu; Weselinski, Lukasz Jan; Alsadun, Norah Sadun; Samin, Umer; Hedhili, Mohamed N.; Eddaoudi, Mohamed

2018-01-01

Summary Hydrolytically stable adsorbents, with notable water uptake, are of prime importance and offer great potential for many water-adsorption-related applications. Nevertheless, deliberate construction of tunable porous solids with high porosity and high stability remains challenging. Here, we present the successful deployment of reticular chemistry to address this demand: we constructed Cr-soc-MOF-1, a chemically and hydrolytically stable chromium-based metal-organic framework (MOF) with underlying soc topology. Prominently, Cr-soc-MOF-1 offers the requisite thermal and chemical stability concomitant with unique adsorption properties, namely extraordinary high porosity (apparent surface area of 4,549 m2/g) affording a water vapor uptake of 1.95 g/g at 70% relative humidity. This exceptional water uptake is maintained over more than 100 adsorption-desorption cycles. Markedly, the adsorbed water can be fully desorbed by just the simple reduction of the relative humidity at 25°C. Cr-soc-MOF-1 offers great potential for use in applications pertaining to water vapor control in enclosed and confined spaces and dehumidification.

On-site hydrolytic enzymes production from fungal co-cultivation of Bermuda grass and corn cob.

Science.gov (United States)

Amaro-Reyes, Aldo; Gracida, Jorge; Huizache-Peña, Nelson; Elizondo-García, Norberto; Salazar-Martínez, José; García Almendárez, Blanca E; Regalado, Carlos

2016-07-01

Solid state fermentation (SSF) is used to produce industrial enzymes. The objective of this study was to use a co-culture of Aspergillus niger GS1 and Trichoderma reesei, grown on a mixture of Bermuda grass and corn cob to obtain fermented forage (FF) rich in hydrolytic enzymes, as a value added ingredient for animal feed. FPase, amylase and xylanase productivities (dry matter, DM) were 8.8, 181.4, and 42.1Ug(-1)h(-1), respectively (1U=reducing sugars released min(-1)), after 12-16h of SSF with C/N=60. Cellulose, hemicellulose and lignin decreased 1.6-, 2.7- and 1.9-fold (DM), respectively. In vitro ruminal and true digestibility of DM was improved 2.4- and 1.4-fold. Ruminal digestion of FF reduced 1.32-fold the acetate:propionate ratio, which may reduce the environmental impact of ruminants feeding. On-site hydrolytic enzymes productivity using SSF without enzymes extraction could be of economic potential for digestibility improvement in animal feed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Reticular Chemistry in Action: A Hydrolytically Stable MOF Capturing Twice Its Weight in Adsorbed Water

KAUST Repository

Towsif Abtab, Sk Md

2018-01-11

Summary Hydrolytically stable adsorbents, with notable water uptake, are of prime importance and offer great potential for many water-adsorption-related applications. Nevertheless, deliberate construction of tunable porous solids with high porosity and high stability remains challenging. Here, we present the successful deployment of reticular chemistry to address this demand: we constructed Cr-soc-MOF-1, a chemically and hydrolytically stable chromium-based metal-organic framework (MOF) with underlying soc topology. Prominently, Cr-soc-MOF-1 offers the requisite thermal and chemical stability concomitant with unique adsorption properties, namely extraordinary high porosity (apparent surface area of 4,549 m2/g) affording a water vapor uptake of 1.95 g/g at 70% relative humidity. This exceptional water uptake is maintained over more than 100 adsorption-desorption cycles. Markedly, the adsorbed water can be fully desorbed by just the simple reduction of the relative humidity at 25°C. Cr-soc-MOF-1 offers great potential for use in applications pertaining to water vapor control in enclosed and confined spaces and dehumidification.

Bridging heterogeneous and homogeneous catalysis concepts, strategies, and applications

CERN Document Server

Li, Can

2014-01-01

This unique handbook fills the gap in the market for an up-to-date work that links both homogeneous catalysis applied to organic reactions and catalytic reactions on surfaces of heterogeneous catalysts.

MHD Convective Flow of Jeffrey Fluid Due to a Curved Stretching Surface with Homogeneous-Heterogeneous Reactions.

Directory of Open Access Journals (Sweden)

Maria Imtiaz

Full Text Available This paper looks at the flow of Jeffrey fluid due to a curved stretching sheet. Effect of homogeneous-heterogeneous reactions is considered. An electrically conducting fluid in the presence of applied magnetic field is considered. Convective boundary conditions model the heat transfer analysis. Transformation method reduces the governing nonlinear partial differential equations into the ordinary differential equations. Convergence of the obtained series solutions is explicitly discussed. Characteristics of sundry parameters on the velocity, temperature and concentration profiles are analyzed by plotting graphs. Computations for pressure, skin friction coefficient and surface heat transfer rate are presented and examined. It is noted that fluid velocity and temperature through curvature parameter are enhanced. Increasing values of Biot number correspond to the enhancement in temperature and Nusselt number.

Hydrolytic potential of a psychrotrophic Pseudomonas isolated from refrigerated raw milk

Directory of Open Access Journals (Sweden)

Ana Paula F. Corrêa

2011-12-01

Full Text Available The production of extracellular hydrolases by a psychrotrophic bacterium isolated from refrigerated raw milk, and identified as a Pseudomonas sp. belonging to the Pseudomonas jenssenii group, was studied. This bacterium produced proteolytic and lipolytic enzymes in all media investigated (skim milk, cheese whey, casein broth, and tryptone soy broth. High levels of α-glucosidase were produced in skim milk broth. Hydrolytic enzymes detected in skim milk broth are of particular concern, indicating that these enzymes could be produced by Pseudomonas sp. during the cold storage of raw milk, contributing to the spoilage problem in milk and dairy products.

Numerical simulation for aspects of homogeneous and heterogeneous reactions in forced convection flow of nanofluid

Science.gov (United States)

Hayat, Tasawar; Shah, Faisal; Khan, Muhammad Ijaz; Alsaedi, Ahmed

2018-03-01

Mixed convection stagnation point flow of nanofluid by a vertical permeable circular cylinder has been addressed. Water is treated as ordinary liquid while nanoparticles include aluminium oxide, copper and titanium dioxide. Homogeneous-heterogeneous reactions are considered. The nonlinear higher order expressions are changed into first ordinary differential equations and then solved by built-in-Shooting method in mathematica. The results of velocity, temperature, concentration, skin friction and local Nusselt number are discussed. Our results demonstrate that surface drag force and heat transfer rate are enhanced linearly for higher estimation of curvature parameter. Further surface drag force decays for aluminium oxide and it enhances for copper nanoparticle. Heat transfer rate enhances with increasing all three types of nanoparticles. In addition, the lowest heat transfer rate is obtained in case of titanium dioxide when compared with copper and aluminium oxide.

Preparation of biodiesel from soybean oil by using heterogeneous catalyst

Energy Technology Data Exchange (ETDEWEB)

Ferdous, Kaniz; Rakib Uddin, M.; Islam, M.A. [Department of Chemical Engineering and Polymer Science, Shah Jalal University of Science and Technology, Sylhet 3114 (Bangladesh); Khan, Maksudur R. [Department of Chemical Engineering and Polymer Science, Shah Jalal University of Science and Technology, Sylhet 3114 (Bangladesh); Faculty of Chemical and Natural Resources Engineering, University Malaysia Pahang, 26300 Gambang, Kuantan, Pahang (Malaysia)

2013-07-01

The predicted shortage of fossil fuels and related environmental concerns has recently attracted significant attention to search alternative fuel. Biodiesel is one of the alternatives to fossil fuel. Now-a-days, most biodiesel is produced by the transesterification of oils using methanol and a homogeneous base catalyst. The use of homogeneous catalysts is normally limited to batch mode processing followed by a catalyst separation step. The immiscible glycerol phase, which accumulates during the course of the reaction, solubilizes the homogeneous base catalyst and therefore, withdraws from the reaction medium. Moreover, other difficulties of using homogeneous base catalysts relate to their sensitivity to free fatty acid (FFA) and water and resulting saponification phenomenon. High energy consumption and costly separation of the catalyst from the reaction mixture have inspired the use of heterogeneous catalyst. The use of heterogeneous catalysts does not lead to the formation of soaps through neutralization of FFA and saponification of oil. In the present paper, biodiesel was prepared from crude (soybean) oil by transesterification reaction using heterogeneous base catalyst name calcium oxide (CaO). Various reaction parameters were optimized and the biodiesel properties were evaluated.

A microcatalytic flow reactor for the study of heterogeneous catalytic reactions at elevated pressures

Energy Technology Data Exchange (ETDEWEB)

Belyi, A S; Fomichev, Yu V; Duplyakin, V K; Alfeev, V S

1977-07-01

A microcatalytic flow reactor for the study of heterogeneous catalytic reactions at elevated pressures (i.e., up to 40 atm) and nearly isothermal conditions up to 600/sup 0/C was designed for the conversion of small quantities of petrochemical feeds or feed mixtures at uniform, controllable flow rates of 0.5-5.0 cc/hr, for direct gas-chromatographic analysis of product samples at the reactor outlet, and for continuous monitoring of the degree of conversion in processes that evolve or absorb hydrogen. The device includes a feed injection system with a unique sealing feature that ensures a constant flow of liquid from a feed buret under positive displacement by a counterweight piston at very low rates into a tubular reactor of the perfect mixing type, a highly efficient vaporizer-mixer, and a two-channel sampler leading to the chromatograph. The apparatus has proved reliable, accurate, and convenient in two years of regular use. Diagrams.

Hydrolytic Degradation and Mechanical Stability of Poly(ε-Caprolactone)/Reduced Graphene Oxide Membranes as Scaffolds for In Vitro Neural Tissue Regeneration.

Science.gov (United States)

Sánchez-González, Sandra; Diban, Nazely; Urtiaga, Ane

2018-03-05

The present work studies the functional behavior of novel poly(ε-caprolactone) (PCL) membranes functionalized with reduced graphene oxide (rGO) nanoplatelets under simulated in vitro culture conditions (phosphate buffer solution (PBS) at 37 °C) during 1 year, in order to elucidate their applicability as scaffolds for in vitro neural regeneration. The morphological, chemical, and DSC results demonstrated that high internal porosity of the membranes facilitated water permeation and procured an accelerated hydrolytic degradation throughout the bulk pathway. Therefore, similar molecular weight reduction, from 80 kDa to 33 kDa for the control PCL, and to 27 kDa for PCL/rGO membranes, at the end of the study, was observed. After 1 year of hydrolytic degradation, though monomers coming from the hydrolytic cleavage of PCL diffused towards the PBS medium, the pH was barely affected, and the rGO nanoplatelets mainly remained in the membranes which envisaged low cytotoxic effect. On the other hand, the presence of rGO nanomaterials accelerated the loss of mechanical stability of the membranes. However, it is envisioned that the gradual degradation of the PCL/rGO membranes could facilitate cells infiltration, interconnectivity, and tissue formation.

Chemical transport reactions

CERN Document Server

Schäfer, Harald

2013-01-01

Chemical Transport Reactions focuses on the processes and reactions involved in the transport of solid or liquid substances to form vapor phase reaction products. The publication first offers information on experimental and theoretical principles and the transport of solid substances and its special applications. Discussions focus on calculation of the transport effect of heterogeneous equilibria for a gas motion between equilibrium spaces; transport effect and the thermodynamic quantities of the transport reaction; separation and purification of substances by means of material transport; and

Introduction to chemical reaction engineering

International Nuclear Information System (INIS)

Kim, Yeong Geol

1990-10-01

This deals with chemical reaction engineering with thirteen chapters. The contents of this book are introduction on reaction engineering, chemical kinetics, thermodynamics and chemical reaction, abnormal reactor, non-isothermal reactor, nonideal reactor, catalysis in nonuniform system, diffusion and reaction in porosity catalyst, design catalyst heterogeneous reactor in solid bed, a high molecule polymerization, bio reaction engineering, reaction engineering in material process, control multi-variable reactor process using digital computer.

Thermal and Hydrolytic Stability of Dithiophophoric Acids Stabilité thermique et hydrolytique des acides dithiophosphoriques

Directory of Open Access Journals (Sweden)

Ivanov S. K.

2006-11-01

Full Text Available The thermal and hydrolytic stability of dibutyl-, diisobutyl- and diisooctyldithiophosphoric acids have been studied in the range of 40-80°C. The reaction progress was followed by the H2S evolution kinetics in volumetric equipment at constant pressure, equal to the barometric one. The kinetic parameters of the process have been determined at various acid water ratios - maximum rates of gas evolution, activation energy and the kinetic order. It has been shown that the hydrolysis proceeds mainly along the sulph-hydrate group of the acid (up to temperatures of 60°C, while at higher temperatures the ester groups and the thion sulphur are attacked too. The thermal stability of dithiophosphoric acids has been studied in the presence of stainless steel, lead and copper plates. It has been shown that stainless steel doesn't affect the process rate, while copper and especially lead increase the gas evolution and decrease the activation energy. A model describing the reaction progress at the interfacial surfaces - organic phase, water and metal surface - has been developed. Based on these data a conclusion is advanced, related to the manifacture technology of antioxidant, anticorrosion and antiwear additives of the zinc dialkyldithiophosphate type. It is pointed out that the neutralization process of dithiophosphoric acids should be carried out in a stainless steel reactor at tempeatures below 70°C. Le présent article s'efforce d'élucider l'influence de l'eau, de la température et des surfaces métalliques sur la stabilité thermique et hydrolytique des acides dibutyl-, diisobutyl- et diisooctyldithiophosphoriques, à la lumière du concept d'interaction.

Thermogravimetry for optimization of chloride pyro hydrolytic separations in zirconia-magnesia matrix

International Nuclear Information System (INIS)

Pires, M.A.F.; Dantas, E.S.K.

1992-08-01

A fast and accurate method for chloride ion determination in zirconia-magnesia matrix was studied the method consists in the pyro hydrolysis of the oxides at 900 o C, using a quartz apparatus, during thirty minutes and further determination of the chloride ion collected by means of either ion-selective electrode or ion chromatography. The thermogravimetric curves (TG curves) of the metal oxides and oxychlorides provide all the information about the chloride ion evolution temperature and the influence of pyro hydrolytic accelerators (U 3 O 8 ) on ion evolution. (author)

Velocity and thermal slip effects on MHD third order blood flow in an irregular channel though a porous medium with homogeneous/ heterogeneous reactions

Science.gov (United States)

Gnaneswara Reddy, M.

2017-09-01

This communication presents the transportation of third order hydromagnetic fluid with thermal radiation by peristalsis through an irregular channel configuration filled a porous medium under the low Reynolds number and large wavelength approximations. Joule heating, Hall current and homogeneous-heterogeneous reactions effects are considered in the energy and species equations. The Second-order velocity and energy slip restrictions are invoked. Final dimensionless governing transport equations along the boundary restrictions are resolved numerically with the help of NDsolve in Mathematica package. Impact of involved sundry parameters on the non-dimensional axial velocity, fluid temperature and concentration characteristics have been analyzed via plots and tables. It is manifest that an increasing porosity parameter leads to maximum velocity in the core part of the channel. Fluid velocity boosts near the walls of the channel where as the reverse effect in the central part of the channel for higher values of first order slip. Larger values of thermal radiation parameter R reduce the fluid temperature field. Also, an increase in heterogeneous reaction parameter Ks magnifies the concentration profile. The present study has the crucial application of thermal therapy in biomedical engineering.

Kinetic study of the hydration of propylene oxide in the presence of heterogeneous catalyst

Directory of Open Access Journals (Sweden)

Akyalcin Sema

2017-01-01

Full Text Available The kinetics of the hydration of propylene oxide was studied using a pressurized batch reactor for both uncatalyzed and heterogeneously catalyzed reactions. Lewatit MonoPlus M500/HCO3 - was used as heterogeneous catalyst, which showed better performance than Dowex Marathon A/HCO3 -. The effects of the parameters, namely internal and external diffusion resistances, temperature, catalyst loading and mole ratios of reactants, on the reaction rate were studied. The uncatalyzed and heterogeneously catalyzed reactions were proven to follow a series-parallel irreversible homogeneous mechanism. The temperature dependencies of the rate constants appearing in the rate expressions were determined.

Mechanism of spiral formation in heterogeneous discretized excitable media.

Science.gov (United States)

Kinoshita, Shu-ichi; Iwamoto, Mayuko; Tateishi, Keita; Suematsu, Nobuhiko J; Ueyama, Daishin

2013-06-01

Spiral waves on excitable media strongly influence the functions of living systems in both a positive and negative way. The spiral formation mechanism has thus been one of the major themes in the field of reaction-diffusion systems. Although the widely believed origin of spiral waves is the interaction of traveling waves, the heterogeneity of an excitable medium has recently been suggested as a probable cause. We suggest one possible origin of spiral waves using a Belousov-Zhabotinsky reaction and a discretized FitzHugh-Nagumo model. The heterogeneity of the reaction field is shown to stochastically generate unidirectional sites, which can induce spiral waves. Furthermore, we found that the spiral wave vanished with only a small reduction in the excitability of the reaction field. These results reveal a gentle approach for controlling the appearance of a spiral wave on an excitable medium.

Synthesis,thermal property and hydrolytic degradation of a novel star-shaped hexa[p-(carbonylglycinomethylester)phenoxy]cyclotriphosphazene

Institute of Scientific and Technical Information of China (English)

无

2009-01-01

A novel star-shaped cyclotriphosphazene substituted by glycinomethylesterphenoxy and its intermediates are synthesized from hexachlorocyclotriphosphazene (HCCP). The structures are characterized by 1H NMR,13C NMR,31P NMR,FTIR and elemental analysis. Their thermal properties are clarified by thermogravimetric analysis (TGA),differential scanning calorimentry (DSC) and FTIR,while hydrolytic degradation behaviour is studied with UV-vis spectrophotometer and by measuring the weight loss,and the phosphorus content of residue. According to hydrolysis behaviour of hexa[p-(carbonylglycinomethylester)phenoxy]cyclotriphosphazene (HGPCP) under different conditions,it is easy to hydrolyze in hydrochloric acid (pH 1.0) than in phosphate buffer (pH 7.4) at 37℃. And the sample hydrolytic degradation still remains at the stage of side groups’ break. The TGA data show that the thermal stability of the hexa[p-(aldehyde)phenoxy]cyclotriphosphazene (HAPCP),hexa[p-(carboxyl) phenoxy]cyclotriphosphazene (HCPCP) and HGPCP is so high that their char residues are 75%,47% and 47% at 800℃,respectively,probably due to cross-linking between molecules.

Heterogeneous self-assembled media for biopolymerization

DEFF Research Database (Denmark)

Monnard, Pierre-Alain

2011-01-01

Heterogeneous media, such as micro-structured aqueous environments, could offer an alternative approach to the synthesis of biopolymers with novel functions. Structured media are here defined as specialized, self-assembled structures that are formed, e.g, by amphiphiles, such as liposomes, emulsion...... polymerization, the initial elongation rates clearly depended on the complementarity of the monomers with the templating nucleobases3. However, metal-ion catalyzed reactions deliver RNA analogs with heterogeneous linkages. Moreover, the usefulness of this medium in the form of quasi-compartmentalization extends...... beyond metal-ion catalysis reactions, as we have recently demonstrated the catalytic power of a dipeptide, SerHis, for the regioselective formation of phosphodiester bonds. These results in conjonction with the synthesis of nucleobases at -78˚C, the demonstration of ribozyme activity (RNA ligase ribozyme...

Characterization of hydrolytic degradation of polylactic acid/rice hulls composites in water at different temperatures

Directory of Open Access Journals (Sweden)

2011-02-01

Full Text Available Hydrolytic degradations of polylactic acid/rice hulls (PLA/RH composites with various rice hulls contents due to water absorptions at 23, 51 and 69°C were investigated by studying the thermal properties, chemical composition, molecular weight, and morphology of the degraded products. The results have attested that the stability of PLA/RH composites in water depends slightly on rice hulls contents but it is significantly influenced by water temperature. Water absorption in 30 days at 23°C was between 0.87 and 9.25% depending on rice hull contents. However, at thermophilic temperatures, the water absorption and degradation of these products were increased significantly. Saturations were achieved in less than 25 and 9 days at 51°C and 69°C, respectively, while hydrolytic degradation was demonstrated by an increase in fragility and development of crystallinity. At 69°C, there were significant reductions of the decomposition and glass transition temperatures of the polymer by 13°C. These changes were associated with the reduction of the molecular weight of PLA from 153.1 kDa to ~10.7 kDa due to hydrolysis of its ester group.

Non-hydrolytic sol-gel synthesis of epoxysilane-based inorganic-organic hybrid resins

International Nuclear Information System (INIS)

Jana, Sunirmal; Lim, Mi Ae; Baek, In Chan; Kim, Chang Hae; Seok, Sang Il

2008-01-01

A silica-based inorganic-organic hybrid resins (IOHR) were synthesized by non-hydrolytic sol-gel process from 3-glycidoxypropyltrimethoxysilane (GLYMO) and diphenylsilanediol (DPSD) at a fixed amount of (20 mol%) phenyltrimethoxysilane using barium hydroxide as a catalyst. The confirmation of condensation reaction in the IOHR was done by liquid state 29 Si NMR (Nuclear Magnetic Resonance) spectroscopy, measurement of viscosity as well as weight average molecular weight (W m ) of the IOHR. The W m of the IOHR was varied from 1091 to 2151, depending upon the DPSD content. Fourier transform infrared (FTIR) spectroscopic measurements were performed to investigate the details of vibrational absorption bands in the IOHR. It was seen that up to 50 mol% of DPSD there were no absorption peaks in the region of 3000-3600 cm -1 responsible for O-H groups and it reappeared at 60 mol% of DPSD due to some unreacted OH groups present in the resin. The IOHR at all the compositions was oily transparent liquid, miscible with various organic solvents like toluene, cyclohexanone, chloroform, tehrahydrofuran (THF), etc., and also commercial epoxy resins but immiscible with water. The color of the IOHR was pale yellow, which lightened with increasing DPSD content. The IOHR having 40-50 mol% of DPSD were storable. The refractive index at 632.8 nm of the resin films varied from 1.556 to 1.588, depending upon the resin composition. Physico-chemical properties such as the thermal stability, visible transparency, etc. after curing were investigated as a function of the chemical composition

Predicting Upscaled Behavior of Aqueous Reactants in Heterogeneous Porous Media

Science.gov (United States)

Wright, E. E.; Hansen, S. K.; Bolster, D.; Richter, D. H.; Vesselinov, V. V.

2017-12-01

When modeling reactive transport, reaction rates are often overestimated due to the improper assumption of perfect mixing at the support scale of the transport model. In reality, fronts tend to form between participants in thermodynamically favorable reactions, leading to segregation of reactants into islands or fingers. When such a configuration arises, reactions are limited to the interface between the reactive solutes. Closure methods for estimating control-volume-effective reaction rates in terms of quantities defined at the control volume scale do not presently exist, but their development is crucial for effective field-scale modeling. We attack this problem through a combination of analytical and numerical means. Specifically, we numerically study reactive transport through an ensemble of realizations of two-dimensional heterogeneous porous media. We then employ regression analysis to calibrate an analytically-derived relationship between reaction rate and various dimensionless quantities representing conductivity-field heterogeneity and the respective strengths of diffusion, reaction and advection.

Real-Time Monitoring of Heterogeneous Catalysis with Mass Spectrometry

Science.gov (United States)

Young, Mark A.

2009-01-01

Heterogeneous, gas-solid processes constitute an important class of catalytic reactions that play a key role in a variety of applications, such as industrial processing and environmental controls. Heterogeneous catalytic chemistry can be demonstrated in a simple heated flow reactor containing a fragment of the catalytic converter from a vehicular…

Determination of the action modes of cellulases from hydrolytic profiles over a time course using fluorescence-assisted carbohydrate electrophoresis.

Science.gov (United States)

Zhang, Qing; Zhang, Xiaomei; Wang, Peipei; Li, Dandan; Chen, Guanjun; Gao, Peiji; Wang, Lushan

2015-03-01

Fluorescence-assisted carbohydrate electrophoresis (FACE) is a sensitive and simple method for the separation of oligosaccharides. It relies on labeling the reducing ends of oligosaccharides with a fluorophore, followed by PAGE. Concentration changes of oligosaccharides following hydrolysis of a carbohydrate polymer could be quantitatively measured continuously over time using the FACE method. Based on the quantitative analysis, we suggested that FACE was a relatively high-throughput, repeatable, and suitable method for the analysis of the action modes of cellulases. On account of the time courses of their hydrolytic profiles, the apparent processivity was used to show the different action modes of cellulases. Cellulases could be easily differentiated as exoglucanases, β-glucosidases, or endoglucanases. Moreover, endoglucanases from the same glycoside hydrolases family had a variety of apparent processivity, indicating the different modes of action. Endoglucanases with the same binding capacities and hydrolytic activities had similar oligosaccharide profiles, which aided in their classification. The hydrolytic profile of Trichoderma reesei Cel12A, an endoglucanases from T. reesei, contained glucose, cellobiose, and cellotriose, which revealed that it may have a new glucosidase activity, corresponding to that of EC 3.2.1.74. A hydrolysate study of a T. reesei Cel12A-N20A mutant demonstrated that the FACE method was sufficiently sensitive to detect the influence of a single-site mutation on enzymatic activity. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Unravelling the Interactions between Hydrolytic and Oxidative Enzymes in Degradation of Lignocellulosic Biomass by Sporothrix carnis under Various Fermentation Conditions

Directory of Open Access Journals (Sweden)

Olusola A. Ogunyewo

2016-01-01

Full Text Available The mechanism underlying the action of lignocellulolytic enzymes in biodegradation of lignocellulosic biomass remains unclear; hence, it is crucial to investigate enzymatic interactions involved in the process. In this study, degradation of corn cob by Sporothrix carnis and involvement of lignocellulolytic enzymes in biodegradation were investigated over 240 h cultivation period. About 60% degradation of corn cob was achieved by S. carnis at the end of fermentation. The yields of hydrolytic enzymes, cellulase and xylanase, were higher than oxidative enzymes, laccase and peroxidase, over 144 h fermentation period. Maximum yields of cellulase (854.4 U/mg and xylanase (789.6 U/mg were at 96 and 144 h, respectively. Laccase and peroxidase were produced cooperatively with maximum yields of 489.06 U/mg and 585.39 U/mg at 144 h. Drastic decline in production of cellulase at 144 h (242.01 U/mg and xylanase at 192 h (192.2 U/mg indicates that they play initial roles in biodegradation of lignocellulosic biomass while laccase and peroxidase play later roles. Optimal degradation of corn cob (76.6% and production of hydrolytic and oxidative enzymes were achieved with 2.5% inoculum at pH 6.0. Results suggest synergy in interactions between the hydrolytic and oxidative enzymes which can be optimized for improved biodegradation.

Heterogeneous catalysis in complex, condensed reaction media

Energy Technology Data Exchange (ETDEWEB)

Cantu, David C.; Wang, Yang-Gang; Yoon, Yeohoon; Glezakou, Vassiliki-Alexandra; Rousseau, Roger; Weber, Robert S.

2017-07-01

Many reactions required for the upgrading of biomass into fuels and chemicals—hydrogenation, hydrodeoxygenation, hydrocracking—are ostensibly similar to those practiced in the upgrading of petroleum into fuels. But, repurposing hydroprocessing catalysts from refinery operations to treat bio-oil has proved to be unsatisfactory. New catalysts are needed because the composition of the biogenic reactants differs from that of petroleum-derived feedstocks (e.g. the low concentration of sulfur in cellulose-derived biomass precludes use of metal sulfide catalysts unless sulfur is added to the reaction stream). New processes are needed because bio-oils oligomerize rapidly, forming intractable coke and “gunk”, at temperatures so low that the desired upgrading reactions are impractically slow, and so low that the bio-oil upgrading must be handled as a condensed fluid. Ideally, the new catalysts and processes would exploit the properties of the multiple phases present in condensed bio-oil, notably the polarizability and structure of the fluid near a catalyst’s surface in the cybotactic region. The results of preliminary modeling of the cybotactic region of different catalyst surfaces in the hydrogenation of phenol suggest that Pd catalysts supported on hydrophilic surfaces are more active than catalysts based on lipophilic supports because the former serve to enhance the concentration of the phenol in the vicinity of the Pd. The effect stems from thermodynamics, not the rate of mass transport. This work was supported by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office. Pacific Northwest National Laboratory (PNNL) is a multiprogram national laboratory operated for DOE by Battelle.

Effect of peat extract on the hydrolytic enzymes of Phanerochaete chrysosporium

Energy Technology Data Exchange (ETDEWEB)

Nawaz, M; Gunasekaran, M

1988-08-01

Peat, a partially decomposed plant material rich in minerals and lignocellulose was tested as a substrate for the growth and production of hydrolytic enzymes viz. cellulase, cellobiase and xylanase in Phanerochaete chrysosporium. Three types of peat extracts such as cold, hot water and autoclaved were prepared and tested. Among them, autoclaved extract supported the maximal growth. The intracellular enzyme activities peaked on the fifth day after inoculation irrespective of the media and enzyme tested. Addition of cellobiose and lactose in the medium induced the production of cellulase, xylanase and to a lesser extent cellobiase. Addition of glucose and sucrose to the media resulted in the suppression of all the extracellular enzymes tested. 18 refs., 5 figs.

Saponification reaction system: a detailed mass transfer coefficient determination.

Science.gov (United States)

Pečar, Darja; Goršek, Andreja

2015-01-01

The saponification of an aromatic ester with an aqueous sodium hydroxide was studied within a heterogeneous reaction medium in order to determine the overall kinetics of the selected system. The extended thermo-kinetic model was developed compared to the previously used simple one. The reaction rate within a heterogeneous liquid-liquid system incorporates a chemical kinetics term as well as mass transfer between both phases. Chemical rate constant was obtained from experiments within a homogeneous medium, whilst the mass-transfer coefficient was determined separately. The measured thermal profiles were then the bases for determining the overall reaction-rate. This study presents the development of an extended kinetic model for considering mass transfer regarding the saponification of ethyl benzoate with sodium hydroxide within a heterogeneous reaction medium. The time-dependences are presented for the mass transfer coefficient and the interfacial areas at different heterogeneous stages and temperatures. The results indicated an important role of reliable kinetic model, as significant difference in k(L)a product was obtained with extended and simple approach.

Particle-based modeling of heterogeneous chemical kinetics including mass transfer.

Science.gov (United States)

Sengar, A; Kuipers, J A M; van Santen, Rutger A; Padding, J T

2017-08-01

Connecting the macroscopic world of continuous fields to the microscopic world of discrete molecular events is important for understanding several phenomena occurring at physical boundaries of systems. An important example is heterogeneous catalysis, where reactions take place at active surfaces, but the effective reaction rates are determined by transport limitations in the bulk fluid and reaction limitations on the catalyst surface. In this work we study the macro-micro connection in a model heterogeneous catalytic reactor by means of stochastic rotation dynamics. The model is able to resolve the convective and diffusive interplay between participating species, while including adsorption, desorption, and reaction processes on the catalytic surface. Here we apply the simulation methodology to a simple straight microchannel with a catalytic strip. Dimensionless Damkohler numbers are used to comment on the spatial concentration profiles of reactants and products near the catalyst strip and in the bulk. We end the discussion with an outlook on more complicated geometries and increasingly complex reactions.

Particle-based modeling of heterogeneous chemical kinetics including mass transfer

Science.gov (United States)

Sengar, A.; Kuipers, J. A. M.; van Santen, Rutger A.; Padding, J. T.

2017-08-01

Connecting the macroscopic world of continuous fields to the microscopic world of discrete molecular events is important for understanding several phenomena occurring at physical boundaries of systems. An important example is heterogeneous catalysis, where reactions take place at active surfaces, but the effective reaction rates are determined by transport limitations in the bulk fluid and reaction limitations on the catalyst surface. In this work we study the macro-micro connection in a model heterogeneous catalytic reactor by means of stochastic rotation dynamics. The model is able to resolve the convective and diffusive interplay between participating species, while including adsorption, desorption, and reaction processes on the catalytic surface. Here we apply the simulation methodology to a simple straight microchannel with a catalytic strip. Dimensionless Damkohler numbers are used to comment on the spatial concentration profiles of reactants and products near the catalyst strip and in the bulk. We end the discussion with an outlook on more complicated geometries and increasingly complex reactions.

The heterogeneous interaction of trace gases on mineral dust and soot: kinetics and mechanism

OpenAIRE

Karagulian, Federico; Rossi, Michel

2007-01-01

The present thesis work deals with the investigation of the heterogeneous reactions involving nitrate radical (NO3), dinitrogen pentoxide (N2O5) and ozone (O3) on surrogates of atmospheric mineral dust particles characteristic of the troposphere. An additional investigation of heterogeneous reaction of NO3 on flame soot was carried out. The goal is to characterize the kinetics (the uptake coefficient γ) as well as the reaction products. The obtained results are intended to provide reliable da...

Heterogeneous Catalysis: Deuterium Exchange Reactions of Hydrogen and Methane

Science.gov (United States)

Mirich, Anne; Miller, Trisha Hoette; Klotz, Elsbeth; Mattson, Bruce

2015-01-01

Two gas phase deuterium/hydrogen exchange reactions are described utilizing a simple inexpensive glass catalyst tube containing 0.5% Pd on alumina through which gas mixtures can be passed and products collected for analysis. The first of these exchange reactions involves H[subscript 2] + D[subscript 2], which proceeds at temperatures as low as 77…

Fabrication of hollow silica–zirconia composite spheres and their activity for hydrolytic dehydrogenation of ammonia borane

Energy Technology Data Exchange (ETDEWEB)

Umegaki, Tetsuo, E-mail: umegaki.tetsuo@nihon-u.ac.jp [Department of Materials and Applied Chemistry, College of Science and Engineering, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8308 (Japan); Hosoya, Tatsuya; Toyama, Naoki [Department of Materials and Applied Chemistry, College of Science and Engineering, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8308 (Japan); Xu, Qiang [National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577 (Japan); Kojima, Yoshiyuki [Department of Materials and Applied Chemistry, College of Science and Engineering, Nihon University, 1-8-14, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8308 (Japan)

2014-09-01

Highlights: • Hollow silica–zirconia composite spheres were fabricated on polystyrene templates by the sol–gel method. • We study the effect of preparation conditions on the activity for hydrolytic dehydrogenation of ammonia borane. • The activity of hollow silica–zirconia composite spheres depends on wall thickness. - Abstract: In this paper, we report fabrication of hollow silica–zirconia composite spheres by polystyrene (PS) template method and control of wall thickness of the hollow spheres in nanoscale. Both the hollow spheres before and after calcination were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), elemental analysis, and powder X-ray diffraction analysis (XRD). Morphology of the hollow spheres does not significantly change after calcination from the results of SEM and TEM images, while the amount of residual PS templates drastically decreases via the calcination procedure from the results of FTIR and elemental analysis. The sample after calcination mainly includes amorphous silica from the results of XRD, indicating that the hollow silica–zirconia composite spheres consist of amorphous phases and/or fine particles. Wall thicknesses of the samples after calcination are controlled by adjusting the amount of PS template suspension, and hollow silica–zirconia composite spheres with the wall thicknesses of 17.5, 15.0, 10.0, and 2.0 nm are obtained using the PS template suspension of 25.0, 33.5, 100.0, and 400.0 g, respectively. The activities of the hollow spheres for hydrolytic dehydrogenation of ammonia borane (NH{sub 3}BH{sub 3}) were compared. The evolutions of 2.0, 3.1, 5.0, and 8.0 mL hydrogen from aqueous NH{sub 3}BH{sub 3} solution were finished in about 4, 5, 3, and 7 min in the presence of the hollow spheres with wall thicknesses of 17.5, 15.0, 10.0, and 2.0 nm, respectively. The molar ratios of the hydrolytically generated hydrogen to

Graphene: a promising two-dimensional support for heterogeneous catalysts

Directory of Open Access Journals (Sweden)

Xiaobin eFan

2015-01-01

Full Text Available Graphene has many advantages that make it an attractive two-dimensional (2D support for heterogeneous catalysts. It not only allows the high loading of targeted catalytic species, but also facilitates the mass transfer during the reaction processes. These advantages, along with its unique physical and chemical properties, endow graphene great potential as catalyst support in heterogeneous catalysis.

The Mineralogic Transformation of Ferrihydrite Induced by Heterogeneous Reaction with Bioreduced Anthraquinone Disulfonate (AQDS) and the Role of Phosphate

Energy Technology Data Exchange (ETDEWEB)

Zachara, John M.; Kukkadapu, Ravi K.; Peretyazhko, Tetyana; Bowden, Mark E.; Wang, Chong M.; Kennedy, David W.; Moore, Dean A.; Arey, Bruce W.

2011-10-12

Anthraquinone-2-6-disulfonate (AQDS) enhances electron donor utilization and mineral product crystallization in studies of Fe(III) oxide reductive mineralization by metal reducing bacteria (MRB) through heterogeneous redox reaction. In spite of the strong effect of AQDS in these systems, little information exits on its direct role in reductive mineralization. To provide such insights, bioreduced AQDS (AH2DS; dihydro-anthraquinone) was reacted with a 2-line, Si-substituted ferrihydrite under anoxic conditions at neutral pH in PIPES buffer. Phosphate (P) and bicarbonate (C); common adsorptive oxyanions and media/buffer components known to effect ferrihydrite mineralization; and Fe(II)aq (as a catalytic mineralization agent) were used in comparative experiments. Heterogeneous AH2DS oxidation coupled with Fe(III) reduction occurred within 0.13-1 day, with mineralogic transformation occurring thereafter. The product suite included lepidocrocite, goethite, and/or magnetite, with proportions varing with reductant:oxidant ratio (r:o) and the presence of P or C. Lepidocrocite was the primary product at low r:o in the absence of P or C, with evidence for multiple formation pathways. P inhibited reductive recrystallization, while C promoted goethite formation. Stoichiometric magnetite was the sole product at higher r:o in the absence and presence of P. Lepidocrocite was the primary mineralization product in the Fe(II)aq system, with magnetite observed at near equal amounts when Fe(II) was high [Fe(II)/Fe(III)]=0.5 and P was absent. P had a greater effect on reductive mineralization in the Fe(II)aq system, while AQDS was more effective than Fe(II)aq in promoting magnetite formation. The direct AH2DS-driven reductive reaction pathway produced mineral products that were different from AH2DS-ferrihydite-MRB systems, particularly in presence of P.

Hydrolytically stable fluorinated metal-organic frameworks for energy-efficient dehydration

KAUST Repository

Cadiau, Amandine

2017-05-18

Natural gas must be dehydrated before it can be transported and used, but conventional drying agents such as activated alumina or inorganic molecular sieves require an energy-intensive desiccant-regeneration step. We report a hydrolytically stable fluorinated metal-organic framework, AlFFIVE-1-Ni (KAUST-8), with a periodic array of open metal coordination sites and fluorine moieties within the contracted square-shaped one-dimensional channel. This material selectively removed water vapor from gas streams containing CO2, N2, CH4, and higher hydrocarbons typical of natural gas, as well as selectively removed both H2O and CO2 in N2-containing streams. The complete desorption of the adsorbed water molecules contained by the AlFFIVE-1-Ni sorbent requires relatively moderate temperature (~105°C) and about half the energy input for commonly used desiccants.

Variation in pH Optima of Hydrolytic Enzyme Activities in Tropical Rain Forest Soils ▿

OpenAIRE

Turner, Benjamin L.

2010-01-01

Extracellular enzymes synthesized by soil microbes play a central role in the biogeochemical cycling of nutrients in the environment. The pH optima of eight hydrolytic enzymes involved in the cycles of carbon, nitrogen, phosphorus, and sulfur, were assessed in a series of tropical forest soils of contrasting pH values from the Republic of Panama. Assays were conducted using 4-methylumbelliferone-linked fluorogenic substrates in modified universal buffer. Optimum pH values differed markedly am...

Cell heterogeneity problems in the analysis of zero power experiments

International Nuclear Information System (INIS)

Grimstone, M.J.; Stevenson, J.M.

1979-01-01

Methods are described for treating plate and pin cell heterogeneity in the preparation of broad group cross-sections used in the analysis of zero power fast reactor experiments. Methods used at Karlsruhe and Winfrith are summarised and compared, with particular reference to the treatment of resonance shielding, the calculation of broad group spatial fine structure, the treatment of leakage and the calculation of anisotropic diffusion coefficients. The problems of cells near boundaries such as core-breeder interfaces and of singularities such as control rods are also considered briefly. Numerical studies carried out to investigate approximations in the methods are described. These include tests of the accuracy of one-dimensional cell modelling techniques, and the validation by Monte Carlo of methods for treating streaming in the calculation of diffusion coefficients. Comparisons are shown between the heterogeneity effects calculated by the Karlsruhe and Winfrith methods for typical pin and plate cells used in the BIZET experimental programme, and their effect in a whole reactor calculation is indicated. Comparisons are given with measurements which provide tests of the heterogeneity calculations. These include reaction rate scans within pin and plate cells, and reaction rate measurements across sectors of pin and plate fuel, where the flux tilt is determined by the relative reactivity of the pin and plate cells. Finally, the heterogeneity problems arising in the interpretation of reaction rate measurements are discussed. (author)

A computational analysis on homogeneous-heterogeneous mechanism in Carreau fluid flow

Science.gov (United States)

Khan, Imad; Rehman, Khalil Ur; Malik, M. Y.; Shafquatullah

2018-03-01

In this article magnetohydrodynamic Carreau fluid flow towards stretching cylinder is considered in the presence of homogeneous-heterogeneous reactions effect. The flow model is structured by utilizing theoretical grounds. For the numerical solution a shooting method along with Runge-Kutta algorithm is executed. The outcomes are provided through graphs. It is observed that the Carreau fluid concentration shows decline values via positive iterations of homogeneous-heterogeneous reaction parameters towards both shear thinning and thickening case. The present work is certified through comparison with already existing literature in a limiting sense.

Microwaves in chemistry: Another way of heating reaction mixtures

Science.gov (United States)

Berlan, J.

1995-04-01

The question of a possible "microwave activation" of chemical reaction is discussed. In fact two cases should be distinguished: homogeneous or heterogeneous reaction mixtures. In homogeneous mixtures there are no (or very low) rate enhancements compared to a conventional heating, but some influence on chemioselectivity has been observed. These effects derive from fast and mass heating of microwaves, and probably, especially under reflux, from different boiling rates and/or overheating. With heterogeneous mixtures non conventional effects probably derive from mass heating and selective overheating. This is illustrated with several reactions: Diels-Alder, naphthalene sulphonation, preparation of cyanuric acid, hydrolysis of nitriles, transposition reaction on solid support.

Evolving transpeptidase and hydrolytic variants of γ-glutamyl transpeptidase from Bacillus licheniformis by targeted mutations of conserved residue Arg109 and their biotechnological relevance.

Science.gov (United States)

Bindal, Shruti; Sharma, Sujata; Singh, Tej P; Gupta, Rani

2017-05-10

γ-Glutamyl transpeptidase (GGT) catalyzes the transfer of the γ-glutamyl moiety from donor compounds such as l-glutamine (Gln) and glutathione (GSH) to an acceptor. During the biosynthesis of various γ-glutamyl-containing compounds using GGT enzyme, auto-transpeptidation reaction leads to the formation of unwanted byproducts. Therefore, in order to alter the auto-transpeptidase activity of the GGT enzyme, the binding affinity of Gln should be modified. Structural studies of the Bacillus licheniformis GGT (BlGT) complexed with the glutamic acid has shown that glutamic acid has strong ionic interactions through its α-carboxlic group with the guanidine moiety of Arg109. This interaction appears to be an important contributor for the binding affinity of Gln. In view of this, six mutants of Bacillus licheniformis ER15 GGT (BlGGT) viz. Arg109Lys, Arg109Ser, Arg109Met, Arg109Leu, Arg109Glu and Arg109Phe were prepared. As seen from the structure of BlGT, the mutation of Arg109 to Lys109 may reduce the affinity for Gln to some extent, whereas the other mutations are expected to lower the affinity much more. Biophysical characterization and functional studies revealed that Arg109Lys mutant has increased transpeptidation activity and catalytic efficiency than the other mutants. The Arg109Lys mutant showed high conversion rates for l-theanine synthesis as well. Moreover, the Arg109Met mutant showed increased hydrolytic activity as it completely altered the binding of Gln at the active site. Also, the salt stability of the enzyme was significantly improved on replacing Arg109 by Met109 which is required for hydrolytic applications of GGTs in food industries. Copyright © 2017 Elsevier B.V. All rights reserved.

Identification of thermophilic bacterial strains producing thermotolerant hydrolytic enzymes from manure compost.

Science.gov (United States)

Charbonneau, David M; Meddeb-Mouelhi, Fatma; Boissinot, Maurice; Sirois, Marc; Beauregard, Marc

2012-03-01

Ten thermophilic bacterial strains were isolated from manure compost. Phylogenetic analysis based on 16S rRNA genes and biochemical characterization allowed identification of four different species belonging to four genera: Geobacillus thermodenitrificans, Bacillus smithii, Ureibacillus suwonensis and Aneurinibacillus thermoaerophilus. PCR-RFLP profiles of the 16S-ITS-23S rRNA region allowed us to distinguish two subgroups among the G. thermodenitrificans isolates. Isolates were screened for thermotolerant hydrolytic activities (60-65°C). Thermotolerant lipolytic activities were detected for G. thermodenitrificans, A. thermoaerophilus and B. smithii. Thermotolerant protease, α-amylase and xylanase activities were also observed in the G. thermodenitrificans group. These species represent a source of potential novel thermostable enzymes for industrial applications.

[Description of the phylogenetic structure of hydrolytic prokaryotic complex in the soils].

Science.gov (United States)

Lukacheva, E G; Chernov, T I; Bykova, E M; Vlasenko, A N; Manucharova, N A

2013-01-01

With the help of the molecular-biological method of cell hybridization in situ (FISH), the abundance of a physiologically active hydrolytic prokaryotic complex in chernozem and gley-podzolic soils is determined. The total proportion of metabolically active cells, which were detected by hybridization with universal probes as representatives of the domains Bacteria and Archaea, in samples of the studied soil, was from 38% for chernozem up to 78% for gley-podzolic soil of the total number of cells. The differences in the structure of chitinolytic and pectinolytic prokaryotic soil complexes are detected. Along with the high abundance of Actinobacteria and Firmicutes in the soils with chitin, an increase in phylogenetic groups such as Alphaproteobacteria and Bacteroidetes is observed.

Kinetic equation of heterogeneous catalytic isotope exchange

Energy Technology Data Exchange (ETDEWEB)

Trokhimets, A I [AN Belorusskoj SSR, Minsk. Inst. Fiziko-Organicheskoj Khimii

1979-12-01

A kinetic equation is derived for the bimolecular isotope exchange reaction between AXsub(n)sup(*) and BXsub(m)sup(o), all atoms of element X in each molecule being equivalent. The equation can be generalized for homogeneous and heterogeneous catalytic isotope exchange.

Palladium-catalyzed coupling reactions

CERN Document Server

Molnár, Árpád

2013-01-01

This handbook and ready reference brings together all significant issues of practical importance for interested readers in one single volume. While covering homogeneous and heterogeneous catalysis, the text is unique in focusing on such important aspects as using different reaction media, microwave techniques or catalyst recycling. It also provides a comprehensive treatment of modern-day coupling reactions and emphasizes those topics that show potential for future development, such as continuous flow systems, water as a reaction medium, and catalyst immobilization, among others. With i

Determination of ethamsylate in pharmaceutical preparations based on an auto-oxidation chemiluminescence reaction.

Science.gov (United States)

Yang, Fengzhen; Zhang, Chao; Baeyens, Willy R G; Zhang, Xinrong

2002-10-15

Strong chemiluminescence emission has been observed by mixing alkaline hydrolytic products of ethamsylate with Tween 80 in acidic rhodamine 6G solution. This phenomenon has been utilized to design a flow-injection chemiluminescence method for the determination of ethamsylate in a pharmaceutical preparation. Under the optimum conditions, the proposed procedure has a linear range between 0.05 and 2.0 microg ml(-1), with a detection limit of 0.02 microg ml(-1) for ethamsylate. The method was applied to the determination of ethamsylate in pharmaceutical preparations. The possible mechanism of this chemiluminescence reaction was proposed. Copyright 2002 Elsevier Science B.V.

Multiscale Investigation on Biofilm Distribution and Its Impact on Macroscopic Biogeochemical Reaction Rates

Science.gov (United States)

Yan, Zhifeng; Liu, Chongxuan; Liu, Yuanyuan; Bailey, Vanessa L.

2017-11-01

Biofilms are critical locations for biogeochemical reactions in the subsurface environment. The occurrence and distribution of biofilms at microscale as well as their impacts on macroscopic biogeochemical reaction rates are still poorly understood. This paper investigated the formation and distributions of biofilms in heterogeneous sediments using multiscale models and evaluated the effects of biofilm heterogeneity on local and macroscopic biogeochemical reaction rates. Sediment pore structures derived from X-ray computed tomography were used to simulate the microscale flow dynamics and biofilm distribution in the sediment column. The response of biofilm formation and distribution to the variations in hydraulic and chemical properties was first examined. One representative biofilm distribution was then utilized to evaluate its effects on macroscopic reaction rates using nitrate reduction as an example. The results revealed that microorganisms primarily grew on the surfaces of grains and aggregates near preferential flow paths where both electron donor and acceptor were readily accessible, leading to the heterogeneous distribution of biofilms in the sediments. The heterogeneous biofilm distribution decreased the macroscopic rate of biogeochemical reactions as compared with those in homogeneous cases. Operationally considering the heterogeneous biofilm distribution in macroscopic reactive transport models such as using dual porosity domain concept can significantly improve the prediction of biogeochemical reaction rates. Overall, this study provided important insights into the biofilm formation and distribution in soils and sediments as well as their impacts on the macroscopic manifestation of reaction rates.

Advances in heterogeneous autocatalytic reactions applied to uranium dissolution - 5317

International Nuclear Information System (INIS)

Marc, P.; Magnaldo, A.; Godard, J.; Schaer, E.

2015-01-01

Dissolution and the solubilization of the chemical elements is a milestone of the head-end of hydrometallurgical processes. When dissolving spent nuclear fuels, additional constraints are added due to the permanent need to strictly control and limit the hold-up. Thus the need for kinetic modeling concerning the dissolution of spent nuclear fuels in nitric acid. This study aims at better understanding the chemical and physical-chemical phenomena of uranium dioxide dissolution reactions in nitric medium. It has been documented that the nitric acid attack of sintering-manufactured uranium dioxide solids occurs through preferential attack sites. This non uniform attack leads to the development of cracks in the solids. Optical microscopy observations show that in some cases, the development of these cracks can lead to the solid cleavage. In this case, we show that the dissolution of the detached fragments is much slower than the time required for the complete cleavage of the solid. These points motivated the measurements of dissolution kinetics using optical microscopy and image processing. A comparison of the measured kinetics with the diffusion kinetics by the mean of the external resistance fraction allows discriminating between measured kinetics corresponding to the chemical reaction or mass-transport limitation. This capability to measure, for the very first time, the 'true' chemical kinetics of the reaction has enabled the confirmation of the highly autocatalytic nature of the reaction, and first evaluation of the constants of the chemical reactions kinetic laws. These data are fundamental to set the kinetic parameters of the chemical reactions in a future model of the dissolution of uranium dioxide sintered pellets. (authors)

Heterogeneous reaction of SO2 with soot: The roles of relative humidity and surface composition of soot in surface sulfate formation

Science.gov (United States)

Zhao, Yan; Liu, Yongchun; Ma, Jinzhu; Ma, Qingxin; He, Hong

2017-03-01

The conversion of SO2 to sulfates on the surface of soot is still poorly understood. Soot samples with different fractions of unsaturated hydrocarbons and oxygen-containing groups were prepared by combusting n-hexane under well-controlled conditions. The heterogeneous reaction of SO2 with soot was investigated using in situ attenuated total internal reflection infrared (ATR-IR) spectroscopy, ion chromatography (IC) and a flow tube reactor at the ambient pressure and relative humidity (RH). Water promoted SO2 adsorption and sulfate formation at the RH range from 6% to 70%, while exceeded water condensed on soot was unfavorable for sulfate formation due to inhibition of SO2 adsorption when RH was higher than 80%. The surface composition of soot, which was governed by combustion conditions, also played an important role in the heterogeneous reaction of SO2 with soot. This effect was found to greatly depend on RH. At low RH of 6%, soot with the highest fuel/oxygen ratio of 0.162 exhibited a maximum uptake capacity for SO2 because it contained a large amount of aromatic Csbnd H groups, which acted as active sites for SO2 adsorption. At RH of 54%, soot produced with a fuel/oxygen ratio of 0.134 showed the highest reactivity toward SO2 because it contained appropriate amounts of aromatic Csbnd H groups and oxygen-containing groups, subsequently leading to the optimal surface concentrations of both SO2 and water. These results suggest that variation in the surface composition of soot from different sources and/or resulting from chemical aging in the atmosphere likely affects the conversion of SO2 to sulfates.

Reaction Heterogeneity in LiNi _0.8 Co _0.15 Al _0.05 O ₂ Induced by Surface Layer

Energy Technology Data Exchange (ETDEWEB)

Grenier, Antonin [X-ray; Liu, Hao [X-ray; Wiaderek, Kamila M. [X-ray; Lebens-Higgins, Zachary W. [Department; Borkiewicz, Olaf J. [X-ray; Piper, Louis F. J. [Department; Chupas, Peter J. [Energy; Chapman, Karena W. [X-ray

2017-08-15

Through operando synchrotron powder X-ray diffraction (XRD) analysis of layered transition metal oxide electrodes of composition LiNi0.8Co0.15Al0.05O2 (NCA), we decouple the intrinsic bulk reaction mechanism from surface-induced effects. For identically prepared and cycled electrodes stored in different environments, we demonstrate that the intrinsic bulk reaction for pristine NCA follows solid-solution mechanism, not a two-phase as suggested previously. By combining high resolution powder X-ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and surface sensitive X-ray photoelectron spectroscopy (XPS), we demonstrate that adventitious Li2CO3 forms on the electrode particle surface during exposure to air, through reaction with atmospheric CO2. This surface impedes ionic and electronic transport to the underlying electrode, with progressive erosion of this layer during cycling giving rise to different reaction states in particles with an intact vs an eroded Li2CO3 surface-coating. This reaction heterogeneity, with a bimodal distribution of reaction states, has previously been interpreted as a “two-phase” reaction mechanism for NCA, as an activation step that only occurs during the first cycle. Similar surface layers may impact the reaction mechanism observed in other electrode materials using bulk probes such as operando powder XRD.

Rate tracer studies of heterogeneous catalysis

Energy Technology Data Exchange (ETDEWEB)

Happel, J; Kiang, S

1977-10-01

An analysis is presented of the extent to which parameters involved in transient tracing of isotopic species in heterogeneous catalysis can be determined by experiments in which tracer concentrations are measured as a function of time. Different treatments for open and closed systems with the over-all reaction at equilibrium or irreversible were developed.

Rapid and facile preparation of zinc ferrite (ZnFe{sub 2}O{sub 4}) oxide by microwave-solvothermal technique and its catalytic activity in heterogeneous photo-Fenton reaction

Energy Technology Data Exchange (ETDEWEB)

Anchieta, Chayene G.; Severo, Eric C.; Rigo, Caroline; Mazutti, Marcio A. [Department of Chemical Engineering, Federal University of Santa Maria, 97105-900, Santa Maria (Brazil); Kuhn, Raquel C., E-mail: raquelckuhn@yahoo.com.br [Department of Chemical Engineering, Federal University of Santa Maria, 97105-900, Santa Maria (Brazil); Muller, Edson I.; Flores, Erico M.M. [Department of Chemistry, Federal University of Santa Maria, 97105-900, Santa Maria (Brazil); Moreira, Regina F.P.M. [Department of Chemical Engineering and Food Engineering, Federal University of Santa Catarina, 88040-970, Florianópolis (Brazil); Foletto, Edson L. [Department of Chemical Engineering, Federal University of Santa Maria, 97105-900, Santa Maria (Brazil)

2015-06-15

In this work zinc ferrite (ZnFe{sub 2}O{sub 4}) oxide was rapidly and easily prepared by microwave-solvothermal route and its catalytic property in photo-Fenton reaction was evaluated. The effects of microwave heating time and power on the properties of produced particles were investigated. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and nitrogen adsorption–desorption isotherms were the techniques used for characterizing the solid products. The synthesized material was tested as a catalyst in the degradation of the textile dye molecule by the heterogeneous photo-Fenton process. Characterization results showed that the microwave heating time and power have significant influences on the formation of the phase spinel as well as on its physical properties. The reaction results showed that the ZnFe{sub 2}O{sub 4} oxide has good photocatalytic activity, which can be attributed to high surface area and pore volume, and large pore size. The ZnFe{sub 2}O{sub 4} oxide produced by the microwave irradiation exhibited promising photocatalytic activity for the removal of textile dye, reaching nearly 100% of decolorization at 40 min and 60% of mineralization at 240 min. Therefore, ZnFe{sub 2}O{sub 4} particles rapidly prepared by the microwave route have the potential for use in treatment of textile wastewater by the heterogeneous photo-Fenton process. - Highlights: • ZnFe{sub 2}O{sub 4} was synthesized by microwave-solvothermal method. • ZnFe{sub 2}O{sub 4} was prepared by different microwave heating times and powers. • ZnFe{sub 2}O{sub 4} was used as heterogeneous photo-Fenton catalyst. • Degradation of Procion red dye using heterogeneous photo-Fenton process. • ZnFe{sub 2}O{sub 4} was highly efficient to degrade textile dye under visible light.

Unfolded protein response is required for Aspergillus oryzae growth under conditions inducing secretory hydrolytic enzyme production.

Science.gov (United States)

Tanaka, Mizuki; Shintani, Takahiro; Gomi, Katsuya

2015-12-01

Unfolded protein response (UPR) is an intracellular signaling pathway for adaptation to endoplasmic reticulum (ER) stress. In yeast UPR, Ire1 cleaves the unconventional intron of HAC1 mRNA, and the functional Hac1 protein translated from the spliced HAC1 mRNA induces the expression of ER chaperone genes and ER-associated degradation genes for the refolding or degradation of unfolded proteins. In this study, we constructed an ireA (IRE1 ortholog) conditionally expressing strain of Aspergillus oryzae, a filamentous fungus producing a large amount of amylolytic enzymes, and examined the contribution of UPR to ER stress adaptation under physiological conditions. Repression of ireA completely blocked A. oryzae growth under conditions inducing the production of hydrolytic enzymes, such as amylases and proteases. This growth defect was restored by the introduction of unconventional intronless hacA (hacA-i). Furthermore, UPR was observed to be induced by amylolytic gene expression, and the disruption of the transcriptional activator for amylolytic genes resulted in partial growth restoration of the ireA-repressing strain. In addition, a homokaryotic ireA disruption mutant was successfully generated using the strain harboring hacA-i as a parental host. These results indicated that UPR is required for A. oryzae growth to alleviate ER stress induced by excessive production of hydrolytic enzymes. Copyright © 2015 Elsevier Inc. All rights reserved.

Determining two-step control in heterogeneous catalytic reactions

Energy Technology Data Exchange (ETDEWEB)

Chakrabarty, T; Silveston, P L; Hudgins, R R

1979-10-01

The data by Thaller and Thodos on the sec.-butanol dehydrogenation to methyl ethyl ketone on brass catalyst indicated that a dual site surface reaction was rate-controlling below 575/sup 0/K and hydrogen desorption was rate-controlling above 616/sup 0/K (Vertical BarAIChE J.

Pore-scale studies of multiphase flow and reaction involving CO2 sequestration in geologic formations

Science.gov (United States)

Kang, Q.; Wang, M.; Lichtner, P. C.

2008-12-01

In geologic CO2 sequestration, pore-scale interfacial phenomena ultimately govern the key processes of fluid mobility, chemical transport, adsorption, and reaction. However, spatial heterogeneity at the pore scale cannot be resolved at the continuum scale, where averaging occurs over length scales much larger than typical pore sizes. Natural porous media, such as sedimentary rocks and other geological media encountered in subsurface formations, are inherently heterogeneous. This pore-scale heterogeneity can produce variabilities in flow, transport, and reaction processes that take place within a porous medium, and can result in spatial variations in fluid velocity, aqueous concentrations, and reaction rates. Consequently, the unresolved spatial heterogeneity at the pore scale may be important for reactive transport modeling at the larger scale. In addition, current continuum models of surface complexation reactions ignore a fundamental property of physical systems, namely conservation of charge. Therefore, to better understand multiphase flow and reaction involving CO2 sequestration in geologic formations, it is necessary to quantitatively investigate the influence of the pore-scale heterogeneity on the emergent behavior at the field scale. We have applied the lattice Boltzmann method to simulating the injection of CO2 saturated brine or supercritical CO2 into geological formations at the pore scale. Multiple pore-scale processes, including advection, diffusion, homogeneous reactions among multiple aqueous species, heterogeneous reactions between the aqueous solution and minerals, ion exchange and surface complexation, as well as changes in solid and pore geometry are all taken into account. The rich pore scale information will provide a basis for upscaling to the continuum scale.

Mechanical properties, morphology, and hydrolytic degradation behavior of polylactic acid / natural rubber blends

Science.gov (United States)

Buys, Y. F.; Aznan, A. N. A.; Anuar, H.

2018-01-01

Due to its biodegradability and renewability, polylactic acid (PLA) has been receiving enormous attention as a potential candidate to replace petroleum based polymers. However, PLA has limitation due to its inherent brittleness. In order to overcome this limitation, blending PLA with elastomeric materials such as natural rubber (NR) are commonly reported. In previous, several researches on PLA/NR blend had been reported, with most of them evaluated the mechanical properties. On the other hand, study of degradation behavior is significance of importance, as controlling materials degradation is required in some applications. This research studied the effect of blend composition on mechanical properties, morphology development, and hydrolytic degradation behavior of PLA/NR blends. Various compositions of PLA/NR blends were prepared by melt blending technique. Tensile test and impact test of the blends were performed to evaluate the mechanical properties. Addition of NR improved the elongation at break and impact strength of the blends, but reduced the tensile strength and stiffness of the specimens. Dynamic Mechanical Analysis (DMA) measurements of the blends displayed two peaks at temperature -70˚C which corresponded to T g of NR and 65˚C which corresponded to T g of PLA. Field Emission Scanning Electron Microscopy (FE-SEM) micrograph of 70/30 PLA/NR specimen also showed two distinct phases, which lead to indication that PLA/NR blends are immiscible. Hydrolytic degradation behavior was evaluated by measuring the remaining weight of the samples immersed in sodium hydroxide solution for a predetermined times. It was shown that the degradation behavior of PLA/NR blends is affected by composition of the blends, with 100 PLA and 70/30 PLA/NR blend showed the fastest degradation rate and 100 NR displayed the slowest one.

Fe–Co/sulfonated polystyrene as an efficient and selective catalyst in heterogeneous Baeyer–Villiger oxidation reaction of cyclic ketones

Directory of Open Access Journals (Sweden)

Yingting Wang

2018-02-01

Full Text Available A highly efficient catalyst Fe–Co/sulfonated polystyrene (Fe–Co/SPS was introduced and synthesized, which catalyzed BV oxidation of ketones with aqueous hydrogen peroxide to give the corresponding lactones in high yield and selectivity. Solid acid catalyst of Fe–Co/SPS has been prepared by using the 98-wt% sulfuric acid as the sulfonating agent and CoCl2 combined FeCl3 as sources of metal ions. Various physical–chemical characterizations including FT-IR, XRD, SEM and TGA, revealed that bimetallic ions Fe3+–Co2+ species in the sulfonated polystyrene framework were responsible for the catalytic activities. The BV reaction catalyzed by Fe–Co/SPS highlighted the special effects between metal ions and protonic acids as well as solvent-free heterogeneous catalytic oxidation with excellent conversion.

THE COORDINATION COMPOUNDS OF COBALT (II, III) WITH DITHIOCARBAMIC ACID DERIVATIVES — MODIFICATORS OF HYDROLYTIC ENZYMES ACTIVITY

OpenAIRE

L. D. Varbanets; О. V. Matselyukh; N. А. Nidyalkova; Е. V. Аvdiyuk; А. V. Gudzenko; I. I. Seifullina; G. N. Маsаnоvets; N. V. Khitrich

2013-01-01

Chloride, bromide and isothiocyanate complexes of cobalt(II) with N-substituted thiocarbamoyl-N?-pentamethylenesulfenamides (1)–(12), and also complexes of cobalt(II, Ш) with derivatives of morpholine-4-carbodithioic acid (13)–(18) have been used as modificators of enzymes of hydrolytic action — Bacillus thurin-giensis ІМВ В-7324 peptidases, Bacillus subtilis 147 and Aspergillus flavus var. oryzae 80428 amylases, Eupenicillium erubescens 248 and Cryptococcus albidus 1001 rhamnosidases. It was...

EFFECTS OF PORE STRUCTURE CHANGE AND MULTI-SCALE HETEROGENEITY ON CONTAMINANT TRANSPORT AND REACTION RATE UPSCALING

Energy Technology Data Exchange (ETDEWEB)

Lindquist, W. Brent; Jones, Keith W.; Um, Wooyong; Rockhold, mark; Peters, Catherine A.; Celia, Michael A.

2013-02-15

secondary mineral precipitates (cancrinite), conducting experiments under conditions with and without Al allowed us to experimentally separate the conditions that lead to quartz dissolution from the conditions that lead to quartz dissolution plus cancrinite precipitation. Consistent with our expectations, in the experiments without Al, there was a substantial reduction in volume of the solid matrix. With Al there was a net increase in the volume of the solid matrix. The rate and extent of reaction was found to increase with temperature. These results demonstrate a successful effort to identify conditions that lead to increases and conditions that lead to decreases in solid matrix volume due to reactions of caustic tank wastes with quartz sands. In addition, we have begun to work with slightly larger, intermediate-scale columns packed with Hanford natural sediments and quartz. Similar dissolution and precipitation were observed in these colums. The measurements are being interpreted with reactive transport modeling using STOMP; preliminary observations are reported here. 2) Multi-Scale Imaging and Analysis. Mineral dissolution and precipitation rates within a porous medium will be different in different pores due to natural heterogeneity and the heterogeneity that is created from the reactions themselves. We used a combination of X-ray computed microtomography, backscattered electron and energy dispersive X-ray spectroscopy combined with computational image analysis to quantify pore structure, mineral distribution, structure changes and fluid-air and fluid-grain interfaces. Results and Key Findings: Three of the columns from the reactive flow experiments at PNNL (S1, S3, S4) were imaged using 3D X-ray computed microtomography (XCMT) at BNL and analyzed using 3DMA-rock at SUNY Stony Brook. The imaging results support the mass balance findings reported by Dr. Um’s group, regarding the substantial dissolution of quartz in column S1. An important observation is that of grain

Noninvasive In-Vivo Quantification of Mechanical Heterogeneity of Invasive Breast Carcinomas.

Directory of Open Access Journals (Sweden)

Tengxiao Liu

Full Text Available Heterogeneity is a hallmark of cancer whether one considers the genotype of cancerous cells, the composition of their microenvironment, the distribution of blood and lymphatic microvasculature, or the spatial distribution of the desmoplastic reaction. It is logical to expect that this heterogeneity in tumor microenvironment will lead to spatial heterogeneity in its mechanical properties. In this study we seek to quantify the mechanical heterogeneity within malignant and benign tumors using ultrasound based elasticity imaging. By creating in-vivo elastic modulus images for ten human subjects with breast tumors, we show that Young's modulus distribution in cancerous breast tumors is more heterogeneous when compared with tumors that are not malignant, and that this signature may be used to distinguish malignant breast tumors. Our results complement the view of cancer as a heterogeneous disease on multiple length scales by demonstrating that mechanical properties within cancerous tumors are also spatially heterogeneous.

Hydrolytic and radiolytic degradation of TBP in TBP.30% V/V-dodecane/UO2(NO3)2.HNO3.H2O systems

International Nuclear Information System (INIS)

Barreta, L.G.

1980-01-01

The hydrolytic and radiolytic degradation of TBP is investigated in systems of TBP 30% V/V-dodecane/H 2 O . HNO 3 . UO 2 (NO 3 ) 2 by gas chromatographic determination of HDBP. No direct relation between the concentration of HDBP formed and the quantity of HNO 3 extracted by the organic phase is observed in the studies of hydrolysis of TBP. The HDBP concentration is seen to increase non-linearly with the concentration of HNO 3 extracted by the organic phase. Radiolytic studies show that for doses greater than 1 Wh/l, the concentration of HDBP formed increases with the dose absorbed by the system. Whith doses smaller than 1 Wh/l and acid concentration greater than 2 M, two distinct patterns of behavior are observed. The concentration of HDBP as a function of the radiation dose absorbed by the system presents a minimum for uranyl nitrate concentrations smaller than 0.9 M; for uranyl nitrate concentrations greater than 1.3 M the concentration of radiolytic HDBP cannot be calculated because the concentration of the hydrolytic HDBP determined is greater than the sum of the experimental concentrations of hydrolytic and radiolytic HDBP. It is known that the dose absorbed by the process solutions during the reprocessing of light water reactor fuel elements is smaller than one Wh/l. Thus, dose rates between zero and one Wh/l should be studied for this system. (Author) [pt

Surface science and heterogeneous catalysis

International Nuclear Information System (INIS)

Somorjai, G.A.

1980-05-01

The catalytic reactions studied include hydrocarbon conversion over platinum, the transition metal-catalyzed hydrogenation of carbon monoxide, and the photocatalyzed dissociation of water over oxide surfaces. The method of combined surface science and catalytic studies is similar to those used in synthetic organic chemistry. The single-crystal models for the working catalyst are compared with real catalysts by comparing the rates of cyclopropane ring opening on platinum and the hydrogenation of carbon monoxide on rhodium single crystal surface with those on practical commercial catalyst systems. Excellent agreement was obtained for these reactions. This document reviews what was learned about heterogeneous catalysis from these surface science approaches over the past 15 years and present models of the active catalyst surface

Heterogeneous reduction of nitric oxide on synthetic coal chars

Energy Technology Data Exchange (ETDEWEB)

C. Pevida; A. Arenillas; F. Rubiera; J.J. Pis [Instituto Nacional del Carbon (CSIC), Oviedo (Spain)

2005-12-01

Model compounds, with a controlled heteroatoms content and well-defined functionalities, were used to study the release of nitrogen compounds from char combustion. In the present work, the mechanisms involved in NO-char heterogeneous reduction were studied with a synthetic coal (SC) char as carbon source. Another synthetic char (SN) without any nitrogen in its composition was also employed in these studies. Temperature programmed reduction (TPR) tests with a gas mixture of 400 ppm NO in argon and with isotopically labelled nitric oxide, {sup 15}NO (500 ppm {sup 15}NO in argon), were carried out. The gases produced were quantitatively determined by means of MS and FTIR analysers. Under the conditions of this work the main products of the NO-C reaction were found to be N{sub 2} and CO{sub 2}. The main path of reaction involves the formation of surface nitrogen compounds that afterwards react with nitrogen from the reactive gas to form N{sub 2}. It was observed that fuel-N also participates in the overall heterogeneous reduction reaction, although to a lesser extent.

Novel Materials through Non-Hydrolytic Sol-Gel Processing: Negative Thermal Expansion Oxides and Beyond

Directory of Open Access Journals (Sweden)

Cora Lind

2010-04-01

Full Text Available Low temperature methods have been applied to the synthesis of many advanced materials. Non-hydrolytic sol-gel (NHSG processes offer an elegant route to stable and metastable phases at low temperatures. Excellent atomic level homogeneity gives access to polymorphs that are difficult or impossible to obtain by other methods. The NHSG approach is most commonly applied to the preparation of metal oxides, but can be easily extended to metal sulfides. Exploration of experimental variables allows control over product stoichiometry and crystal structure. This paper reviews the application of NHSG chemistry to the synthesis of negative thermal expansion oxides and selected metal sulfides.

Scale-up of heterogeneous catalytic reactions

Energy Technology Data Exchange (ETDEWEB)

Heggs, P; Sunderland, P

1979-12-01

This report on the Institution of Chemical Engineers ''Problems in Applied Catalysis'' Meeting (Bath, U.K. 1/4-5/78) covers papers on the nature of the catalyst surface, including the use of IR spectroscopy, electron energy loss spectroscopy, low-energy electron diffraction, electron spectroscopy, secondary ion mass spectroscopy, and modular-beam scattering for investigating solid surfaces and their relevance to catalysis; study of the reaction mechanisms by which catalysis takes place; use of mechanistic models to determine the true chemical kinetics illustrated for the oxidation of benzene to maleic anhydride over a vanadium pentoxide/molybdenum trioxide catalyst; the study with respect to the importance of transport effects in catalyst pellets on scale-up, falsification of true kinetics, and the design of laboratory reactors; full-scale reactor design of packed-bed reactors; and practical scale-up problems illustrated for methanol synthesis over a copper catalyst, ammonia oxidation over a cobalt oxide catalyst, and the steam reforming of naphtha.

Silica sulfuric acid: a versatile and reusable heterogeneous catalyst ...

African Journals Online (AJOL)

... and reusable heterogeneous catalyst for the synthesis of N-acyl carbamates and ... All the reactions were done at room temperature and the N-acyl carbamates ... This method is attractive and is in a close agreement with green chemistry.

The influence of the length of the degradable segment on the functional properties and hydrolytic stability of multi-component polyurethane elastomeric films

Czech Academy of Sciences Publication Activity Database

Špírková, Milena; Hodan, Jiří; Kobera, Libor; Kredatusová, Jana; Kubies, Dana; Machová, Luďka; Poreba, Rafal; Serkis, Magdalena; Zhigunov, Alexander; Kotek, Jiří

2017-01-01

Roč. 137, March (2017), s. 216-228 ISSN 0141-3910 R&D Projects: GA ČR(CZ) GA13-06700S Institutional support: RVO:61389013 Keywords : polyurethane elastomer * lactide * hydrolytic degradation Subject RIV: CD - Macromolecular Chemistry OBOR OECD: Polymer science Impact factor: 3.386, year: 2016

Investigation on ultrasonication mediated biosurfactant disintegration method in sludge flocs for enhancing hydrolytic enzymes activity and polyhydroxyalkanoates.

Science.gov (United States)

Sethupathy, A; Sivashanmugam, P

2018-06-04

In this study, a novel biosurfactant potential bacterial strain Pseudomonas pachastrellae RW43 was isolated from pulp and paper sludge and the biosurfactant namely rhamnolipid produced by Pseudomonas pachastrellae RW43 was investigated by varying pH and incubation time in batch liquid fermentation process. The maximal yield of rhamnolipid was found to be 12.1 g/L at an optimized condition of pH 7 and incubation time of 168 h. NMR analysis was performed for identification of molecular structure of produced rhamnolipid and its results concluded that the product was identified as di rhamnolipid. Then, statistically the global optimum conditions for hydrolytic enzymes extraction parameters (sonication power (100 W), extraction time (15 min) and rhamnolipid dosage (2% v/v)) were established. At 30,456 kJ/kg TS specific energy, ultrasonication with rhamnolipid disintegration method extracted maximal consortium activity of hydrolytic enzymes from mixed sludge (municipal and pulp & paper sludge) and the maximum observed were found to be 42.22, 51.75, 34.26, 24.21, 11.35 Units/g VSS respectively for protease, α-amylase, cellulase, lipase and α-glucosidase. Polyhydroxyalkanoates was recovered from enzymes extracted sludge using various solvents namely chloroform, sodium hypochlorite with chloroform and sodium lauryl sulfate with sodium hypochlorite. The maximum recovery was found to be 74 g/kg using sodium hypochlorite and chloroform extraction solvents.

Nitric oxide reduction in coal combustion: role of char surface complexes in heterogeneous reactions

Energy Technology Data Exchange (ETDEWEB)

Arenillas, A.; Rubiera, F.; Pis, J.J. [Instituto Nacional del Carbon, CSIC, Oviedo (Spain)

2002-12-15

Nitrogen oxides are one of the major environmental problems arising from fossil fuel combustion. Coal char is relatively rich in nitrogen, and so this is an important source of nitrogen oxides during coal combustion. However, due to its carbonaceous nature, char can also reduce NO through heterogeneous reduction. The objectives of this work were on one hand to compare NO emissions from coal combustion in two different types of equipment and on the other hand to study the influence of char surface chemistry on NO reduction. A series of combustion tests were carried out in two different scale devices: a thermogravimetric analyzer coupled to a mass spectrometer and an FTIR (TG-MS-FTIR) and a fluidized bed reactor with on-line battery of analyzers. According to the results obtained, it can be said that the TG-MS-FTIR system provides valuable information about NO heterogeneous reduction and it can give good trends of the behaviour in other combustion equipments, i.e. fluidized bed combustors. It has been also pointed out that NO-char interaction depends to a large extent on temperature. In the low-temperature range NO heterogeneous reduction seems to be controlled by the evolution of surface complexes. In the high-temperature range a different mechanism is involved in NO heterogeneous reduction, the nature of the carbon matrix being a key factor. 27 refs., 6 figs., 1 tab.

Heterogeneous catalysis: on bathroom mirrors and boiling stones

NARCIS (Netherlands)

Philipse, A.P.

2011-01-01

A catalyst is defined as a substance that accelerates a process without undergoing a net change due to that process. Most chemistry students learn about catalysts in the context of chemical reactions, such as the enzymes in biochemistry or the heterogeneous metal catalysts in inorganic chemistry (1,

Metagenomics as a Tool for Enzyme Discovery: Hydrolytic Enzymes from Marine-Related Metagenomes.

Science.gov (United States)

Popovic, Ana; Tchigvintsev, Anatoly; Tran, Hai; Chernikova, Tatyana N; Golyshina, Olga V; Yakimov, Michail M; Golyshin, Peter N; Yakunin, Alexander F

2015-01-01

This chapter discusses metagenomics and its application for enzyme discovery, with a focus on hydrolytic enzymes from marine metagenomic libraries. With less than one percent of culturable microorganisms in the environment, metagenomics, or the collective study of community genetics, has opened up a rich pool of uncharacterized metabolic pathways, enzymes, and adaptations. This great untapped pool of genes provides the particularly exciting potential to mine for new biochemical activities or novel enzymes with activities tailored to peculiar sets of environmental conditions. Metagenomes also represent a huge reservoir of novel enzymes for applications in biocatalysis, biofuels, and bioremediation. Here we present the results of enzyme discovery for four enzyme activities, of particular industrial or environmental interest, including esterase/lipase, glycosyl hydrolase, protease and dehalogenase.

Hydrolytic study of the copolymer Poly pyrrole/ Polyethyleneglycol and Poly pyrrole synthesized by plasma; Estudio hidrolitico del copolimero polipirrol/polietilenglicol y polipirrol sintetizado por plasma

Energy Technology Data Exchange (ETDEWEB)

Colin, E.; Enriquez, M.A.; Olayo, M.G.; Cruz, G.J.; Carapia, L.; Romero, M. [ININ, 52045 Ocoyoacac, Estado de Mexico (Mexico); Morales, J.; Olayo, R. [UAM-I, A.P. 55-534 Iztapalapa, Mexico D.F. (Mexico)

2006-07-01

In this work the study about the hydrolytic compatibility of semiconductor polymers, copolymer Poly pyrrole/ Polyethyleneglycol (PPy/PEG) and Poly pyrrole (PPy) for their possible use as biomaterials. The polymers were synthesized by plasma between 10 and 100 W, with discharges of splendor RF to 13.5 MHz with resistive coupling. The hydrolytic affinity was evaluated calculating the contact angle with solutions of NaCl, NaCl-MgSO{sub 4} and Krebs-Ringer. The results show a hydrophilicity increment due to the increase of the surface ruggedness with the synthesis energy. On the contrary, the crystallinity diminishes when increasing the power in PPy and it stays approximately constant in PPy/PEG. The electric conductivity presents a growth from 2 to 4 magnitude orders in function of the water content in the polymers. (Author)

Variation in pH optima of hydrolytic enzyme activities in tropical rain forest soils.

Science.gov (United States)

Turner, Benjamin L

2010-10-01

Extracellular enzymes synthesized by soil microbes play a central role in the biogeochemical cycling of nutrients in the environment. The pH optima of eight hydrolytic enzymes involved in the cycles of carbon, nitrogen, phosphorus, and sulfur, were assessed in a series of tropical forest soils of contrasting pH values from the Republic of Panama. Assays were conducted using 4-methylumbelliferone-linked fluorogenic substrates in modified universal buffer. Optimum pH values differed markedly among enzymes and soils. Enzymes were grouped into three classes based on their pH optima: (i) enzymes with acidic pH optima that were consistent among soils (cellobiohydrolase, β-xylanase, and arylsulfatase), (ii) enzymes with acidic pH optima that varied systematically with soil pH, with the most acidic pH optima in the most acidic soils (α-glucosidase, β-glucosidase, and N-acetyl-β-glucosaminidase), and (iii) enzymes with an optimum pH in either the acid range or the alkaline range depending on soil pH (phosphomonoesterase and phosphodiesterase). The optimum pH values of phosphomonoesterase were consistent among soils, being 4 to 5 for acid phosphomonoesterase and 10 to 11 for alkaline phosphomonoesterase. In contrast, the optimum pH for phosphodiesterase activity varied systematically with soil pH, with the most acidic pH optima (3.0) in the most acidic soils and the most alkaline pH optima (pH 10) in near-neutral soils. Arylsulfatase activity had a very acidic optimum pH in all soils (pH ≤3.0) irrespective of soil pH. The differences in pH optima may be linked to the origins of the enzymes and/or the degree of stabilization on solid surfaces. The results have important implications for the interpretation of hydrolytic enzyme assays using fluorogenic substrates.

Activities of Heterogeneous Acid-Base Catalysts for Fragrances Synthesis: A Review

Directory of Open Access Journals (Sweden)

Hartati Hartati

2013-06-01

Full Text Available This paper reviews various types of heterogeneous acid-base catalysts for fragrances preparation. Catalytic activities of various types of heterogeneous acid and base catalysts in fragrances preparation, i.e. non-zeolitic, zeolitic, and mesoporous molecular sieves have been reported. Generally, heterogeneous acid catalysts are commonly used in fragrance synthesis as compared to heterogeneous base catalysts. Heteropoly acids and hydrotalcites type catalysts are widely used as heterogeneous acid and base catalysts, respectively. © 2013 BCREC UNDIP. All rights reservedReceived: 20th January 2013; Revised: 31st March 2013; Accepted: 1st April 2013[How to Cite: Hartati, H., Santoso, M., Triwahyono, S., Prasetyoko, D. (2013. Activities of Heterogeneous Acid-Base Catalysts for Fragrances Synthesis: A Review. Bulletin of Chemical Reaction Engineering & Catalysis, 8 (1: 14-33. (doi:10.9767/bcrec.8.1.4394.14-33][Permalink/DOI: http://dx.doi.org/10.9767/bcrec.8.1.4394.14-33] | View in  |

Effects of network dissolution changes on pore-to-core upscaled reaction rates for kaolinite and anorthite reactions under acidic conditions

KAUST Repository

Kim, Daesang

2013-11-01

We have extended reactive flow simulation in pore-network models to include geometric changes in the medium from dissolution effects. These effects include changes in pore volume and reactive surface area, as well as topological changes that open new connections. The computed changes were based upon a mineral map from an X-ray computed tomography image of a sandstone core. We studied the effect of these changes on upscaled (pore-scale to core-scale) reaction rates and compared against the predictions of a continuum model. Specifically, we modeled anorthite and kaolinite reactions under acidic flow conditions during which the anorthite reactions remain far from equilibrium (dissolution only), while the kaolinite reactions can be near-equilibrium. Under dissolution changes, core-scale reaction rates continuously and nonlinearly evolved in time. At higher injection rates, agreement with predictions of the continuum model degraded significantly. For the far-from-equilibrium reaction, our results indicate that the ability to correctly capture the heterogeneity in dissolution changes in the reactive mineral surface area is critical to accurately predict upscaled reaction rates. For the near-equilibrium reaction, the ability to correctly capture the heterogeneity in the saturation state remains critical. Inclusion of a Nernst-Planck term to ensure neutral ionic currents under differential diffusion resulted in at most a 9% correction in upscaled rates.

Solid phase microextraction as a reliable alternative to conventional extraction techniques to evaluate the pattern of hydrolytically released components in Vitis vinifera L. grapes.

Science.gov (United States)

Perestrelo, Rosa; Caldeira, Michael; Câmara, José S

2012-06-15

In present research, headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-mass spectrometry (GC-qMS), was evaluated as a reliable and improved alternative to the commonly used liquid-liquid extraction (LLE) technique for the establishment of the pattern of hydrolytically released components of 7 Vitis vinifera L. grape varieties, commonly used to produce the world-famous Madeira wine. Since there is no data available on their glycosidic fractions, at a first step, two hydrolyse procedures, acid and enzymatic, were carried out using Boal grapes as matrix. Several parameters susceptible of influencing the hydrolytic process were studied. The best results, expressed as GC peak area, number of identified components and reproducibility, were obtained using ProZym M with b-glucosidase activity at 35°C for 42h. For the extraction of hydrolytically released components, HS-SPME technique was evaluated as a reliable and improved alternative to the conventional extraction technique, LLE (ethyl acetate). HS-SPME using DVB/CAR/PDMS as coating fiber displayed an extraction capacity two fold higher than LLE (ethyl acetate). The hydrolyzed fraction was mainly characterized by the occurrence of aliphatic and aromatic alcohols, followed by acids, esters, carbonyl compounds, terpenoids, and volatile phenols. Concerning to terpenoids its contribution to the total hydrolyzed fraction is highest for Malvasia Cândida (23%) and Malvasia Roxa (13%), and their presence according previous studies, even at low concentration, is important from a sensorial point of view (can impart floral notes to the wines), due to their low odor threshold (μg/L). According to the obtained data by principal component analysis (PCA), the sensorial properties of Madeira wines produced by Malvasia Cândida and Malvasia Roxa could be improved by hydrolysis procedure, since their hydrolyzed fraction is mainly characterized by terpenoids (e.g. linalool, geraniol) which are responsible

Supported ionic liquids: versatile reaction and separation media

DEFF Research Database (Denmark)

Riisager, Anders; Fehrmann, Rasmus; Haumann, Marco

2006-01-01

The latest developments in supported ionic liquid phase (SILP) systems for catalysis and separation technology are surveyed. The SILP concept combines the advantages of homogeneous catalysis with heterogeneous process technology, and a variety of reactions have been studied where supported ionic ...... liquid catalysts proved to be more active and selective than common systems. In separation applications the use of supported ionic liquids can facilitate selective transport of substrates across membranes.......The latest developments in supported ionic liquid phase (SILP) systems for catalysis and separation technology are surveyed. The SILP concept combines the advantages of homogeneous catalysis with heterogeneous process technology, and a variety of reactions have been studied where supported ionic...

Solubilization of low-rank coal by Trichoderma atroviride: Evidence for the involvement of hydrolytic and oxidative enzymes by using C-14-labelled lignite

Energy Technology Data Exchange (ETDEWEB)

Holker, U.; Schmiers, H.; Grosse, S.; Winkelhofer, M.; Polsakiewicz, M.; Ludwig, S.; Dohse, J.; Hofer, M. [University of Bonn, Bonn (Germany). Inst. of Botany

2002-04-01

The deuteromycete Trichoderma atroviride is able to solubilize lignite in dependence on a given carbon source for growth. When cultivated on media containing glutamate, this mold excreted a set of different enzymes with hydrolytic activity. Addition of lignite to the growth media induced the synthesis of extracellular lignite-specific esterase activity but no evidence has been provided for its direct involvement in the process of lignite solubilization. Hence, the basic capability of T. atroviride enzymes to degrade a variety of ester and ether bonds at the surface or within the bulky lignite structure was tested using coal following its direct labelling with C-14-alkyl iodide. The participation of hydrolytic and oxidative enzymes in lignite degradation was assessed by measuring the release of C-14 radioactivity from selectively alkylated carboxylic and phenolic OH groups. T. atroviride cleaved both carboxylic esters using esterases and the phenolic ether bonds by using oxidative enzymes, most likely laccases.

Carbene Transfer Reactions Catalysed by Dyes of the Metalloporphyrin Group

Directory of Open Access Journals (Sweden)

Mário M. Q. Simões

2018-03-01

Full Text Available Carbene transfer reactions are very important transformations in organic synthesis, allowing the generation of structurally challenging products by catalysed cyclopropanation, cyclopropenation, carbene C-H, N-H, O-H, S-H, and Si-H insertion, and olefination of carbonyl compounds. In particular, chiral and achiral metalloporphyrins have been successfully explored as biomimetic catalysts for these carbene transfer reactions under both homogeneous and heterogeneous conditions. In this work the use of synthetic metalloporphyrins (MPorph, M = Fe, Ru, Os, Co, Rh, Ir, Sn as homogeneous or heterogeneous catalysts for carbene transfer reactions in the last years is reviewed, almost exclusively focused on the literature since the year 2010, except when reference to older publications was deemed to be crucial.

Synthesis and photoluminescent properties of yttrium vanadate phosphor prepared by the non-hydrolytic sol–gel process

International Nuclear Information System (INIS)

Matos, Marcela G.; Faria, Emerson H. de; Rocha, Lucas A.; Calefi, Paulo S.; Ciuffi, Katia J.; Nassar, Eduardo J.; Sarmento, Victor Hugo Vitorino

2014-01-01

We used the non-hydrolytic sol–gel route to synthesize YVO 4 crystalline phases doped with europium III ion. We heat-treated the samples at 600, 800, and 1000 °C and characterized the materials by thermal analysis, X-ray diffraction, small-angle X-ray scattering, and photoluminescence. Larger weight loss occurred until 500 °C, ascribed to removal of residual precursor molecules. X-ray diffraction patterns evidenced YVO 4 phase formation at 600 °C. The crystallite size depended on the heat treatment temperature. SAXS showed that the nature of the system interfaces changed as a function of the thermal treatment. The excitation spectra of the samples displayed the charge transfer band. The photoluminescence data revealed the characteristic transition bands arising from the 5 D 0 → 5 F J (J=0, 1, 2, 3, and 4) manifolds under maximum excitation at the charge transfer band and the 5 L 6 level of the Eu 3+ ion. The 5 D 0 → 7 F 2 transition dominated the emission spectra, indicating that the Eu 3+ ion occupies a site without inversion center. The lifetime and quantum efficiency values were about 0.70 ms and 50%, respectively, corroborating literature results. -- Highlights: • This study described the preparation of the yttrium vanadate by non-hydrolytic sol–gel. • The SAXS curves can be interpreted from the fractal theory for a two-phase model. • The goal of the work is the preparation of the phosphors at low temperature. • The lifetimes depend on wavelength of the excitation

Advanced Heterogeneous Fenton Treatment of Coalbed Methane-Produced Water Containing Fracturing Fluid

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Meng Zhang

2018-04-01

Full Text Available This study investigated the heterogeneous Fenton treatment to process coalbed methane-produced water containing fracturing fluid and chose the development region of coalbed methane in the Southern Qinshui Basin as a research area. We synthesized the catalyst of Fe-Co/γ-Al2O3 by homogeneous precipitation method and characterized it by BET, XRD, SEM-EDS, FTIR, and XPS. Based on the degradation rate, we studied the influences of the heterogeneous Fenton method on the coalbed methane output water treatment process parameters, including initial pH, H2O2 concentration, and the catalyst concentration. We also investigated the impacts of overall reaction kinetics of heterogeneous catalytic oxidation on coalbed methane-produced water containing fracturing fluid. Results showed that Fe-Co/γ-Al2O3 as a Fenton catalyst has a good catalytic oxidation effect and can effectively process coalbed methane-produced water. This reaction also followed first-order kinetics. The optimal conditions were as follows: the initial pH of 3.5, a H2O2 concentration of 40 mol L−1, a catalyst concentration of 4 g/L, and an apparent reaction rate constant of 0.0172 min−1. Our results provided a basis to establish methods for treating coalbed methane-produced water.

N-Alkylation by Hydrogen Autotransfer Reactions.

Science.gov (United States)

Ma, Xiantao; Su, Chenliang; Xu, Qing

2016-06-01

Owing to the importance of amine/amide derivatives in all fields of chemistry, and also the green and environmentally benign features of using alcohols as alkylating reagents, the relatively high atom economic dehydrative N-alkylation reactions of amines/amides with alcohols through hydrogen autotransfer processes have received much attention and have developed rapidly in recent decades. Various efficient homogeneous and heterogeneous transition metal catalysts, nano materials, electrochemical methods, biomimetic methods, asymmetric N-alkylation reactions, aerobic oxidative methods, and even certain transition metal-free, catalyst-free, or autocatalyzed methods, have also been developed in recent years. With a brief introduction to the background and developments in this area of research, this chapter focuses mainly on recent progress and technical and conceptual advances contributing to the development of this research in the last decade. In addition to mainstream research on homogeneous and heterogeneous transition metal-catalyzed reactions, possible mechanistic routes for hydrogen transfer and alcohol activation, which are key processes in N-alkylation reactions but seldom discussed in the past, the recent reports on computational mechanistic studies of the N-alkylation reactions, and the newly emerged N-alkylation methods based on novel alcohol activation protocols such as air-promoted reactions and transition metal-free methods, are also reviewed in this chapter. Problems and bottlenecks that remained to be solved in the field, and promising new research that deserves greater future attention and effort, are also reviewed and discussed.

Fungal strains as catalysts for the biotransformation of halolactones by hydrolytic dehalogenation with the dimethylcyclohexane system.

Science.gov (United States)

Grabarczyk, Małgorzata

2012-08-14

Bicyclic chloro-, bromo- and iodo-γ-lactones with dimethylcyclohexane rings were used as substrates for bioconversion by several fungal strains (Fusarium, Botrytis and Beauveria). Most of the selected microorganisms transformed these lactones by hydrolytic dehalogenation into the new compound cis-2-hydroxy-4,6-dimethyl-9-oxabicyclo[4.3.0]- nonan-8-one, mainly the (-)-isomer. When iodo-γ-lactone was used as the substrate, two products were observed: a hydroxy-γ-lactone and an unsaturated lactone. The structures of all substrates and products were established on the basis of their spectral data. The mechanism of dehalogenation of three halolactones was also studied.

A novel tandem Betti/Ullmann oxidation reaction as an efficient route ...

Indian Academy of Sciences (India)

Betti reaction; cross-coupling reaction; oxidation; heterogeneous catalysis. Abstract. A novel tandem Betti/Ullmann/oxidation reaction was used for synthesis of new oxazepine derivatives containing kojic acid. This protocol ... This method provides a new and useful strategy for the construction of heterocycles. Also novel Betti ...

Catalysis by Design: Well-Defined Single-Site Heterogeneous Catalysts

KAUST Repository

Pelletier, Jeremie

2016-03-09

ConspectusHeterogeneous catalysis, a field important industrially and scientifically, is increasingly seeking and refining strategies to render itself more predictable. The main issue is due to the nature and the population of catalytically active sites. Their number is generally low to very low, their "acid strengths" or " redox properties" are not homogeneous, and the material may display related yet inactive sites on the same material. In many heterogeneous catalysts, the discovery of a structure-activity reationship is at best challenging. One possible solution is to generate single-site catalysts in which most, if not all, of the sites are structurally identical. Within this context and using the right tools, the catalyst structure can be designed and well-defined, to reach a molecular understanding. It is then feasible to understand the structure-activity relationship and to develop predictable heterogeneous catalysis. Single-site well-defined heterogeneous catalysts can be prepared using concepts and tools of surface organometallic chemistry (SOMC). This approach operates by reacting organometallic compounds with surfaces of highly divided oxides (or of metal nanoparticles). This strategy has a solid track record to reveal structure-activity relationship to the extent that it is becoming now quite predictable. Almost all elements of the periodical table have been grafted on surfaces of oxides (from simple oxides such as silica or alumina to more sophisticated materials regarding composition or porosity).Considering catalytic hydrocarbon transformations, heterogeneous catalysis outcome may now be predicted based on existing mechanistic proposals and the rules of molecular chemistry (organometallic, organic) associated with some concepts of surface sciences. A thorough characterization of the grafted metal centers must be carried out using tools spanning from molecular organometallic or surface chemistry. By selection of the metal, its ligand set, and the

Multiscale Investigation on Biofilm Distribution and Its Impact on Macroscopic Biogeochemical Reaction Rates: BIOFILM DISTRIBUTION AND RATE SCALING

Energy Technology Data Exchange (ETDEWEB)

Yan, Zhifeng [Institute of Surface-Earth System Science, Tianjin University, Tianjin China; Pacific Northwest National Laboratory, Richland WA USA; Liu, Chongxuan [Pacific Northwest National Laboratory, Richland WA USA; School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen China; Liu, Yuanyuan [Pacific Northwest National Laboratory, Richland WA USA; School of Earth Science and Engineering, Nanjing University, Nanjing China; Bailey, Vanessa L. [Pacific Northwest National Laboratory, Richland WA USA

2017-11-01

Biofilms are critical locations for biogeochemical reactions in the subsurface environment. The occurrence and distribution of biofilms at microscale as well as their impacts on macroscopic biogeochemical reaction rates are still poorly understood. This paper investigated the formation and distributions of biofilms in heterogeneous sediments using multiscale models, and evaluated the effects of biofilm heterogeneity on local and macroscopic biogeochemical reaction rates. Sediment pore structures derived from X-ray computed tomography were used to simulate the microscale flow dynamics and biofilm distribution in the sediment column. The response of biofilm formation and distribution to the variations in hydraulic and chemical properties was first examined. One representative biofilm distribution was then utilized to evaluate its effects on macroscopic reaction rates using nitrate reduction as an example. The results revealed that microorganisms primarily grew on the surfaces of grains and aggregates near preferential flow paths where both electron donor and acceptor were readily accessible, leading to the heterogeneous distribution of biofilms in the sediments. The heterogeneous biofilm distribution decreased the macroscopic rate of biogeochemical reactions as compared with those in homogeneous cases. Operationally considering the heterogeneous biofilm distribution in macroscopic reactive transport models such as using dual porosity domain concept can significantly improve the prediction of biogeochemical reaction rates. Overall, this study provided important insights into the biofilm formation and distribution in soils and sediments as well as their impacts on the macroscopic manifestation of reaction rates.

Exchange reaction between hydrogen and deuterium. I. Importance of surface reactions in the steady-state mechanism

Energy Technology Data Exchange (ETDEWEB)

Marteau, C; Gaillard-Cusin, F; James, H [Centre National de la Recherche Scientifique, 45 - Orleans-la-Source (France). Centre de Recherches sur la Chimie de Combustion et des Hautes Temperatures

1978-05-01

Investigation of heterogeneous initiation process of gas phase linear chain reactions is carried out through the study of H/sub 2/-D/sub 2/ exchange reaction. Experimental data under study concern mainly the stationary rate of HD formation and the prestationary proceeding. Steady-state method accounts for the first one of these data; it allows to clearly compare the wall process part to the part played by the homogeneous chain reaction towards HD formation. Activation energy of exchange elementary step between chemisorbed hydrogen (on silica) and gaseous deuterium has been evaluated: Esub(e1)=52+-1 Kcal/mole.

Effect of reservoir heterogeneity on air injection performance in a light oil reservoir

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Hu Jia

2018-03-01

Full Text Available Air injection is a good option to development light oil reservoir. As well-known that, reservoir heterogeneity has great effect for various EOR processes. This also applies to air injection. However, oil recovery mechanisms and physical processes for air injection in heterogeneous reservoir with dip angle are still not well understood. The reported setting of reservoir heterogeneous for physical model or simulation model of air injection only simply uses different-layer permeability of porous media. In practice, reservoir heterogeneity follows the principle of geostatistics. How much of contrast in permeability actually challenges the air injection in light oil reservoir? This should be investigated by using layered porous medial settings of the classical Dykstra-Parsons style. Unfortunately, there has been no work addressing this issue for air injection in light oil reservoir. In this paper, Reservoir heterogeneity is quantified based on the use of different reservoir permeability distribution according to classical Dykstra-Parsons coefficients method. The aim of this work is to investigate the effect of reservoir heterogeneity on physical process and production performance of air injection in light oil reservoir through numerical reservoir simulation approach. The basic model is calibrated based on previous study. Total eleven pseudo compounders are included in this model and ten complexity of reactions are proposed to achieve the reaction scheme. Results show that oil recovery factor is decreased with the increasing of reservoir heterogeneity both for air and N2 injection from updip location, which is against the working behavior of air injection from updip location. Reservoir heterogeneity sometimes can act as positive effect to improve sweep efficiency as well as enhance production performance for air injection. High O2 content air injection can benefit oil recovery factor, also lead to early O2 breakthrough in heterogeneous reservoir. Well

Recent Advances in the Synthesis of N-Containing Heteroaromatics via Heterogeneously Transition Metal Catalysed Cross-Coupling Reactions

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Laurent Djakovitch

2011-06-01

Full Text Available N-containing heteroaromatics are important substructures found in numerous natural or synthetic alkaloids. The diversity of the structures encountered, as well as their biological and pharmaceutical relevance, have motivated research aimed at the development of new economical, efficient and selective synthetic strategies to access these compounds. Over more than 100 years of research, this hot topic has resulted in numerous so-called “classical synthetic methods” that have really contributed to this important area. However, when the selective synthesis of highly functional heteroaromatics like indoles, quinolones, indoxyls, etc. is considered these methods remain limited. Recently transition metal-catalysed (TM-catalysed procedures for the synthesis of such compounds and further transformations, have been developed providing increased tolerance toward functional groups and leading generally to higher reaction yields. Many of these methods have proven to be the most powerful and are currently applied in target- or diversity-oriented syntheses. This review article aims at reporting the recent developments devoted to this important area, focusing on the use of heterogeneous catalysed procedures that include either the formation of the heterocyclic ring towards the nuclei or their transformations to highly substituted compounds.

Regulating the surface of nanoceria and its applications in heterogeneous catalysis

Science.gov (United States)

Ma, Yuanyuan; Gao, Wei; Zhang, Zhiyun; Zhang, Sai; Tian, Zhimin; Liu, Yuxuan; Ho, Johnny C.; Qu, Yongquan

2018-03-01

Ceria (CeO2) as a support, additive, and active component for heterogeneous catalysis has been demonstrated to have great catalytic performance, which includes excellent thermal structural stability, catalytic efficiency, and chemoselectivity. Understanding the surface properties of CeO2 and the chemical reactions occurred on the corresponding interfaces is of great importance in the rational design of heterogeneous catalysts for various reactions. In general, the reversible Ce3+/Ce4+ redox pair and the surface acid-base properties contribute to the superior intrinsic catalytic capability of CeO2, and hence yield enhanced catalytic phenomenon in many reactions. Particularly, nanostructured CeO2 is characterized by a large number of surface-bound defects, which are primarily oxygen vacancies, as the surface active catalytic sites. Many efforts have therefore been made to control the surface defects and properties of CeO2 by various synthetic strategies and post-treatments. The present review provides a comprehensive overview of recent progress in regulating the surface structure and composition of CeO2 and its applications in catalysis.

Heterogeneous Risk Perceptions: The Case of Poultry Meat Purchase Intentions in Finland

OpenAIRE

Heikkil?, Jaakko; Pouta, Eija; Forsman-Hugg, Sari; M?kel?, Johanna

2013-01-01

This study focused on the heterogeneity of consumer reactions, measured through poultry meat purchase intentions, when facing three cases of risk. The heterogeneity was analysed by latent class logistic regression that included all three risk cases. Approximately 60% of the respondents belonged to the group of production risk avoiders, in which the intention to purchase risk food was significantly lower than in the second group of risk neutrals. In addition to socio-demographic variables, the...

A frame work for heat generation/absorption and modified homogeneous–heterogeneous reaction in flow based on non-Darcy–Forchheimer medium

Directory of Open Access Journals (Sweden)

Tasawar Hayat

2018-04-01

Full Text Available The present work aims to report the consequences of Darcy–Forchheimer medium in flow of Cross fluid model toward a stretched surface. Flow in porous space is categorized by Darcy–Forchheimer medium. Further heat transfer characteristics are examined via thermal radiation and heat generation/absorption. Transformation procedure is used. The arising system of nonlinear ordinary differential equations is solved numerically by means of shooting method. The effects of different flow variables on velocity, temperature, concentration, skin friction, and heat transfer rate are discussed. The obtained outcomes show that velocity was enhanced with the increase in the Weissenberg number but decays with increase in the porosity parameter and Hartman number. Temperature field is boosted by thermal radiation and heat generation; however, it decays with the increase in the Prandtl number. Keywords: Cross Fluid, Heat Generation/Absorption, Homogeneous–Heterogeneous Reactions, Non-Darcy–Forchheimer Medium, Thermal Radiation

Silicon improves seed germination and alleviates drought stress in lentil crops by regulating osmolytes, hydrolytic enzymes and antioxidant defense system.

Science.gov (United States)

Biju, Sajitha; Fuentes, Sigfredo; Gupta, Dorin

2017-10-01

Silicon (Si) has been widely reported to have beneficial effect on mitigating drought stress in plants. However, the effect of Si on seed germination under drought conditions is still poorly understood. This research was carried out to ascertain the role of Si to abate polyethylene glycol-6000 mediated drought stress on seed germination and seedling growth of lentil. Results showed that drought stress significantly decreased the seed germination traits and increased the concentration of osmolytes (proline, glycine betaine and soluble sugars), reactive oxygen species (hydrogen peroxide and superoxide anion) and lipid peroxides in lentil seedlings. The activities of hydrolytic enzymes and antioxidant enzymes increased significantly under osmotic stress. The application of Si significantly enhanced the plants ability to withstand drought stress conditions through increased Si content, improved antioxidants, hydrolytic enzymes activity, decreased concentration of osmolytes and reactive oxygen species. Multivariate data analysis showed statistically significant correlations among the drought-tolerance traits, whereas cluster analysis categorised the genotypes into distinct groups based on their drought-tolerance levels and improvements in expression of traits due to Si application. Thus, these results showed that Si supplementation of lentil was effective in alleviating the detrimental effects of drought stress on seed germination and increased seedling vigour. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

Inhibitors of the Hydrolytic Enzyme Dimethylarginine Dimethylaminohydrolase (DDAH: Discovery, Synthesis and Development

Directory of Open Access Journals (Sweden)

Rhys B. Murphy

2016-05-01

Full Text Available Dimethylarginine dimethylaminohydrolase (DDAH is a highly conserved hydrolytic enzyme found in numerous species, including bacteria, rodents, and humans. In humans, the DDAH-1 isoform is known to metabolize endogenous asymmetric dimethylarginine (ADMA and monomethyl arginine (l-NMMA, with ADMA proposed to be a putative marker of cardiovascular disease. Current literature reports identify the DDAH family of enzymes as a potential therapeutic target in the regulation of nitric oxide (NO production, mediated via its biochemical interaction with the nitric oxide synthase (NOS family of enzymes. Increased DDAH expression and NO production have been linked to multiple pathological conditions, specifically, cancer, neurodegenerative disorders, and septic shock. As such, the discovery, chemical synthesis, and development of DDAH inhibitors as potential drug candidates represent a growing field of interest. This review article summarizes the current knowledge on DDAH inhibition and the derived pharmacokinetic parameters of the main DDAH inhibitors reported in the literature. Furthermore, current methods of development and chemical synthetic pathways are discussed.

Synthesis and photoluminescent properties of yttrium vanadate phosphor prepared by the non-hydrolytic sol–gel process

Energy Technology Data Exchange (ETDEWEB)

Matos, Marcela G.; Faria, Emerson H. de; Rocha, Lucas A.; Calefi, Paulo S.; Ciuffi, Katia J. [Universidade de Franca, Av. Dr. Armando Salles Oliveira, 201 Franca, SP, CEP 14404-600 (Brazil); Nassar, Eduardo J., E-mail: ejnassar@unifran.br [Universidade de Franca, Av. Dr. Armando Salles Oliveira, 201 Franca, SP, CEP 14404-600 (Brazil); Sarmento, Victor Hugo Vitorino [Universidade Federal de Sergipe, Av. Ver. Olimpio Grande s/n Itabaiana, SE, CEP 49500-000 (Brazil)

2014-03-15

We used the non-hydrolytic sol–gel route to synthesize YVO{sub 4} crystalline phases doped with europium III ion. We heat-treated the samples at 600, 800, and 1000 °C and characterized the materials by thermal analysis, X-ray diffraction, small-angle X-ray scattering, and photoluminescence. Larger weight loss occurred until 500 °C, ascribed to removal of residual precursor molecules. X-ray diffraction patterns evidenced YVO{sub 4} phase formation at 600 °C. The crystallite size depended on the heat treatment temperature. SAXS showed that the nature of the system interfaces changed as a function of the thermal treatment. The excitation spectra of the samples displayed the charge transfer band. The photoluminescence data revealed the characteristic transition bands arising from the {sup 5}D{sub 0}→{sup 5}F{sub J} (J=0, 1, 2, 3, and 4) manifolds under maximum excitation at the charge transfer band and the {sup 5}L{sub 6} level of the Eu{sup 3+} ion. The {sup 5}D{sub 0}→{sup 7}F{sub 2} transition dominated the emission spectra, indicating that the Eu{sup 3+} ion occupies a site without inversion center. The lifetime and quantum efficiency values were about 0.70 ms and 50%, respectively, corroborating literature results. -- Highlights: • This study described the preparation of the yttrium vanadate by non-hydrolytic sol–gel. • The SAXS curves can be interpreted from the fractal theory for a two-phase model. • The goal of the work is the preparation of the phosphors at low temperature. • The lifetimes depend on wavelength of the excitation.

Thermomyces lanuginosus STm: a source of thermostable hydrolytic enzymes for novel application in extraction of high-quality natural rubber from Taraxacum kok-saghyz (rubber dandelion)

Science.gov (United States)

Hydrolytic enzymes from a newly isolated strain of the thermophilic fungus Thermomyces lanuginosus were used to extract rubber from Taraxacum kok-saghyz commonly known as rubber (or Russian or Kazak(h)) dandelion. The fungus was isolated from garden soil and identified as Thermomyces lanuginosus STm...

Analysis of heterogeneous oxygen exchange and fuel oxidation on the catalytic surface of perovskite membranes

KAUST Repository

Hong, Jongsup

2013-10-01

The catalytic kinetics of oxygen surface exchange and fuel oxidation for a perovskite membrane is investigated in terms of the thermodynamic state in the immediate vicinity of or on the membrane surface. Perovskite membranes have been shown to exhibit both oxygen perm-selectivity and catalytic activity for hydrocarbon conversion. A fundamental description of their catalytic surface reactions is needed. In this study, we infer the kinetic parameters for heterogeneous oxygen surface exchange and catalytic fuel conversion reactions, based on permeation rate measurements and a spatially resolved physical model that incorporates detailed chemical kinetics and transport in the gas-phase. The conservation equations for surface and bulk species are coupled with those of the gas-phase species through the species production rates from surface reactions. It is shown that oxygen surface exchange is limited by dissociative/associative adsorption/desorption of oxygen molecules onto/from the membrane surface. On the sweep side, while the catalytic conversion of methane to methyl radical governs the overall surface reactions at high temperature, carbon monoxide oxidation on the membrane surface is dominant at low temperature. Given the sweep side conditions considered in ITM reactor experiments, gas-phase reactions also play an important role, indicating the significance of investigating both homogeneous and heterogeneous chemistry and their coupling when examining the results. We show that the local thermodynamic state at the membrane surface should be considered when constructing and examining models of oxygen permeation and heterogeneous chemistry. © 2013 Elsevier B.V.

Analysis of heterogeneous oxygen exchange and fuel oxidation on the catalytic surface of perovskite membranes

KAUST Repository

Hong, Jongsup; Kirchen, Patrick; Ghoniem, Ahmed F.

2013-01-01

The catalytic kinetics of oxygen surface exchange and fuel oxidation for a perovskite membrane is investigated in terms of the thermodynamic state in the immediate vicinity of or on the membrane surface. Perovskite membranes have been shown to exhibit both oxygen perm-selectivity and catalytic activity for hydrocarbon conversion. A fundamental description of their catalytic surface reactions is needed. In this study, we infer the kinetic parameters for heterogeneous oxygen surface exchange and catalytic fuel conversion reactions, based on permeation rate measurements and a spatially resolved physical model that incorporates detailed chemical kinetics and transport in the gas-phase. The conservation equations for surface and bulk species are coupled with those of the gas-phase species through the species production rates from surface reactions. It is shown that oxygen surface exchange is limited by dissociative/associative adsorption/desorption of oxygen molecules onto/from the membrane surface. On the sweep side, while the catalytic conversion of methane to methyl radical governs the overall surface reactions at high temperature, carbon monoxide oxidation on the membrane surface is dominant at low temperature. Given the sweep side conditions considered in ITM reactor experiments, gas-phase reactions also play an important role, indicating the significance of investigating both homogeneous and heterogeneous chemistry and their coupling when examining the results. We show that the local thermodynamic state at the membrane surface should be considered when constructing and examining models of oxygen permeation and heterogeneous chemistry. © 2013 Elsevier B.V.

Estimating Reaction Rate Coefficients Within a Travel-Time Modeling Framework

Energy Technology Data Exchange (ETDEWEB)

Gong, R [Georgia Institute of Technology; Lu, C [Georgia Institute of Technology; Luo, Jian [Georgia Institute of Technology; Wu, Wei-min [Stanford University; Cheng, H. [Stanford University; Criddle, Craig [Stanford University; Kitanidis, Peter K. [Stanford University; Gu, Baohua [ORNL; Watson, David B [ORNL; Jardine, Philip M [ORNL; Brooks, Scott C [ORNL

2011-03-01

A generalized, efficient, and practical approach based on the travel-time modeling framework is developed to estimate in situ reaction rate coefficients for groundwater remediation in heterogeneous aquifers. The required information for this approach can be obtained by conducting tracer tests with injection of a mixture of conservative and reactive tracers and measurements of both breakthrough curves (BTCs). The conservative BTC is used to infer the travel-time distribution from the injection point to the observation point. For advection-dominant reactive transport with well-mixed reactive species and a constant travel-time distribution, the reactive BTC is obtained by integrating the solutions to advective-reactive transport over the entire travel-time distribution, and then is used in optimization to determine the in situ reaction rate coefficients. By directly working on the conservative and reactive BTCs, this approach avoids costly aquifer characterization and improves the estimation for transport in heterogeneous aquifers which may not be sufficiently described by traditional mechanistic transport models with constant transport parameters. Simplified schemes are proposed for reactive transport with zero-, first-, nth-order, and Michaelis-Menten reactions. The proposed approach is validated by a reactive transport case in a two-dimensional synthetic heterogeneous aquifer and a field-scale bioremediation experiment conducted at Oak Ridge, Tennessee. The field application indicates that ethanol degradation for U(VI)-bioremediation is better approximated by zero-order reaction kinetics than first-order reaction kinetics.

Study of the heterogeneous reaction of O3 with CH3SCH3 using the wetted-wall flowtube technique

Directory of Open Access Journals (Sweden)

M. Barcellos da Rosa

2003-01-01

Full Text Available This work presents the heterogeneous kinetics of the reaction of CH3SCH3 (dimethyl sulphide, DMS with O3 (ozone in aqueous solutions of different ionic strengths (0, 0.1 and 1.0M NaCl using the wetted-wall flowtube (WWFT technique. Henry's law coefficients of DMS on pure water and on different concentrations of NaCl (0.1M - 4.0M in the WWFT from UV spectrophotometric measurements of DMS in the gas phase, using a numerical transport model of phase exchange, were determined to be H ±s (M atm-1 = 2.16±0.5 at 274.4 K, 1.47±0.3 at 283.4 K, 0.72±0.2 at 291 K, 0.57±0.1 at 303.4 K and 0.33±0.1 at 313.4 K on water, on 1.0M NaCl to be H = 1.57±0.4 at 275.7 K, 0.8±0.2 at 291 K and on 4.0M NaCl to be H = 0.44±0.1 at 275.7 K and 0.16±0.04 at 291 K, showing a significant effect of ionic strength, m, on the solubility of DMS according to the equation ln (H/M atm-1 = 4061 T-1 - 0.052 m2 - 50.9 m T-1 - 14.0. At concentrations of DMS(liq above 50 mM, UV spectrophotometry of both O3(gas and DMS(gas enables us to observe simultaneously the reactive uptake of O3 on DMS solution and the gas-liquid equilibration of DMS along the WWFT. The uptake coefficient, g (gamma, of O3 on aqueous solutions of DMS, varying between 1 and 15·10-6, showed a square root-dependence on the aqueous DMS concentration (as expected for diffusive penetration into the surface film, where the reaction takes place in aqueous solution. The uptake coefficient was smaller on NaCl solution in accord with the lower solubility of O3. The heterogeneous reaction of O3(gas with DMS(liq was evaluated from the observations of the second order rate constant (kII for the homogeneous aqueous reaction O3(liq + DMS(liq using a numerical model of radial diffusion and reactive penetration, leading to kII ± D kII (in units of 108 M-1 s-1 = 4.1±1.2 at 291.0 K, 2.15±0.65 at 283.4 K and 1.8±0.5 at 274.4 K. Aside from the expected influence on solubility and aqueous-phase diffusion coefficient of both

Titanium Dioxide as a Catalyst Support in Heterogeneous Catalysis

Science.gov (United States)

Bagheri, Samira; Muhd Julkapli, Nurhidayatullaili; Bee Abd Hamid, Sharifah

2014-01-01

The lack of stability is a challenge for most heterogeneous catalysts. During operations, the agglomeration of particles may block the active sites of the catalyst, which is believed to contribute to its instability. Recently, titanium oxide (TiO2) was introduced as an alternative support material for heterogeneous catalyst due to the effect of its high surface area stabilizing the catalysts in its mesoporous structure. TiO2 supported metal catalysts have attracted interest due to TiO2 nanoparticles high activity for various reduction and oxidation reactions at low pressures and temperatures. Furthermore, TiO2 was found to be a good metal oxide catalyst support due to the strong metal support interaction, chemical stability, and acid-base property. The aforementioned properties make heterogeneous TiO2 supported catalysts show a high potential in photocatalyst-related applications, electrodes for wet solar cells, synthesis of fine chemicals, and others. This review focuses on TiO2 as a support material for heterogeneous catalysts and its potential applications. PMID:25383380

Heterogeneous catalytic materials solid state chemistry, surface chemistry and catalytic behaviour

CERN Document Server

Busca, Guido

2014-01-01

Heterogeneous Catalytic Materials discusses experimental methods and the latest developments in three areas of research: heterogeneous catalysis; surface chemistry; and the chemistry of catalysts. Catalytic materials are those solids that allow the chemical reaction to occur efficiently and cost-effectively. This book provides you with all necessary information to synthesize, characterize, and relate the properties of a catalyst to its behavior, enabling you to select the appropriate catalyst for the process and reactor system. Oxides (used both as catalysts and as supports for cata

Synthesis of biodiesel using local natural zeolite as heterogeneous anion exchange catalyst

Science.gov (United States)

Hartono, R.; Wijanarko, A.; Hermansyah, H.

2018-04-01

Production of biodiesel using homogen catalyst: alkaline catalysts, acid catalysts, biocatalysts, and supercritical methanol are very inefficient, because these catalysts have a very high cost production of biodiesel and non-ecofriendly. The heterogeneous catalyst is then used to avoid adverse reaction of biodiesel production. The heterogeneous catalysts used is ion exchanger using natural zeolit catalists bayah banten (ZABBrht) and macroporous lewatit that can be used to produce biodiesel in the solid phase so that the separation is easier and can be used repeatedly. The results of biodiesel reach its optimum in engineering ion exchange catalyst natural zeolit bayah and macroporous lewatit which has been impregnated and calcinated at temperature 60 °C at reaction time 2 hours, are 94.8% and 95.24%, using 100 gr.KOH/100 mL Aquadest.

Rape oil transesterification over heterogeneous catalysts

Energy Technology Data Exchange (ETDEWEB)

Encinar, J.M.; Martinez, G. [Dpto. Ingenieria Quimica y Quimica Fisica, UEX, Avda. Elvas s/n, 06071-Badajoz (Spain); Gonzalez, J.F. [Dpto. Fisica Aplicada, UEX, Avda Elvas s/n, 06071-Badajoz (Spain); Pardal, A. [Dpto. Ciencias do Ambiente, ESAB, IPBeja, Rua Pedro Soares s/n, 7800-Beja (Portugal)

2010-11-15

This work studies the application of KNO{sub 3}/CaO catalyst in the transesterification reaction of triglycerides with methanol. The objective of the work was characterizing the methyl esters for its use as biodiesel in compression ignition motors. The variables affecting the methyl ester yield during the transesterification reaction, such as, amount of KNO{sub 3} impregnated in CaO, the total catalyst content, reaction temperature, agitation rate, and the methanol/oil molar ratio, were investigated to optimize the reaction conditions. The evolution of the process was followed by gas chromatography, determining the concentration of the methyl esters at different reaction times. The biodiesel was characterized by its density, viscosity, cetane index, saponification value, iodine value, acidity index, CFPP (cold filter plugging point), flash point and combustion point, according to ISO norms. The results showed that calcium oxide, impregnated with KNO{sub 3}, have a strong basicity and high catalytic activity as a heterogeneous solid base catalyst. The biodiesel with the best properties was obtained using an amount of KNO{sub 3} of 10% impregnated in CaO, a methanol/oil molar ratio of 6:1, a reaction temperature of 65 C, a reaction time of 3.0 h, and a catalyst total content of 1.0%. In these conditions, the oil conversion was 98% and the final product obtained had very similar characteristics to a no. 2 diesel, and therefore, these methyl esters might be used as an alternative to fossil fuels. (author)

Heterogeneously catalyzed reactive extraction for biomass valorization into chemicals and fuels

NARCIS (Netherlands)

Ordomskiy, V.; Khodakov, A.Y.; Nijhuis, T.A.; Schouten, J.C.

2015-01-01

This paper focuses on the heterogeneously catalyzed reactive extraction and separation in reaction steps in organic and aqueous phases during the transformation of biomass derived products. Two approaches are demonstrated for decomposing and preserving routes for biomass transformation into valuable

Catalytic reactions of synthesis gas. Part 2. Methanol carbonylation and homologation

Energy Technology Data Exchange (ETDEWEB)

Niemelae, M.

1993-01-01

The aim of the review is to evaluate the applicability of methanol hydrocarbonylation as a second test reaction to study the nondissociative activation of CO by heterogeneous rhodium and cobalt catalysts. The main emphasis in methanol (hydro)carbonylation chemistry has been on homogeneous reactions. These systems have been seen advantageous in selectivity, activity and ease of modification. The heterogenization attempts have been carried out to obtain easier separation of the catalyst and the product. The activity of cobalt, rhodium and other metals supported on different materials have been studied in heterogeneous methanol (hydro)carbonylation. The observed activities have been considerably influenced by the support. The most effective catalyst support has been activated carbon. Good carbonylation activities and selectivities have also been observed in conjunction with zeolite supports. The literature study indicates that the typical experimental conditions of methanol (hydro)carbonylation do not exceed the constructional and operational limits of the available reactor system, i.e. 500 C and 50 bar. The reaction is suitable for testing Co and Rh precursors, since both cobalt and rhodium compounds have shown carbonylation activity.

Heterogeneously Catalysed Aldol Reactions in Supercritical Carbon Dioxide as Innovative and Non-Flammable Reaction Medium

DEFF Research Database (Denmark)

Musko, Nikolai; Grunwaldt, Jan-Dierk

2011-01-01

Aldol reactions of several aldehydes have been investigated over acidic and basic catalysts in supercritical carbon dioxide at 180 bar and 100 °C. Both acidic (Amberlyst-15, tungstosilicic acid (TSA) on SiO2 and MCM-41) and basic (hydrotalcite) materials showed interesting performance in this pre...

Development of Molecular Catalysts to Bridge the Gap between Heterogeneous and Homogeneous Catalysts

Science.gov (United States)

Ye, Rong

Catalysts, heterogeneous, homogeneous, and enzymatic, are comprised of nanometer-sized inorganic and/or organic components. They share molecular factors including charge, coordination, interatomic distance, bonding, and orientation of catalytically active atoms. By controlling the governing catalytic components and molecular factors, catalytic processes of a multichannel and multiproduct nature could be run in all three catalytic platforms to create unique end-products. Unifying the fields of catalysis is the key to achieving the goal of 100% selectivity in catalysis. Recyclable catalysts, especially those that display selective reactivity, are vital for the development of sustainable chemical processes. Among available catalyst platforms, heterogeneous catalysts are particularly well-disposed toward separation from the reaction mixture via filtration methods, which renders them readily recyclable. Furthermore, heterogeneous catalysts offer numerous handles - some without homogeneous analogues - for performance and selectivity optimization. These handles include nanoparticle size, pore profile of porous supports, surface ligands and interface with oxide supports, and flow rate through a solid catalyst bed. Despite these available handles, however, conventional heterogeneous catalysts are themselves often structurally heterogeneous compared to homogeneous catalysts, which complicates efforts to optimize and expand the scope of their reactivity and selectivity. Ongoing efforts are aimed to address the above challenge by heterogenizing homogeneous catalysts, which can be defined as the modification of homogeneous catalysts to render them in a separable (solid) phase from the starting materials and products. Specifically, we grow the small nanoclusters in dendrimers, a class of uniform polymers with the connectivity of fractal trees and generally radial symmetry. Thanks to their dense multivalency, shape persistence and structural uniformity, dendrimers have proven to

Application of personal computers to study the kinetics of heterogeneous isotopic exchange

International Nuclear Information System (INIS)

Koernyei, Jozsef; Lakatos, Mihaly

1985-01-01

The kinetics of some heterogeneous isotopic exchange reactions of alkaline metal ions between solid (crystalline zirconium phosphate) and liquid phases were investigated. Ion diffusion in solid phase was considered as rate controlling step. The Laplace transformation solution of Fick's II law was used with a Sinclair ZX Spectrum personal computer. In some cases the exchange reaction should be regarded as a superposition of diffusion and a first order process. (author)

Heterogeneous Fenton-like discoloration of methyl orange using Fe3O4/MWCNTs as catalyst: kinetics and Fenton-like mechanism

Science.gov (United States)

Xu, Huan-Yan; Wang, Yuan; Shi, Tian-Nuo; Zhao, Hang; Tan, Qu; Zhao, Bo-Chao; He, Xiu-Lan; Qi, Shu-Yan

2018-03-01

The kinetics and Fenton-like mechanism are two challenging tasks for heterogeneous Fenton-like catalytic oxidation of organic pollutants. In this study, three kinetic models were used for the kinetic studies of Fe3O4/MWCNTs-H2O2 Fenton-like reaction for MO degradation. The results indicated that this reaction followed the first-order kinetic model. The relationship of reaction rate constant and temperature followed the Arrhenius equation. The activation energy and frequency factor of this system were calculated as 8.2 kJ·mol-1 and 2.72 s-1, respectively. The quantifications of Fe ions dissolution and •OH radicals generation confirmed that the homogeneous and heterogeneous catalyses were involved in Fe3O4/MWCNTs-H2O2 Fenton-like reaction. The reaction rate constant was closely related with Fe ions dissolution and •OH radicals generation. Fe3O4/MWCNTs nanocomposites had typical ferromagnetic property and could be easily separated from solution by an external magnet after being used. Furthermore, Fe3O4/MWCNTs nanocomposites exhibited good stability and recyclability. Finally, the Fenton-like mechanisms on homogeneous and heterogeneous catalyses were described.

Hydrolytic and thermal degradation of PCL and PCL/Bentonite compounds

Energy Technology Data Exchange (ETDEWEB)

Franca, Danyelle Campos; Bezerra, Elieber Barros; Morais, Dayanne Diniz de Souza; Araujo, Edcleide Maria [Universidade Federal de Campina grande (UFCG), PB (Brazil). Departamento de Engenharia de Materiais; Wellen, Renate Maria Ramos, E-mail: wellen.renate@gmail.com [Universidade Federal da Paraiba (UFPB), Joao Pessoa, PB (Brazil). Departamento de Engenharia de Materiais

2016-05-15

Poly(ε-caprolactone)/montmorillonite (PCL/MMT) and Poly(εcaprolactone)/organo-modified montmorillonite (PCL/OMMT) compounds at 3% w/w clay content were prepared by melting mixing. The effect of MMT and OMMT on the degradability of PCL injected specimens was investigated in vacuum at 40 deg C for up to 45 days and in aqueous medium at 40 deg C for up to 45 days. Selected specimens were collected after 15, 30 and 45 days of exposure. Microstructural changes were monitored during the degradation experiment by means of melt flow rate (MFR), weight loss, X ray diffraction (XRD), mechanical properties, and scanning electron microscopy (SEM). PCL and its compounds revealed not to be prone to hydrolytic degradation with similar results for MFR of samples exposed in vacuum and water. Gain and loss of weight were observed during experiments, probably due to swelling mechanism taking place in two stages, with the amorphous phase being the first to be swelled followed by the crystalline one. By XRD a new peak corresponding to (002) plane was evident for PCL/OMMT. PCL proved to be resistant to degradation since experiments carried out in vacuum or in aqueous medium for up to 45 days were not enough to affect the mechanical integrity of PCL samples. (author)

Hydrolytic and thermal degradation of PCL and PCL/Bentonite compounds

International Nuclear Information System (INIS)

Franca, Danyelle Campos; Bezerra, Elieber Barros; Morais, Dayanne Diniz de Souza; Araujo, Edcleide Maria; Wellen, Renate Maria Ramos

2016-01-01

Poly(ε-caprolactone)/montmorillonite (PCL/MMT) and Poly(εcaprolactone)/organo-modified montmorillonite (PCL/OMMT) compounds at 3% w/w clay content were prepared by melting mixing. The effect of MMT and OMMT on the degradability of PCL injected specimens was investigated in vacuum at 40 deg C for up to 45 days and in aqueous medium at 40 deg C for up to 45 days. Selected specimens were collected after 15, 30 and 45 days of exposure. Microstructural changes were monitored during the degradation experiment by means of melt flow rate (MFR), weight loss, X ray diffraction (XRD), mechanical properties, and scanning electron microscopy (SEM). PCL and its compounds revealed not to be prone to hydrolytic degradation with similar results for MFR of samples exposed in vacuum and water. Gain and loss of weight were observed during experiments, probably due to swelling mechanism taking place in two stages, with the amorphous phase being the first to be swelled followed by the crystalline one. By XRD a new peak corresponding to (002) plane was evident for PCL/OMMT. PCL proved to be resistant to degradation since experiments carried out in vacuum or in aqueous medium for up to 45 days were not enough to affect the mechanical integrity of PCL samples. (author)

Monitoring mass transport in heterogeneously catalyzed reactions by field-gradient NMR for assessing reaction efficiency in a single pellet

Science.gov (United States)

Buljubasich, L.; Blümich, B.; Stapf, S.

2011-09-01

An important aspect in assessing the performance of a catalytically active reactor is the accessibility of the reactive sites inside the individual pellets, and the mass transfer of reactants and products to and from these sites. Optimal design often requires a suitable combination of micro- and macropores in order to facilitate mass transport inside the pellet. In an exothermic reaction, fluid exchange between the pellet and the surrounding medium is enhanced by convection, and often by the occurrence of gas bubbles. Determining mass flow in the vicinity of a pellet thus represents a parameter for quantifying the reaction efficiency and its dependence on time or external reaction conditions. Field gradient Nuclear Magnetic Resonance (NMR) methods are suggested as a tool for providing parameters sensitive to this mass flow in a contact-free and non-invasive way. For the example of bubble-forming hydrogen peroxide decomposition in an alumina pellet, the dependence of the mean-squared displacement of fluid molecules on spatial direction, observation time and reaction time is presented, and multi-pulse techniques are employed in order to separate molecular displacements from coherent and incoherent motion on the timescale of the experiment. The reaction progress is followed until the complete decomposition of H 2O 2.

Formation of high-molecular-weight compounds via the heterogeneous reactions of gaseous C8-C10 n-aldehydes in the presence of atmospheric aerosol components

Science.gov (United States)

Han, Yuemei; Kawamura, Kimitaka; Chen, Qingcai; Mochida, Michihiro

2016-02-01

A laboratory study on the heterogeneous reactions of straight-chain aldehydes was performed by exposing n-octanal, nonanal, and decanal vapors to ambient aerosol particles. The aerosol and blank filters were extracted using methanol. The extracts were nebulized and the resulting compositions were examined using a high-resolution time-of-flight aerosol mass spectrometer. The mass spectral analysis showed that the exposures of the aldehydes to aerosol samples increased the peak intensities in the high mass range. The peaks in the mass spectra of the aerosol samples after exposure to different aldehydes were characterized by a homologous series of peak shifts due to the addition of multiple CH2 units. This result is explained by the formation of high-molecular-weight (HMW) compounds that contain single or multiple aldehyde moieties. The HMW fragment peaks for the blank filters exposed to n-aldehydes were relatively weak, indicating an important contribution from the ambient aerosol components to the formation of the HMW compounds. Among the factors affecting the overall interaction of aldehydes with atmospheric aerosol components, gas phase diffusion possibly limited the reactions under the studied conditions; therefore, their occurrence to a similar degree in the atmosphere is not ruled out, at least for the reactions involving n-nonanal and decanal. The major formation pathways for the observed HMW products may be the self-reactions of n-aldehydes mediated by atmospheric aerosol components and the reactions of n-aldehydes with organic aerosol components. The observed formation of HMW compounds encourages further investigations into their effects on the aerosol properties as well as the organic aerosol mass in the atmosphere.

Role of bonding mechanisms during transfer hydrogenation reaction on heterogeneous catalysts of platinum nanoparticles supported on zinc oxide nanorods

Science.gov (United States)

Al-Alawi, Reem A.; Laxman, Karthik; Dastgir, Sarim; Dutta, Joydeep

2016-07-01

For supported heterogeneous catalysis, the interface between a metal nanoparticle and the support plays an important role. In this work the dependency of the catalytic efficiency on the bonding chemistry of platinum nanoparticles supported on zinc oxide (ZnO) nanorods is studied. Platinum nanoparticles were deposited on ZnO nanorods (ZnO NR) using thermal and photochemical processes and the effects on the size, distribution, density and chemical state of the metal nanoparticles upon the catalytic activities are presented. The obtained results indicate that the bonding at Pt-ZnO interface depends on the deposition scheme which can be utilized to modulate the surface chemistry and thus the activity of the supported catalysts. Additionally, uniform distribution of metal on the catalyst support was observed to be more important than the loading density. It is also found that oxidized platinum Pt(IV) (platinum hydroxide) provided a more suitable surface for enhancing the transfer hydrogenation reaction of cyclohexanone with isopropanol compared to zero valent platinum. Photochemically synthesized ZnO supported nanocatalysts were efficient and potentially viable for upscaling to industrial applications.

Studies of Heterogeneously Catalyzed Liquid-Phase Alcohol Oxidation on Platinum bySum-frequency Generation Vibrational Spectroscopy and Reaction Rate Measurements

Energy Technology Data Exchange (ETDEWEB)

Thompson, Christopher [Univ. of California, Berkeley, CA (United States)

2014-05-15

Compared to many branches of chemistry, the molecular level study of catalytically active surfaces is young. Only with the invention of ultrahigh vacuum technology in the past half century has it been possible to carry out experiments that yield useful molecular information about the reactive occurrences at a surface. The reason is two-fold: low pressure is necessary to keep a surface clean for an amount of time long enough to perform an experiment, and most atomic scale techniques that are surface speci c (x-ray photoelectron spectroscopy, electron energy loss spectroscopy, Auger electron spectroscopy, etc.) cannot be used at ambient pressures, because electrons, which act as chemical probes in these techniques, are easily scattered by molecules. Sum-frequency generation (SFG) vibrational spectroscopy is one technique that can provide molecular level information from the surface without the necessity for high vacuum. Since the advent of SFG as a surface spectroscopic tool it has proved its worth in the studies of surface catalyzed reactions in the gas phase, with numerous reactions in the gas phase having been investigated on a multitude of surfaces. However, in situ SFG characterization of catalysis at the solid-liquid interface has yet to be thoroughly pursued despite the broad interest in the use of heterogeneous catalysts in the liquid phase as replacements for homogeneous counterparts. This work describes an attempt to move in that direction, applying SFG to study the solid-liquid interface under conditions of catalytic alcohol oxidation on platinum.

Heterogeneous Catalysis of Polyoxometalate Based Organic–Inorganic Hybrids

Directory of Open Access Journals (Sweden)

Yuanhang Ren

2015-03-01

Full Text Available Organic–inorganic hybrid polyoxometalate (POM compounds are a subset of materials with unique structures and physical/chemical properties. The combination of metal-organic coordination complexes with classical POMs not only provides a powerful way to gain multifarious new compounds but also affords a new method to modify and functionalize POMs. In parallel with the many reports on the synthesis and structure of new hybrid POM compounds, the application of these compounds for heterogeneous catalysis has also attracted considerable attention. The hybrid POM compounds show noteworthy catalytic performance in acid, oxidation, and even in asymmetric catalytic reactions. This review summarizes the design and synthesis of organic–inorganic hybrid POM compounds and particularly highlights their recent progress in heterogeneous catalysis.

The impact of heterogeneous response on coupled spreading dynamics in multiplex networks

Science.gov (United States)

Nie, Xiaoyu; Tang, Ming; Zou, Yong; Guan, Shuguang; Zhou, Jie

2017-10-01

Many recent studies have demonstrated that individual awareness of disease may significantly affect the spreading process of infectious disease. In the majority of these studies, the response of the awareness is generally treated homogeneously. Considering of diversity and heterogeneity in the human behavior which widely exist under different circumstances, in this paper we study heterogeneous response when people are aware of the prevalence of infectious diseases. Specifically, we consider that an individual with more neighbors may take more preventive measures as a reaction when he is aware of the disease. A suppression strength is introduced to describe such heterogeneity, and we find that a more evident heterogeneity may cause a more effective suppressing effect to the spreading of epidemics. A mean-field theory is developed to support the results which are verified on the multiplex networks with different interlayer degree correlation.

Heterogeneous risk perceptions: the case of poultry meat purchase intentions in Finland.

Science.gov (United States)

Heikkilä, Jaakko; Pouta, Eija; Forsman-Hugg, Sari; Mäkelä, Johanna

2013-10-11

This study focused on the heterogeneity of consumer reactions, measured through poultry meat purchase intentions, when facing three cases of risk. The heterogeneity was analysed by latent class logistic regression that included all three risk cases. Approximately 60% of the respondents belonged to the group of production risk avoiders, in which the intention to purchase risk food was significantly lower than in the second group of risk neutrals. In addition to socio-demographic variables, the purchase intentions were statistically associated with several attitude-based variables. We highlighted some policy implications of the heterogeneity. Overall, the study demonstrated that risk matters to consumers, not all risk is equal, and consumer types react somewhat differently to different types of risk.

Determination of the enzyme reaction rate in a differential fixed-bed reactor: a case study

Directory of Open Access Journals (Sweden)

Baruque Filho E.A.

2001-01-01

Full Text Available The reaction rate of starch hydrolysis catalyzed by a glucoamylase covalently bound to chitin particles was measured in a Differential Fixed-Bed Reactor (DFBR. Under selected test conditions the initial reaction rate may represent biocatalyst activity. Some aspects which influence measurement of the initial reaction rate of an immobilized enzyme were studied: the amount of desorbed enzyme and its hydrolytic activity, the extent of pore blockage of the biocatalyst caused by substrate solution impurities and the internal and external diffusional mass transfer effects. The results showed that the enzyme glucoamylase was firmly bound to the support, as indicated by the very low amount of desorbed protein found in the recirculating liquid. Although this protein was very active, its contribution to the overall reaction rate was negligible. It was observed that the biocatalyst pores were susceptible to being blocked by the impurities of the starch solution. This latter effect was accumulative, increasing with the number of sequential experiments carried out. When the substrate solution was filtered before use, very reliable determinations of immobilized enzyme reaction rates could be performed in the DFBR. External and internal diffusional resistences usually play a significant role in fixed-bed reactors. However, for the experimental system studied, internal mass transfer effects were not significant, and it was possible to select an operational condition (recirculation flow rate value that minimized the external diffusional limitations.

Fungal Strains as Catalysts for the Biotransformation of Halolactones by Hydrolytic Dehalogenation with the Dimethylcyclohexane System

Directory of Open Access Journals (Sweden)

Małgorzata Grabarczyk

2012-08-01

Full Text Available Bicyclic chloro-, bromo- and iodo-γ-lactones with dimethylcyclohexane rings were used as substrates for bioconversion by several fungal strains (Fusarium, Botrytis and Beauveria. Most of the selected microorganisms transformed these lactones by hydrolytic dehalogenation into the new compound cis-2-hydroxy-4,6-dimethyl-9-oxabicyclo[4.3.0]- nonan-8-one, mainly the (−-isomer. When iodo-γ-lactone was used as the substrate, two products were observed: a hydroxy-γ-lactone and an unsaturated lactone. The structures of all substrates and products were established on the basis of their spectral data. The mechanism of dehalogenation of three halolactones was also studied.

Biodiesel production from castor oil using heterogeneous Ni doped ZnO nanocatalyst.

Science.gov (United States)

Baskar, G; Aberna Ebenezer Selvakumari, I; Aiswarya, R

2018-02-01

In the present study, castor oil with high free fatty acid was used for biodiesel production using heterogeneous Ni doped ZnO nanocatalyst. Ni doped ZnO nanocomposite calcinated at 800 °C has shown better catalytic activity. Process parameters on heterogeneous catalysis of castor oil into biodiesel were optimized using conventional and Response Surface Methodology (RSM). RSM was found more accurate in estimating the optimum conditions with higher biodiesel yield (95.20%). The optimum conditions for transesterification was found to be oil to methanol molar ratio of 1:8, catalyst loading 11% (w/w), reaction temperature of 55 °C for 60 min of reaction time by response surface method. The reusability studies showed that the nanocatalyst can be reused efficiently for 3 cycles. Copyright © 2017 Elsevier Ltd. All rights reserved.

An advanced method of heterogeneous reactor theory

International Nuclear Information System (INIS)

Kochurov, B.P.

1994-08-01

Recent approaches to heterogeneous reactor theory for numerical applications were presented in the course of 8 lectures given in JAERI. The limitations of initial theory known after the First Conference on Peacefull Uses of Atomic Energy held in Geneva in 1955 as Galanine-Feinberg heterogeneous theory:-matrix from of equations, -lack of consistent theory for heterogeneous parameters for reactor cell, -were overcome by a transformation of heterogeneous reactor equations to a difference form and by a development of a consistent theory for the characteristics of a reactor cell based on detailed space-energy calculations. General few group (G-number of groups) heterogeneous reactor equations in dipole approximation are formulated with the extension of two-dimensional problem to three-dimensions by finite Furie expansion of axial dependence of neutron fluxes. A transformation of initial matrix reactor equations to a difference form is presented. The methods for calculation of heterogeneous reactor cell characteristics giving the relation between vector-flux and vector-current on a cell boundary are based on a set of detailed space-energy neutron flux distribution calculations with zero current across cell boundary and G calculations with linearly independent currents across the cell boundary. The equations for reaction rate matrices are formulated. Specific methods were developed for description of neutron migration in axial and radial directions. The methods for resonance level's approach for numerous high-energy resonances. On the basis of these approaches the theory, methods and computer codes were developed for 3D space-time react or problems including simulation of slow processes with fuel burn-up, control rod movements, Xe poisoning and fast transients depending on prompt and delayed neutrons. As a result reactors with several thousands of channels having non-uniform axial structure can be feasibly treated. (author)

2013 Gordon Research Conference, Inorganic reaction mechanisms, Galveston, TX, March 3-8 2013

Energy Technology Data Exchange (ETDEWEB)

Abu-Omar, Mahdi M. [Purdue Univ., West Lafayette, IN (United States)

2012-12-08

The 2013 Gordon Conference on Inorganic Reaction Mechanisms will present cutting-edge research on the molecular aspects of inorganic reactions involving elements from throughout the periodic table and state-of-the art techniques that are used in the elucidation of reaction mechanisms. The Conference will feature a wide range of topics, such as homogeneous and heterogeneous catalysis, metallobiochemistry, electron-transfer in energy reactions, polymerization, nitrogen fixation, green chemistry, oxidation, solar conversion, alkane functionalization, organotransition metal chemistry, and computational chemistry. The talks will cover themes of current interest including energy, materials, and bioinorganic chemistry. Sections cover: Electron-Transfer in Energy Reactions; Catalytic Polymerization and Oxidation Chemistry; Kinetics and Spectroscopy of Heterogeneous Catalysts; Metal-Organic Chemistry and its Application in Synthesis; Green Energy Conversion;Organometallic Chemistry and Activation of Small Molecules; Advances in Kinetics Modeling and Green Chemistry; Metals in Biology and Disease; Frontiers in Catalytic Bond Activation and Cleavage.

Effective dynamics along given reaction coordinates, and reaction rate theory.

Science.gov (United States)

Zhang, Wei; Hartmann, Carsten; Schütte, Christof

2016-12-22

In molecular dynamics and related fields one considers dynamical descriptions of complex systems in full (atomic) detail. In order to reduce the overwhelming complexity of realistic systems (high dimension, large timescale spread, limited computational resources) the projection of the full dynamics onto some reaction coordinates is examined in order to extract statistical information like free energies or reaction rates. In this context, the effective dynamics that is induced by the full dynamics on the reaction coordinate space has attracted considerable attention in the literature. In this article, we contribute to this discussion: we first show that if we start with an ergodic diffusion process whose invariant measure is unique then these properties are inherited by the effective dynamics. Then, we give equations for the effective dynamics, discuss whether the dominant timescales and reaction rates inferred from the effective dynamics are accurate approximations of such quantities for the full dynamics, and compare our findings to results from approaches like Mori-Zwanzig, averaging, or homogenization. Finally, by discussing the algorithmic realization of the effective dynamics, we demonstrate that recent algorithmic techniques like the "equation-free" approach and the "heterogeneous multiscale method" can be seen as special cases of our approach.

Hydrolytic enzyme activities in shiitake mushroom (Lentinula edodes) strains cultivated on coffee pulp.

Science.gov (United States)

Mata, Gerardo; Salmones, Dulce; Pérez-Merlo, Rosalía

Hydrolytic enzyme production (cellulases, laminarinases and xylanases) was studied in cultures of Lentinula edodes on sterilized coffee pulp. Samples of substrate colonized by mycelia were taken after 7, 14, 21, 28 and 35 days of incubation at 25°C (W1 to W5) and during the fruiting period at different stages: formation of primordia (PF), first harvest (H) and one week after the first harvest (PH). The enzymatic activity was lower during the early mycelial growth and showed higher levels during the formation and development of fruiting bodies. During the reproductive stage of the fungus, the samples were subjected to a soaking treatment; however, it was not possible to relate this soaking treatment to the increase in enzyme production. The levels of enzymatic activity suggest that secretion of the studied enzymes does not influence the adaptability of the strains to the substrate. Copyright © 2016 Asociación Argentina de Microbiología. Publicado por Elsevier España, S.L.U. All rights reserved.

Biogas production from brewery spent grain enhanced by bioaugmentation with hydrolytic anaerobic bacteria.

Science.gov (United States)

Čater, Maša; Fanedl, Lijana; Malovrh, Špela; Marinšek Logar, Romana

2015-06-01

Lignocellulosic substrates are widely available but not easily applied in biogas production due to their poor anaerobic degradation. The effect of bioaugmentation by anaerobic hydrolytic bacteria on biogas production was determined by the biochemical methane potential assay. Microbial biomass from full scale upflow anaerobic sludge blanket reactor treating brewery wastewater was a source of active microorganisms and brewery spent grain a model lignocellulosic substrate. Ruminococcus flavefaciens 007C, Pseudobutyrivibrio xylanivorans Mz5(T), Fibrobacter succinogenes S85 and Clostridium cellulovorans as pure and mixed cultures were used to enhance the lignocellulose degradation and elevate the biogas production. P. xylanivorans Mz5(T) was the most successful in elevating methane production (+17.8%), followed by the coculture of P. xylanivorans Mz5(T) and F. succinogenes S85 (+6.9%) and the coculture of C. cellulovorans and F. succinogenes S85 (+4.9%). Changes in microbial community structure were detected by fingerprinting techniques. Copyright © 2015 Elsevier Ltd. All rights reserved.

Spatial coupling in heterogeneous catalysis

Science.gov (United States)

Yamamoto, S. Y.; Surko, C. M.; Maple, M. B.

1995-11-01

Spatial coupling mechanisms are studied in the heterogeneous catalytic oxidation of carbon monoxide over platinum at atmospheric pressure under oscillatory conditions. Experiments are conducted in a continuous flow reactor, and the reaction rate is monitored using both infrared imaging and thermocouples. The catalysts are in the form of platinum annular thin films on washer-shaped quartz substrates, and they provide highly repeatable oscillatory behavior. Oscillations are typically spatially synchronized with the entire catalyst ``flashing'' on and off uniformly. Spatial coupling is investigated by introducing various barriers which split the annular ring in half. Infrared images show that coupling through the gas phase dominates coupling via the diffusion of CO on the surface or heat diffusion through the substrate. The introduction of a localized heat perturbation to the catalyst surface does not induce a transition in the reaction rate. Thus, it is likely that the primary mode of communication is through the gas-phase diffusion of reactants.

Dynamic effects of increasing heterogeneity in financial markets

International Nuclear Information System (INIS)

Naimzada, Ahmad K.; Ricchiuti, Giorgio

2009-01-01

Despite canonical behavioural financial market models [Day R, Huang W. Bulls, bears and market sheep. J Econ Behav Org 1990;14:299-329], that use different types of agents (i.e., fundamentalist vs. chartists), we develop a model in which the source of instability is the interaction of groups that are homogeneous in the strategy they use, but have heterogeneous beliefs about the fundamental value of the asset. Specifically, heterogeneity arises among two groups of fundamentalists that follow gurus. We show that an increasing distance between beliefs (the degree of heterogeneity), leads first (i) to a pitchfork bifurcation to arise secondly (ii) it generates, together with a larger reaction to misalignment of both market maker and agents, the appearance of a periodic, or even, chaotic, price fluctuation; (iii) finally a homoclinic bifurcation [Dieci R, Bischi GI, Gardini L. From bi-stability to chaotic oscillations in a macroeconomic model. Chaos, Solitons and Fractals 2001;12:805-22] transforms a two piece chaotic set into a one piece chaotic set that generates bull and bear markets.

Effects of solution viscosity on heterogeneous electron transfer across a liquid/liquid interface

Energy Technology Data Exchange (ETDEWEB)

Bai Yamin; Sun Peng; Zhang Meiqin; Gao Zhao; Yang Zhengyu; Shao Yuanhua

2003-10-15

Scanning electrochemical microscopy (SECM) is employed to investigate the effect of solution viscosity on the rate constants of electron transfer (ET) reaction between potassium ferricyanide in water and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in 1,2-dichloroethane. Either tetrabutylammonium (TBA{sup +}) or ClO{sub 4}{sup -} is chosen as the common ion in both phases to control the interfacial potential drop. The rate constant of heterogeneous ET reaction between TCNQ and ferrocyanide produced in-situ, k{sub 12}, is evaluated by SECM and is inversely proportional to the viscosity of the aqueous solution and directly proportional to the diffusion coefficient of K{sub 4}Fe(CN){sub 6} in water when the concentration of TCNQ in the DCE phase is in excess. The k{sub 12} dependence on viscosity is explained in terms of the longitudinal relaxation time of the solution. The rate constant of the heterogeneous ET reaction between TCNQ{sup -} and ferricyanide, k{sub 21}, is also obtained by SECM and these results cannot be explained by the same manner.

Interrelation of chemistry and process design in biodiesel manufacturing by heterogeneous catalysis

NARCIS (Netherlands)

Dimian, A.C.; Srokol, Z.W.; Mittelmeijer-Hazeleger, M.C.; Rothenberg, G.

2010-01-01

The pros and cons of using heterogeneous catalysis for biodiesel manufacturing are introduced, and explained from a chemistry and engineering viewpoint. Transesterification reactions of various feed types are then compared in batch and continuous process operation modes. The results show that the

Heterogeneous Risk Perceptions: The Case of Poultry Meat Purchase Intentions in Finland

Directory of Open Access Journals (Sweden)

Johanna Mäkelä

2013-10-01

Full Text Available This study focused on the heterogeneity of consumer reactions, measured through poultry meat purchase intentions, when facing three cases of risk. The heterogeneity was analysed by latent class logistic regression that included all three risk cases. Approximately 60% of the respondents belonged to the group of production risk avoiders, in which the intention to purchase risk food was significantly lower than in the second group of risk neutrals. In addition to socio-demographic variables, the purchase intentions were statistically associated with several attitude-based variables. We highlighted some policy implications of the heterogeneity. Overall, the study demonstrated that risk matters to consumers, not all risk is equal, and consumer types react somewhat differently to different types of risk.

Experimental study o the sodium-concrete reaction

International Nuclear Information System (INIS)

Goncalves, A.C.; Torres, A.R.; Brito Aghina, L.O. de; Messere e Castro, P.

1986-01-01

Effects and aspects of security are verified during a sodium leakage in high temperatures on liners of contention cells and directly on the concrete. As this kinetic process involves reactions between materials in solid state (such as oxides and carbonates) vapors and gases (such as water and CO 2 )) with liquid sodium, effects of each phase of the heterogeneous mixture are separately analysed. Are still analysed produced products and briefly discussed the kinetic of the sodium-concrete reaction. (Author) [pt

Heterogeneous catalysis in a micro channel using a layer of carbon nano fibers on the channel wall

NARCIS (Netherlands)

Loos, de S.R.A.; Schaaf, van der J.; Croon, de M.H.J.M.; Nijhuis, T.A.; Schouten, J.C.

2012-01-01

This paper presents the increase of the overall reaction rate of a heterogeneously catalyzed multi-phase reaction using a carbon nanofiber (CNF) based catalyst with a factor of 3.5–4 compared with an unsupported flat plate catalyst in a microreactor. This was done by quantifying the hydrogen

Nano-particulate Aluminium Nitride/Al: An Efficient and Versatile Heterogeneous Catalyst for the Synthesis of Biginelli Scaffolds

Science.gov (United States)

Tekale, S. U.; Tekale, A. B.; Kanhe, N. S.; Bhoraskar, S. V.; Pawar, R. P.

2011-12-01

Nano-particulate aluminium nitride/Al (7:1) is reported as a new heterogeneous solid acid catalyst for the synthesis of 3, 4-dihydroxypyrimidi-2-(1H)-ones and their sulphur analogues using the Biginelli reaction. This method involves short reaction time, easy separation, high yields and purity of products.

Heterogeneous chemical kinetics by modulated molecular beam mass spectrometry: limitations of technique

International Nuclear Information System (INIS)

Olander, D.R.

1977-01-01

The advantages and limitations of modulated molecular beam, mass spectrometry as applied to the study of heterogeneous chemical kinetics are reviewed. The process of deducing a model of the surface reaction from experimental data is illustrated by analysis of the hydrogen reduction of uranium dioxide

Identifying systematic DFT errors in catalytic reactions

DEFF Research Database (Denmark)

Christensen, Rune; Hansen, Heine Anton; Vegge, Tejs

2015-01-01

Using CO2 reduction reactions as examples, we present a widely applicable method for identifying the main source of errors in density functional theory (DFT) calculations. The method has broad applications for error correction in DFT calculations in general, as it relies on the dependence...... of the applied exchange–correlation functional on the reaction energies rather than on errors versus the experimental data. As a result, improved energy corrections can now be determined for both gas phase and adsorbed reaction species, particularly interesting within heterogeneous catalysis. We show...... that for the CO2 reduction reactions, the main source of error is associated with the C[double bond, length as m-dash]O bonds and not the typically energy corrected OCO backbone....

First derivative spectrophotometric determination of granisetron hydrochloride in presence of its hydrolytic products and preservative and application to pharmaceutical preparations.

Science.gov (United States)

Hewala, Ismail I; Bedair, Mona M; Shousha, Sherif M

2013-04-01

Granisetron is a selective 5-HT3 receptor antagonist used in prevention and treatment of chemotherapy-induced nausea and vomiting. The drug is available in tablet dosage form and parenteral dosage form containing benzyl alcohol as a preservative. The main route of degradation of granisetron is through hydrolysis. The present work describes the development of a simple, rapid, and reliable first derivative spectrophotometric method for the determination of granisetron in presence of its hydrolytic products as well as the formulations adjuvant and benzyl alcohol. The method is based on the measurement of the first derivative response of granisetron at 290 nm where the interference of the hydrolytic products, the co-formulated adjuvant and benzyl alcohol is completely eliminated. The proposed method was validated with respect to specificity, linearity, selectivity, accuracy, precision, robustness, detection, and quantification limits. Regression analysis showed good correlation between the first derivative response and the concentration of granisetron over a range of 8-16 μg ml(-1) . Statistical analysis proved the accuracy of the proposed method compared with a reference stability indicating high performance liquid chromatography method. The described method was successfully applied to the determination of granisetron in different batches of tablets and ampoules. The assay results obtained in this study strongly encourage us to apply the validated method for the quality control and routine analysis of tablets and parenteral preparations containing granisetron. Copyright © 2012 John Wiley & Sons, Ltd.

Quantitative phase analysis and microstructure characterization of magnetite nanocrystals obtained by microwave assisted non-hydrolytic sol–gel synthesis

Energy Technology Data Exchange (ETDEWEB)

Sciancalepore, Corrado, E-mail: corrado.sciancalepore@unimore.it [Department of Engineering “Enzo Ferrari”, University of Modena and Reggio Emilia, Via Pietro Vivarelli 10, 41100 Modena (Italy); Bondioli, Federica [Department of Industrial Engineering, University of Parma, Parco Area delle Scienze, 181/A, 43124 Parma (Italy); INSTM Consortium, Via G. Giusti 9, 51121 Firenze (Italy); Manfredini, Tiziano [Department of Engineering “Enzo Ferrari”, University of Modena and Reggio Emilia, Via Pietro Vivarelli 10, 41100 Modena (Italy); INSTM Consortium, Via G. Giusti 9, 51121 Firenze (Italy); Gualtieri, Alessandro [Department of Chemical and Geological Science, University of Modena and Reggio Emilia, Via S. Eufemia 19, 41121 Modena Italy (Italy)

2015-02-15

An innovative preparation procedure, based on microwave assisted non-hydrolytic sol–gel synthesis, to obtain spherical magnetite nanoparticles was reported together with a detailed quantitative phase analysis and microstructure characterization of the synthetic products. The nanoparticle growth was analyzed as a function of the synthesis time and was described in terms of crystallization degree employing the Rietveld method on the magnetic nanostructured system for the determination of the amorphous content using hematite as internal standard. Product crystallinity increases as the microwave thermal treatment is increased and reaches very high percentages for synthesis times longer than 1 h. Microstructural evolution of nanocrystals was followed by the integral breadth methods to obtain information on the crystallite size-strain distribution. The results of diffraction line profile analysis were compared with nanoparticle grain distribution estimated by dimensional analysis of the transmission electron microscopy (TEM) images. A variation both in the average grain size and in the distribution of the coherently diffraction domains is evidenced, allowing to suppose a relationship between the two quantities. The traditional integral breadth methods have proven to be valid for a rapid assessment of the diffraction line broadening effects in the above-mentioned nanostructured systems and the basic assumption for the correct use of these methods are discussed as well. - Highlights: • Fe{sub 3}O{sub 4} nanocrystals were obtained by MW-assisted non-hydrolytic sol–gel synthesis. • Quantitative phase analysis revealed that crystallinity up to 95% was reached. • The strategy of Rietveld refinements was discussed in details. • Dimensional analysis showed nanoparticles ranging from 4 to 8 nm. • Results of integral breadth methods were compared with microscopic analysis.

Quantitative phase analysis and microstructure characterization of magnetite nanocrystals obtained by microwave assisted non-hydrolytic sol–gel synthesis

International Nuclear Information System (INIS)

Sciancalepore, Corrado; Bondioli, Federica; Manfredini, Tiziano; Gualtieri, Alessandro

2015-01-01

An innovative preparation procedure, based on microwave assisted non-hydrolytic sol–gel synthesis, to obtain spherical magnetite nanoparticles was reported together with a detailed quantitative phase analysis and microstructure characterization of the synthetic products. The nanoparticle growth was analyzed as a function of the synthesis time and was described in terms of crystallization degree employing the Rietveld method on the magnetic nanostructured system for the determination of the amorphous content using hematite as internal standard. Product crystallinity increases as the microwave thermal treatment is increased and reaches very high percentages for synthesis times longer than 1 h. Microstructural evolution of nanocrystals was followed by the integral breadth methods to obtain information on the crystallite size-strain distribution. The results of diffraction line profile analysis were compared with nanoparticle grain distribution estimated by dimensional analysis of the transmission electron microscopy (TEM) images. A variation both in the average grain size and in the distribution of the coherently diffraction domains is evidenced, allowing to suppose a relationship between the two quantities. The traditional integral breadth methods have proven to be valid for a rapid assessment of the diffraction line broadening effects in the above-mentioned nanostructured systems and the basic assumption for the correct use of these methods are discussed as well. - Highlights: • Fe 3 O 4 nanocrystals were obtained by MW-assisted non-hydrolytic sol–gel synthesis. • Quantitative phase analysis revealed that crystallinity up to 95% was reached. • The strategy of Rietveld refinements was discussed in details. • Dimensional analysis showed nanoparticles ranging from 4 to 8 nm. • Results of integral breadth methods were compared with microscopic analysis

Homogenization technique for strongly heterogeneous zones in research reactors

International Nuclear Information System (INIS)

Lee, J.T.; Lee, B.H.; Cho, N.Z.; Oh, S.K.

1991-01-01

This paper reports on an iterative homogenization method using transport theory in a one-dimensional cylindrical cell model developed to improve the homogenized cross sections fro strongly heterogeneous zones in research reactors. The flux-weighting homogenized cross sections are modified by a correction factor, the cell flux ratio under an albedo boundary condition. The albedo at the cell boundary is iteratively determined to reflect the geometry effects of the material properties of the adjacent cells. This method has been tested with a simplified core model of the Korea Multipurpose Research Reactor. The results demonstrate that the reaction rates of an off-center control shroud cell, the multiplication factor, and the power distribution of the reactor core are close to those of the fine-mesh heterogeneous transport model

Coupled processes of fluid flow, solute transport, and geochemical reactions in reactive barriers

Energy Technology Data Exchange (ETDEWEB)

Kim, Jeongkon; Schwartz, Franklin W.; Xu, Tianfu; Choi, Heechul, and Kim, In S.

2004-01-02

A complex pattern of coupling between fluid flow and mass transport develops when heterogeneous reactions occur. For instance, dissolution and precipitation reactions can change a porous medium's physical properties, such as pore geometry and thus permeability. These changes influence fluid flow, which in turn impacts the composition of dissolved constituents and the solid phases, and the rate and direction of advective transport. Two-dimensional modeling studies using TOUGHREACT were conducted to investigate the coupling between flow and transport developed as a consequence of differences in density, dissolution precipitation, and medium heterogeneity. The model includes equilibrium reactions for aqueous species, kinetic reactions between the solid phases and aqueous constituents, and full coupling of porosity and permeability changes resulting from precipitation and dissolution reactions in porous media. In addition, a new permeability relationship is implemented in TOUGHREACT to examine the effects of geochemical reactions and density difference on plume migration in porous media. Generally, the evolutions in the concentrations of the aqueous phase are intimately related to the reaction-front dynamics. Plugging of the medium contributed to significant transients in patterns of flow and mass transport.

Aerobic oxidation of aqueous ethanol using heterogeneous gold catalysts: Efficient routes to acetic acid and ethyl acetate

DEFF Research Database (Denmark)

Jørgensen, Betina; Christiansen, Sofie Egholm; Thomsen, M.L.D.

2007-01-01

The aerobic oxidation of aqueous ethanol to produce acetic acid and ethyl acetate was studied using heterogeneous gold catalysts. Comparing the performance of Au/MgAl2O4 and Au/TiO2 showed that these two catalysts exhibited similar performance in the reaction. By proper selection of the reaction...

The study of biodiesel production using CaO as a heterogeneous catalytic reaction

Directory of Open Access Journals (Sweden)

Kamila Colombo

2017-06-01

Full Text Available With the aim of developing a process of biodiesel production that is environmentally benign much interest has been focused on the use of solid base catalysts, such as calcium oxide, for the transesterification of vegetable oils with methanol. In the study reported herein a recycling reactor was used in bench scale, with the capacity to produce 3 L of biodiesel. The reactor was designed especially for this research study. A full 23 factorial plan was used to evaluate the process parameters related to this study, in particular, the catalyst concentration, the alcohol to oil molar ratio and the reaction time. Using this equipment for the transesterification reaction resulted in the recovery of the excess alcohol. The reaction products were characterized using gas chromatography and liquid analysis to determine the ester and calcium concentrations, respectively. The main conclusions drawn were that the best conversion percentage (100% of biodiesel was reached when the methanol:oil molar ratio was 6:1, the reaction time was 75 min and the catalyst mass was 3% in relation to the oil mass used in this process. The CaO concentration determined exceeded the limit of concentration defined by legislation and thus a secondary operation was carried out to purify the reaction products obtained. The results of this study showed a high performance, and the proposed experiment could be used as a new and innovative way to produce biodiesel in the future.

Imine derivatives of lathonones. Part I -- Reactions of neodymium (III) isopropoxide with monofunctional bidendtate and bifunctional tridentate aldimines and ketamines

International Nuclear Information System (INIS)

Mital, S.P.; Singh, R.V.; Tandon, J.P.

1980-01-01

Nd(OPrsup(i))sub(2) (SB) and Nd(Oprsup(i))(SB)sub(2) [where SBH represents the molecule of monofunctional bidentate aldimine] type of derivatives have been synthesised by 1:1 and 1:2 molar reactions of neodymium isopropoxide with the aldimines having the donor system NOH and formed by the condensation of salicylaldehyde with alkylamines. However, bifunctional tridentate Schiff bases (LH) 2 have been found to yield Nd(OPrsup(i)) (L) and Nd 2 (L) 3 type of complexes in 1:1 and 2:3 molar ratio respectively. The isopropoxy groups of the 1:1 complexes have been found to undergo replacement reactions with excess of t-butanol and the resulting complexes are hydrolytically stable. All the newly synthesized complexes have been characterized on the basis of elemental analyses, molecular weight determinations, conductance measurements and infrared and proton magnetic resonance spectral studies. (auth.)

Constructing Bridges between Computational Tools in Heterogeneous and Homogeneous Catalysis

KAUST Repository

Falivene, Laura; Kozlov, Sergey M.; Cavallo, Luigi

2018-01-01

Better catalysts are needed to address numerous challenges faced by humanity. In this perspective, we review concepts and tools in theoretical and computational chemistry that can help to accelerate the rational design of homogeneous and heterogeneous catalysts. In particular, we focus on the following three topics: 1) identification of key intermediates and transition states in a reaction using the energetic span model, 2) disentanglement of factors influencing the relative stability of the key species using energy decomposition analysis and the activation strain model, and 3) discovery of new catalysts using volcano relationships. To facilitate wider use of these techniques across different areas, we illustrate their potentials and pitfalls when applied to the study of homogeneous and heterogeneous catalysts.

Constructing Bridges between Computational Tools in Heterogeneous and Homogeneous Catalysis

KAUST Repository

Falivene, Laura

2018-05-08

Better catalysts are needed to address numerous challenges faced by humanity. In this perspective, we review concepts and tools in theoretical and computational chemistry that can help to accelerate the rational design of homogeneous and heterogeneous catalysts. In particular, we focus on the following three topics: 1) identification of key intermediates and transition states in a reaction using the energetic span model, 2) disentanglement of factors influencing the relative stability of the key species using energy decomposition analysis and the activation strain model, and 3) discovery of new catalysts using volcano relationships. To facilitate wider use of these techniques across different areas, we illustrate their potentials and pitfalls when applied to the study of homogeneous and heterogeneous catalysts.

Use of length heterogeneity polymerase chain reaction (LH-PCR as non-invasive approach for dietary analysis of Svalbard reindeer, Rangifer tarandus platyrhynchus.

Directory of Open Access Journals (Sweden)

Sungbae Joo

Full Text Available To efficiently investigate the forage preference of Svalbard reindeer (Rangifer tarandus platyrhynchus, we applied length-heterogeneity polymerase chain reaction (LH-PCR based on length differences of internal transcribed spacer (ITS regions of ribosomal RNA (rRNA to fecal samples from R. tarandus platyrhynchus. A length-heterogeneity (LH database was constructed using both collected potential food sources of Svalbard reindeer and fecal samples, followed by PCR, cloning and sequencing. In total, eighteen fecal samples were collected between 2011 and 2012 from 2 geographic regions and 15 samples were successfully amplified by PCR. The LH-PCR analysis detected abundant peaks, 18.6 peaks on an average per sample, ranging from 100 to 500 bp in size and showing distinct patterns associated with both regions and years of sample collection. Principal component analysis (PCA resulted in clustering of 15 fecal samples into 3 groups by the year of collection and region with a statistically significant difference at 99.9% level. The first 2 principal components (PCs explained 71.1% of the total variation among the samples. Through comparison with LH database and identification by cloning and sequencing, lichens (Stereocaulon sp. and Ochrolechia sp. and plant species (Salix polaris and Saxifraga oppositifolia were detected as the food sources that contributed most to the Svalbard reindeer diet. Our results suggest that the use of LH-PCR analysis would be a non-invasive and efficient monitoring tool for characterizing the foraging strategy of Svalbard reindeer. Additionally, combining sequence information would increase its resolving power in identification of foraged diet components.

Large epidemic thresholds emerge in heterogeneous networks of heterogeneous nodes

Science.gov (United States)

Yang, Hui; Tang, Ming; Gross, Thilo

2015-08-01

One of the famous results of network science states that networks with heterogeneous connectivity are more susceptible to epidemic spreading than their more homogeneous counterparts. In particular, in networks of identical nodes it has been shown that network heterogeneity, i.e. a broad degree distribution, can lower the epidemic threshold at which epidemics can invade the system. Network heterogeneity can thus allow diseases with lower transmission probabilities to persist and spread. However, it has been pointed out that networks in which the properties of nodes are intrinsically heterogeneous can be very resilient to disease spreading. Heterogeneity in structure can enhance or diminish the resilience of networks with heterogeneous nodes, depending on the correlations between the topological and intrinsic properties. Here, we consider a plausible scenario where people have intrinsic differences in susceptibility and adapt their social network structure to the presence of the disease. We show that the resilience of networks with heterogeneous connectivity can surpass those of networks with homogeneous connectivity. For epidemiology, this implies that network heterogeneity should not be studied in isolation, it is instead the heterogeneity of infection risk that determines the likelihood of outbreaks.

Large epidemic thresholds emerge in heterogeneous networks of heterogeneous nodes.

Science.gov (United States)

Yang, Hui; Tang, Ming; Gross, Thilo

2015-08-21

One of the famous results of network science states that networks with heterogeneous connectivity are more susceptible to epidemic spreading than their more homogeneous counterparts. In particular, in networks of identical nodes it has been shown that network heterogeneity, i.e. a broad degree distribution, can lower the epidemic threshold at which epidemics can invade the system. Network heterogeneity can thus allow diseases with lower transmission probabilities to persist and spread. However, it has been pointed out that networks in which the properties of nodes are intrinsically heterogeneous can be very resilient to disease spreading. Heterogeneity in structure can enhance or diminish the resilience of networks with heterogeneous nodes, depending on the correlations between the topological and intrinsic properties. Here, we consider a plausible scenario where people have intrinsic differences in susceptibility and adapt their social network structure to the presence of the disease. We show that the resilience of networks with heterogeneous connectivity can surpass those of networks with homogeneous connectivity. For epidemiology, this implies that network heterogeneity should not be studied in isolation, it is instead the heterogeneity of infection risk that determines the likelihood of outbreaks.

Visualisation and characterisation of heterogeneous bimodal PDMS networks

DEFF Research Database (Denmark)

Bahrt, Frederikke; Daugaard, Anders Egede; Fleury, Clemence

2014-01-01

The existence of short-chain domains in heterogeneous bimodal PDMS networks has been confirmed visually, for the first time, through confocal fluorescence microscopy. The networks were prepared using a controlled reaction scheme where short PDMS chains were reacted below the gelation point...... bimodal networks with short-chain domains within a long-chain network. The average sizes of the short-chain domains were found to vary from 2.1 to 5.7 mm depending on the short-chain content. The visualised network structure could be correlated thereafter to the elastic properties, which were determined...... by rheology. All heterogeneous bimodal networks displayed significantly lower moduli than mono-modal PDMS elastomers prepared from the long polymer chains. Low-loss moduli as well as low-sol fractions indicate that low-elastic moduli can be obtained without compromising the network's structure...

Process Parameters Optimization of Potential SO42-/ZnO Acid Catalyst for Heterogeneous Transesterification of Vegetable Oil to Biodiesel

Directory of Open Access Journals (Sweden)

Istadi Istadi

2012-12-01

Full Text Available Among the possible renewable energy resources, diesel fuels derived from triglycerides of vegetable oils and animal fats have shown potential as substitutes for petroleum-based diesel fuels. The biodiesel could be produced from vegetable oils over homogeneous catalyst, heterogeneous catalyst, or enzymatic catalyst. In this study, the synthesized SO42-/ZnO catalyst was explored to be used in the heterogeneous biodiesel production by using the vegetable oils and methanol. The study began with the preparation of SO42-/ZnO catalyst followed by the transesterification reaction between vegetable oil with methanol. The independent variables (reaction time and the weight ratio of catalyst/oil were optimized to obtain the optimum biodiesel (fatty acid methyl ester yield. The results of this study showed that the acid catalyst SO42-/ZnO was potential to be used as catalyst for biodiesel production through heterogeneous transesterification of vegetable oils. Optimum operating condition for this catalytic reaction was the weight ratio of catalyst/oil of 8:1 and reaction time of 2.6 h with respect to 75.5% yield of methyl ester products. The biodiesel product was also characterized to identify the respected fatty acid methyl ester components. Copyright © 2012 by BCREC UNDIP. All rights reserved. (Selected Paper from International Conference on Chemical and Material Engineering (ICCME 2012Received: 23rd October 2012, Revised: 25th November 2012, Accepted: 25th November 2012[How to Cite: I. Istadi, Didi D. Anggoro, Luqman Buchori, Inshani Utami, Roikhatus Solikhah, (2012. Process Parameters Optimization of Potential SO42-/ZnO Acid Catalyst for Heterogeneous Transesterification of Vegetable Oil to Biodiesel. Bulletin of Chemical Reaction Engineering & Catalysis, 7(2: 150-157. (doi:10.9767/bcrec.7.2.4064.150-157][How to Link / DOI: http://dx.doi.org/10.9767/bcrec.7.2.4064.150-157 ] | View in 

Applications of fluorescence techniques to the study of uranium in homogeneous and heterogeneous environments: hydrolysis and photo-reduction reactions on titanium dioxide

International Nuclear Information System (INIS)

Eliet, Veronique

1996-01-01

This thesis describes the use of Time-Resolved Fluorescence to characterise the spectroscopy of hydroxo-complexes of hexavalent Uranium, and to study photochemical reactions involving these species at mineral/water interfaces. The instrumentation used comprised of either an excimer laser coupled to an optical multichannel analyser OMA or a Nd-YAG laser coupled to a stroboscopic photomultiplier. The hydrolysis of Uranium at a constant temperature of 25 deg. C, has been studied in the pH ranges 0-5 and 9-12. Deconvolution of spectra and fluorescence decay curves for Uranium yielded individual fluorescence spectra and decay times for uranyl UO 2 2+ and its hydroxo-complexes UO 2 OH + , (UO 2 )2(OH) 2 2+ , (UO 2 ) 3 (OH) 5 + et UO 2 (OH) 3 - . The comparison of fluorescence efficiencies for the various species showed that the complex (UO 2 )2(OH) 2 2+ is up to 85 times more fluorescent than uranyl, depending on the emission wavelength. Further, investigations of fluorescence decays as a function of temperature in the pH range 0-6, yielded activation energies for the various Uranium hydroxo species. The knowledge gained in homogeneous media served in the study of the photochemical behaviour of Uranium in suspensions of the semi-conductor mineral, TiO 2 . After UV-light absorption, charge carriers formed at the mineral surface were found to reduce hexavalent Uranium to the tetravalent oxidation state. Time-Resolved Fluorescence Spectroscopy has been used to monitor the kinetics of the oxidation state change. A reaction mechanism is proposed on the basis of results obtained by studying the kinetics of the process at different values of pH The role of humic substances on the heterogeneous redox reaction has also been examined. (author) [fr

Preparation of Mn(III)-Porphyrin-Immobilized Fe{sub 3}O{sub 4}@SiO{sub 2} Mesoparticles and Their Use in Heterogeneous Catalysis of Styrene Epoxidation

Energy Technology Data Exchange (ETDEWEB)

Kim, Jun Yeol; Lee, Kyung Yeon; Kim, Sun Dol; Lee, Suk Joong [Dept. of Chemistry, Research Institute for Natural Sciences, Korea University, Seoul (Korea, Republic of)

2015-07-15

They show high stability over their homogeneous counterparts. However, traditional heterogeneous catalysts tend to be less selective for fine chemical synthesis because they usually require high operation temperature and have the nonuniformity of active sites. To overcome these problems, an emerging strategy for preparing heterogeneous catalytic systems with better selectivity and milder reaction condition comprises the immobilization of homogeneous catalysts on organic polymers and inorganic supports. We have designed and synthesized novel Mn(III)-porphyrin-immobilized core-shell magnetic mesoparticles that heterogeneously catalyze styrene to styrene oxide with remarkably high activity compared with its homogeneous counterpart. These magnetic heterogeneous catalysts can be readily separated from the reaction mixture by magnetic manipulation and used for subsequent reactions multiple times without dramatic loss of activity. This immobilization of catalysts on magnetic supports promises a great potential toward the development of new class of oxidation catalysts, and the modification of catalysts to extend their lifetime is in progress.

Biodiesel Production using Heterogeneous Catalyst in CSTR: Sensitivity Analysis and Optimization

Science.gov (United States)

Keong, L. S.; Patle, D. S.; Shukor, S. R.; Ahmad, Z.

2016-03-01

Biodiesel as a renewable fuel has emerged as a potential replacement for petroleum-based diesels. Heterogeneous catalyst has become the focus of researches in biodiesel production with the intention to overcome problems associated with homogeneous catalyzed processes. The simulation of heterogeneous catalyzed biodiesel production has not been thoroughly studied. Hence, a simulation of carbon-based solid acid catalyzed biodiesel production from waste oil with high FFA content (50 weight%) was developed in the present work to study the feasibility and potential of the simulated process. The simulated process produces biodiesel through simultaneous transesterification and esterification with the consideration of reaction kinetics. The developed simulation is feasible and capable to produce 2.81kmol/hr of FAME meeting the international standard (EN 14214). Yields of 68.61% and 97.19% are achieved for transesterification and esterification respectively. Sensitivity analyses of FFA composition in waste oil, methanol to oil ratio, reactor pressure and temperature towards FAME yield from both reactions were carried out. Optimization of reactor temperature was done to maximize FAME products.

Biodiesel Production using Heterogeneous Catalyst in CSTR: Sensitivity Analysis and Optimization

International Nuclear Information System (INIS)

Keong, L S; Shukor, S R; Ahmad, Z; Patle, D S

2016-01-01

Biodiesel as a renewable fuel has emerged as a potential replacement for petroleum-based diesels. Heterogeneous catalyst has become the focus of researches in biodiesel production with the intention to overcome problems associated with homogeneous catalyzed processes. The simulation of heterogeneous catalyzed biodiesel production has not been thoroughly studied. Hence, a simulation of carbon-based solid acid catalyzed biodiesel production from waste oil with high FFA content (50 weight%) was developed in the present work to study the feasibility and potential of the simulated process. The simulated process produces biodiesel through simultaneous transesterification and esterification with the consideration of reaction kinetics. The developed simulation is feasible and capable to produce 2.81 kmol/hr of FAME meeting the international standard (EN 14214). Yields of 68.61% and 97.19% are achieved for transesterification and esterification respectively. Sensitivity analyses of FFA composition in waste oil, methanol to oil ratio, reactor pressure and temperature towards FAME yield from both reactions were carried out. Optimization of reactor temperature was done to maximize FAME products. (paper)

Exchange Reactions. Proceedings of the Symposium on Exchange Reactions

International Nuclear Information System (INIS)

1965-01-01

The mechanisms and kinetics of chemical reactions are of great interest to chemists. The study of exchange reactions in particular helps to shed light on the dynamics of chemical change, providing an insight into the structures and the reactivities of the chemical species involved. The main theme of this meeting was the subject of oxidation-reduction reactions in which the net result is the transfer of one or more electrons between the different oxidation states of the same element. Other studies reported included the transfer of protons, atoms, complex ligands or organic radicals between molecules. Heterogeneous exchange, which is of importance in many cases of catalytic action, was also considered. For a long time isotopic tracers have formed the most convenient means of studying exchange reactions and today a considerable amount of work continues to be done with their aid. Consequently, several papers presented at this Symposium reported on work carried out by purely radiochemical tracer methods. In recognition, however, of the important role which nuclear magnetic resonance and electron spin resonance play in this field, in particular in the study of fast reactions, a number of reports on investigations in which these techniques had been used was included in the programme. By kind invitation of the United States Government the Symposium on Exchange Reactions was held from 31 May to 4 June at the Brookhaven National Laboratory, Upton, Long Island, N.Y., USA. It was attended by 46 participants from nine countries and one inter-governmental organization. The publication of these Proceedings makes the contents of the papers and the discussion available to a wider audience

Abbott prism: a multichannel heterogeneous chemiluminescence immunoassay analyzer.

Science.gov (United States)

Khalil, O S; Zurek, T F; Tryba, J; Hanna, C F; Hollar, R; Pepe, C; Genger, K; Brentz, C; Murphy, B; Abunimeh, N

1991-09-01

We describe a multichannel heterogeneous immunoassay analyzer in which a sample is split between disposable reaction trays in a group of linear tracks. The system's pipettor uses noninvasive sensing of the sample volume and disposable pipet tips. Each assay track has (a) a conveyor belt for moving reaction trays to predetermined functional stations, (b) temperature-controlled tunnels, (c) noncontact transfer of the reaction mixture between incubation and detection wells, and (d) single-photon counting to detect a chemiluminescence (CL) signal from the captured immunochemical product. A novel disposable reaction tray, with separate reaction and detection wells and self-contained fluid removal, is used in conjunction with the transfer device on the track to produce a carryover-free system. The linear immunoassay track has nine predetermined positions for performing individual assay steps. Assay step sequence and timing is selected by changing the location of the assay modules between these predetermined positions. The assay methodology, a combination of microparticle capture and direct detection of a CL signal on a porous matrix, offers excellent sensitivity, specificity, and ease of automation. Immunoassay configurations have been tested for hepatitis B surface antigen and for antibodies to hepatitis B core antigen, hepatitis C virus, human immunodeficiency virus I and II, and human T-cell leukemia virus I and II.

Features of the kinetics of heterogeneous reactions with phase transformations on catalyst surfaces

Energy Technology Data Exchange (ETDEWEB)

Berman, A D; Krylov, O V

1978-01-01

This paper presents a review of 41 bibliographic references to experiments on the adsorption of various gases (e.g., carbon monoxide, formic acid, ammonia, and oxygen) on metals (e.g., nickel, molybdenum, and platinum) and oxides covers observations of two-dimensional phases during adsorption; the kinetics of adsorption and catalysis associated with two-dimensional phase transitions; and several approximate models for describing the kinetics of heterogeneous catalysis which account for two-dimensional phase transformations on catalyst surfaces.

Ozone initiated reactions and human comfort in indoor environments

DEFF Research Database (Denmark)

Tamas, Gyöngyi

2006-01-01

Chemical reactions between ozone and pollutants commonly found indoors have been suggested to cause adverse health and comfort effects among building occupants. Of special interest are reactions with terpenes and other pollutants containing unsaturated carbon-carbon bonds that are fast enough...... to occur under normal conditions in various indoor settings. These reactions are known to occur both in the gas phase (homogeneous reactions) and on the surfaces of building materials (heterogeneous reactions), producing a number of compounds that can be orders of magnitude more odorous and irritating than...... their precursors. The present thesis investigates the effects of ozone-initiated reactions with limonene and with various interior surfaces, including those associated with people, on short-term sensory responses. The evaluations were conducted using a perceived air quality (PAQ) method introduced by Fanger (1988...

Synthesis, Properties, and In Vitro Hydrolytic Degradation of Poly(d,l-lactide-co-glycolide-co-ε-caprolactone

Directory of Open Access Journals (Sweden)

Yixiu Liu

2016-01-01

Full Text Available Random copolymers of poly(d,l-lactide-co-glycolide-co-ε-caprolactone (PLGC were synthesized by the ring-opening polymerization of d,l-lactide (DLLA, glycolide (GA, and ε-caprolactone (CL. The effects of CL on the copolymers were evaluated to prepare suitable copolymers with controlled properties. Our results showed that the CL content significantly influenced the thermal and mechanical properties of the copolymers and that the CL content in compositions could be altered to control properties of random copolymers. The in vitro hydrolytic degradation of the resulting implants showed that the degradation rate of PLGC was lower than that of PLGA, which could markedly reduce acidic degradation products. Finally, we demonstrated that higher CL contents in compositions slowed degradation rates.

Heterogeneous OH oxidation of motor oil particles causes selective depletion of branched and less cyclic hydrocarbons.

Science.gov (United States)

Isaacman, Gabriel; Chan, Arthur W H; Nah, Theodora; Worton, David R; Ruehl, Chris R; Wilson, Kevin R; Goldstein, Allen H

2012-10-02

Motor oil serves as a useful model system for atmospheric oxidation of hydrocarbon mixtures typical of anthropogenic atmospheric particulate matter, but its complexity often prevents comprehensive chemical speciation. In this work we fully characterize this formerly "unresolved complex mixture" at the molecular level using recently developed soft ionization gas chromatography techniques. Nucleated motor oil particles are oxidized in a flow tube reactor to investigate the relative reaction rates of observed hydrocarbon classes: alkanes, cycloalkanes, bicycloalkanes, tricycloalkanes, and steranes. Oxidation of hydrocarbons in a complex aerosol is found to be efficient, with approximately three-quarters (0.72 ± 0.06) of OH collisions yielding a reaction. Reaction rates of individual hydrocarbons are structurally dependent: compared to normal alkanes, reaction rates increased by 20-50% with branching, while rates decreased ∼20% per nonaromatic ring present. These differences in rates are expected to alter particle composition as a function of oxidation, with depletion of branched and enrichment of cyclic hydrocarbons. Due to this expected shift toward ring-opening reactions heterogeneous oxidation of the unreacted hydrocarbon mixture is less likely to proceed through fragmentation pathways in more oxidized particles. Based on the observed oxidation-induced changes in composition, isomer-resolved analysis has potential utility for determining the photochemical age of atmospheric particulate matter with respect to heterogeneous oxidation.

Preparation and characterization of LTA-type zeolite framework dispersed ruthenium nanoparticles and their catalytic application in the hydrolytic dehydrogenation of ammonia–borane for efficient hydrogen generation

International Nuclear Information System (INIS)

Zahmakiran, Mehmet

2012-01-01

Highlights: ► Ru(0)NPs-ZK-4 were prepared and characterized by advanced analytical techniques. ► They achieve the hydrolysis of ammonia-borane with TOF = 5410 h −1 and TTO = 36700. ► They maintain 85% of their activity even at the fifth catalytic run. - Abstract: The safe and efficient hydrogen storage and production are major obstacles to use hydrogen as an energy carrier. Therefore, significant efforts have been focused on the development of new materials for the chemical hydrogen storage and production. Of particular importance, ammonia–borane (NH 3 BH 3 ) is emerging as one of the most promising solid hydrogen carrier due to its high gravimetric hydrogen storage capacity (19.6 wt.%) and low molecular weight (30.8 g/mol). ammonia–borane can release hydrogen gas upon catalytic hydrolysis under mild conditions. Herein, the discovery of a new catalytic material, ruthenium nanoparticles stabilized by ZK-4 zeolite framework, for this important reaction has been reported. This new catalyst system was prepared by borohydride reduction of ruthenium(III)-exchanged ZK-4 zeolite in water at room temperature. The characterization of the resulting material by advanced analytical tools shows the formation of ZK-4 zeolite dispersed ruthenium nanoparticles (2.9 ± 0.9 nm). The catalytic performance of the resulting supported ruthenium nanoparticles depending on activity, lifetime and reusability was demonstrated in the hydrolytic dehydrogenation of ammonia–borane. They were found to be highly active (initial TOF = 5410 h −1 ), long-lived (TTO = 36,700) and reusable catalyst (retaining of >85% of initial activity in the 5th reuse) in this important catalytic reaction at room temperature under air.

Heterogeneous Oxidation of Atmospheric Organic Aerosol: Kinetics of Changes to the Amount and Oxidation State of Particle-Phase Organic Carbon.

Science.gov (United States)

Kroll, Jesse H; Lim, Christopher Y; Kessler, Sean H; Wilson, Kevin R

2015-11-05

Atmospheric oxidation reactions are known to affect the chemical composition of organic aerosol (OA) particles over timescales of several days, but the details of such oxidative aging reactions are poorly understood. In this study we examine the rates and products of a key class of aging reaction, the heterogeneous oxidation of particle-phase organic species by the gas-phase hydroxyl radical (OH). We compile and reanalyze a number of previous studies from our laboratories involving the oxidation of single-component organic particles. All kinetic and product data are described on a common basis, enabling a straightforward comparison among different chemical systems and experimental conditions. Oxidation chemistry is described in terms of changes to key ensemble properties of the OA, rather than to its detailed molecular composition, focusing on two quantities in particular, the amount and the oxidation state of the particle-phase carbon. Heterogeneous oxidation increases the oxidation state of particulate carbon, with the rate of increase determined by the detailed chemical mechanism. At the same time, the amount of particle-phase carbon decreases with oxidation, due to fragmentation (C-C scission) reactions that form small, volatile products that escape to the gas phase. In contrast to the oxidation state increase, the rate of carbon loss is nearly uniform among most systems studied. Extrapolation of these results to atmospheric conditions indicates that heterogeneous oxidation can have a substantial effect on the amount and composition of atmospheric OA over timescales of several days, a prediction that is broadly in line with available measurements of OA evolution over such long timescales. In particular, 3-13% of particle-phase carbon is lost to the gas phase after one week of heterogeneous oxidation. Our results indicate that oxidative aging represents an important sink for particulate organic carbon, and more generally that fragmentation reactions play a major

Catchment heterogeneity controls emergent archetype concentration-discharge relationships

Science.gov (United States)

Musolff, A.; Fleckenstein, J. H.; Rao, P. S.; Jawitz, J. W.

2017-12-01

Relationships between in-stream dissolved solute concentrations (C) and discharge (Q) are often-used indicators of catchment-scale processes and their interference with human activities. Here we analyze observational C-Q relationships from 61 catchments and 8 different solutes across a wide range of land-uses and discharge regimes. This analysis is combined with a parsimonious stochastic modeling approach to test how C-Q relationships arise from spatial heterogeneity in catchment solute sources coupled with different timescales of biogeochemical reactions. The observational data exhibit archetypical dilution, enrichment, and constant C-Q patterns. Moreover, with land-use intensification we find decreasing C variability relative to Q variability (chemostatic export regime). Our model indicates that the dominant driver of emergent C-Q patterns was structured heterogeneity of solute sources implemented as correlation of source concentration to travel time. Regardless of the C-Q pattern, with decreasing source heterogeneity we consistently find lower variability in C than in Q and a dominance of chemostatic export regimes. Here, the variance in exported loads is determined primarily by variance of Q. We conclude that efforts to improve stream water quality and ecological integrity in intensely managed catchments should lead away from landscape homogenization by introducing structured source heterogeneity. References: Musolff, A., J. H. Fleckenstein, P. S. C. Rao, and J. W. Jawitz (2017), Emergent archetype patterns of coupled hydrologic and biogeochemical responses in catchments, Geophys. Res. Lett., 44(9), 4143-4151, doi: 10.1002/2017GL072630.

Solar fuels generation and molecular systems: is it homogeneous or heterogeneous catalysis?

Science.gov (United States)

Artero, Vincent; Fontecave, Marc

2013-03-21

Catalysis is a key enabling technology for solar fuel generation. A number of catalytic systems, either molecular/homogeneous or solid/heterogeneous, have been developed during the last few decades for both the reductive and oxidative multi-electron reactions required for fuel production from water or CO(2) as renewable raw materials. While allowing for a fine tuning of the catalytic properties through ligand design, molecular approaches are frequently criticized because of the inherent fragility of the resulting catalysts, when exposed to extreme redox potentials. In a number of cases, it has been clearly established that the true catalytic species is heterogeneous in nature, arising from the transformation of the initial molecular species, which should rather be considered as a pre-catalyst. Whether such a situation is general or not is a matter of debate in the community. In this review, covering water oxidation and reduction catalysts, involving noble and non-noble metal ions, we limit our discussion to the cases in which this issue has been directly and properly addressed as well as those requiring more confirmation. The methodologies proposed for discriminating homogeneous and heterogeneous catalysis are inspired in part by those previously discussed by Finke in the case of homogeneous hydrogenation reaction in organometallic chemistry [J. A. Widegren and R. G. Finke, J. Mol. Catal. A, 2003, 198, 317-341].

Two-Dimensional Resonance Raman Signatures of Vibronic Coherence Transfer in Chemical Reactions.

Science.gov (United States)

Guo, Zhenkun; Molesky, Brian P; Cheshire, Thomas P; Moran, Andrew M

2017-11-02

Two-dimensional resonance Raman (2DRR) spectroscopy has been developed for studies of photochemical reaction mechanisms and structural heterogeneity in condensed phase systems. 2DRR spectroscopy is motivated by knowledge of non-equilibrium effects that cannot be detected with traditional resonance Raman spectroscopy. For example, 2DRR spectra may reveal correlated distributions of reactant and product geometries in systems that undergo chemical reactions on the femtosecond time scale. Structural heterogeneity in an ensemble may also be reflected in the 2D spectroscopic line shapes of both reactive and non-reactive systems. In this chapter, these capabilities of 2DRR spectroscopy are discussed in the context of recent applications to the photodissociation reactions of triiodide. We show that signatures of "vibronic coherence transfer" in the photodissociation process can be targeted with particular 2DRR pulse sequences. Key differences between the signal generation mechanisms for 2DRR and off-resonant 2D Raman spectroscopy techniques are also addressed. Overall, recent experimental developments and applications of the 2DRR method suggest that it will be a valuable tool for elucidating ultrafast chemical reaction mechanisms.

Evaluated kinetic and photochemical data for atmospheric chemistry: Volume V – heterogeneous reactions on solid substrates

Directory of Open Access Journals (Sweden)

J. N. Crowley

2010-09-01

Full Text Available This article, the fifth in the ACP journal series, presents data evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the heterogeneous processes on surfaces of solid particles present in the atmosphere, for which uptake coefficients and adsorption parameters have been presented on the IUPAC website in 2010. The article consists of an introduction and guide to the evaluation, giving a unifying framework for parameterisation of atmospheric heterogeneous processes. We provide summary sheets containing the recommended uptake parameters for the evaluated processes. Four substantial appendices contain detailed data sheets for each process considered for ice, mineral dust, sulfuric acid hydrate and nitric acid hydrate surfaces, which provide information upon which the recommendations are made.

Selective Hydrodeoxygenation of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran over Heterogeneous Iron Catalysts.

Science.gov (United States)

Li, Jiang; Liu, Jun-Ling; Liu, He-Yang; Xu, Guang-Yue; Zhang, Jun-Jie; Liu, Jia-Xing; Zhou, Guang-Lin; Li, Qin; Xu, Zhi-Hao; Fu, Yao

2017-04-10

This work provided the first example of selective hydrodeoxygenation of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) over heterogeneous Fe catalysts. A catalyst prepared by the pyrolysis of an Fe-phenanthroline complex on activated carbon at 800 °C was demonstrated to be the most active heterogeneous Fe catalyst. Under the optimal reaction conditions, complete conversion of HMF was achieved with 86.2 % selectivity to DMF. The reaction pathway was investigated thoroughly, and the hydrogenation of the C=O bond in HMF was demonstrated to be the rate-determining step during the hydrodeoxygenation, which could be accelerated greatly by using alcohol solvents as additional H-donors. The excellent stability of the Fe catalyst, which was probably a result of the well-preserved active species and the pore structure of the Fe catalyst in the presence of H 2 , was demonstrated in batch and continuous flow fixed-bed reactors. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemical Reactions Catalyzed by Metalloporphyrin-Based Metal-Organic Frameworks

Directory of Open Access Journals (Sweden)

Kelly Aparecida Dias de Freitas Castro

2013-06-01

Full Text Available The synthetic versatility and the potential application of metalloporphyrins (MP in different fields have aroused researchers’ interest in studying these complexes, in an attempt to mimic biological systems such as cytochrome P-450. Over the last 40 years, synthetic MPs have been mainly used as catalysts for homogeneous or heterogeneous chemical reactions. To employ them in heterogeneous catalysis, chemists have prepared new MP-based solids by immobilizing MP onto rigid inorganic supports, a strategy that affords hybrid inorganic-organic materials. More recently, materials obtained by supramolecular assembly processes and containing MPs as building blocks have been applied in a variety of areas, like gas storage, photonic devices, separation, molecular sensing, magnets, and heterogeneous catalysis, among others. These coordination polymers, known as metal-organic frameworks (MOFs, contain organic ligands or complexes connected by metal ions or clusters, which give rise to a 1-, 2- or 3-D network. These kinds of materials presents large surface areas, Brønsted or redox sites, and high porosity, all of which are desirable features in catalysts with potential use in heterogeneous phases. Building MOFs based on MP is a good way to obtain solid catalysts that offer the advantages of bioinspired systems and zeolitic materials. In this mini review, we will adopt a historical approach to present the most relevant MP-based MOFs applicable to catalytic reactions such as oxidation, reduction, insertion of functional groups, and exchange of organic functions.

Asymmetric C-C Bond-Formation Reaction with Pd: How to Favor Heterogeneous or Homogeneous Catalysis?

DEFF Research Database (Denmark)

Reimann, S.; Grunwaldt, Jan-Dierk; Mallat, T.

2010-01-01

The enantioselective allylic alkylation of (E)-1,3-diphenylallyl acetate was studied to clarify the heterogeneous or homogeneous character of the Pd/Al2O3-(R)-BINAP catalyst system. A combined approach was applied: the catalytic tests were completed with in situ XANES measurements to follow...

: Recyclable, ligand free palladium(II) catalyst for Heck reaction

Indian Academy of Sciences (India)

well as heterogeneous palladium catalysts, generated from either palladium(0) compounds or palladium(II) acetate or chloride salts.6 Several ligands such as phosphines, phoshites, carbenes, thioethers have been successfully employed for this reaction.7 However, homogeneous catalysis results in problems of recovery.

Heterogeneous reaction of HO2 with airborne TiO2 particles and its implication for climate change mitigation strategies

Science.gov (United States)

Moon, Daniel R.; Taverna, Giorgio S.; Anduix-Canto, Clara; Ingham, Trevor; Chipperfield, Martyn P.; Seakins, Paul W.; Baeza-Romero, Maria-Teresa; Heard, Dwayne E.

2018-01-01

One geoengineering mitigation strategy for global temperature rises resulting from the increased concentrations of greenhouse gases is to inject particles into the stratosphere to scatter solar radiation back to space, with TiO2 particles emerging as a possible candidate. Uptake coefficients of HO2, γ(HO2), onto sub-micrometre TiO2 particles were measured at room temperature and different relative humidities (RHs) using an atmospheric pressure aerosol flow tube coupled to a sensitive HO2 detector. Values of γ(HO2) increased from 0.021 ± 0.001 to 0.036 ± 0.007 as the RH was increased from 11 to 66 %, and the increase in γ(HO2) correlated with the number of monolayers of water surrounding the TiO2 particles. The impact of the uptake of HO2 onto TiO2 particles on stratospheric concentrations of HO2 and O3 was simulated using the TOMCAT three-dimensional chemical transport model. The model showed that, when injecting the amount of TiO2 required to achieve the same cooling effect as the Mt Pinatubo eruption, heterogeneous reactions between HO2 and TiO2 would have a negligible effect on stratospheric concentrations of HO2 and O3.

Bacterial synergism in lignocellulose biomass degradation : Complementary roles of degraders as influenced by complexity of the carbon source

NARCIS (Netherlands)

Cortes Tolalpa, Larisa; Falcao Salles, Joana; van Elsas, Jan

2017-01-01

Lignocellulosic biomass (LCB) is an attractive source of carbon for the production of sugars and other chemicals. Due to its inherent complexity and heterogeneity, efficient biodegradation requires the actions of different types of hydrolytic enzymes. In nature, complex microbial communities that

Phase behavior and reactive transport of partial melt in heterogeneous mantle model

Science.gov (United States)

Jordan, J.; Hesse, M. A.

2013-12-01

The reactive transport of partial melt is the key process that leads to the chemical and physical differentiation of terrestrial planets and smaller celestial bodies. The essential role of the lithological heterogeneities during partial melting of the mantle is increasingly recognized. How far can enriched melts propagate while interacting with the ambient mantle? Can the melt flow emanating from a fertile heterogeneity be localized through a reactive infiltration feedback in a model without exogenous factors or contrived initial conditions? A full understanding of the role of heterogeneities requires reactive melt transport models that account for the phase behavior of major elements. Previous work on reactive transport in the mantle focuses on trace element partitioning; we present the first nonlinear chromatographic analysis of reactive melt transport in systems with binary solid solution. Our analysis shows that reactive melt transport in systems with binary solid solution leads to the formation of two separate reaction fronts: a slow melting/freezing front along which enthalpy change is dominant and a fast dissolution/precipitation front along which compositional changes are dominated by an ion-exchange process over enthalpy change. An intermediate state forms between these two fronts with a bulk-rock composition and enthalpy that are not necessarily bounded by the bulk-rock composition and enthalpy of either the enriched heterogeneity or the depleted ambient mantle. The formation of this intermediate state makes it difficult to anticipate the porosity changes and hence the stability of reaction fronts. Therefore, we develop a graphical representation for the solution that allows identification of the intermediate state by inspection, for all possible bulk-rock compositions and enthalpies of the heterogeneity and the ambient mantle. We apply the analysis to the partial melting of an enriched heterogeneity. This leads to the formation of moving precipitation

Heterogeneous reactions and aerosol formation in flue gas cleaning by electron beam

International Nuclear Information System (INIS)

Baumann, W.; Jordan, S.; Leichsenring, C.H.; Maetzing, H.; Paur, H.R.; Schikarski, W.

1990-08-01

The electron beam dry scrubbing process is a simultaneous method for the removal of SO 2 and NO x from flue gas. By electron irradiation radicals (OH, O 2 H, O) are formed from the main flue gas components which oxidize NO x and SO 2 into the acids HNO 3 and H 2 SO 4 . These are then neutralized by the injection of NH 3 . A submicron aerosol consisting of ammonium salts is formed which is filtered from the offgas. The main pathways of the gas phase chemistry and product formation have been elucidated by experimental and theoretical studies. Back reactions which occur in the gas and the particle phase limit the energy efficiency of the process. By recirculation of irradiated gas into the reaction vessel (multiple irradiation) a significant improvement of removal yields was obtained. This enhancement of the energy efficiency requires the removal of products between the irradiation steps. Studies show that the material balance is complete. Deficits in the N and S balance of the process are due to the additional formation of molecular nitrogen and the deposition of ammonium sulfate in the ducts. Aerosol formation participates only with 30% in the material balance. The remaining 70% of the product are formed by surface reactions in the filter cake (40%) and in the ducts (30%). (orig.) With 38 figs., 29 tabs [de

Synthesis of biodiesel from pongamia oil using heterogeneous ion-exchange resin catalyst.

Science.gov (United States)

Jaya, N; Selvan, B Karpanai; Vennison, S John

2015-11-01

Biodiesel is a clean-burning renewable substitute fuel for petroleum. Biodiesel could be effectively produced by transesterification reaction of triglycerides of vegetable oils with short-chain alcohols in the presence of homogeneous or heterogeneous catalysts. Conventionally, biodiesel manufacturing processes employ strong acids or bases as catalysts. But, separation of the catalyst and the by-product glycerol from the product ester is too expensive to justify the product use as an automobile fuel. Hence heterogeneous catalysts are preferred. In this study, transesterification of pongamia oil with ethanol was performed using a solid ion-exchange resin catalyst. It is a macro porous strongly basic anion exchange resin. The process parameters affecting the ethyl ester yield were investigated. The reaction conditions were optimized for the maximum yield of fatty acid ethyl ester (FAEE) of pongamia oil. The properties of FAEE were compared with accepted standards of biodiesel. Engine performance was also studied with pongamia oil diesel blend and engine emission characteristics were observed. Copyright © 2015 Elsevier Inc. All rights reserved.

Compositional evolution of particle-phase reaction products and water in the heterogeneous OH oxidation of model aqueous organic aerosols

Directory of Open Access Journals (Sweden)

M. M. Chim

2017-12-01

Full Text Available Organic compounds present at or near the surface of aqueous droplets can be efficiently oxidized by gas-phase OH radicals, which alter the molecular distribution of the reaction products within the droplet. A change in aerosol composition affects the hygroscopicity and leads to a concomitant response in the equilibrium amount of particle-phase water. The variation in the aerosol water content affects the aerosol size and physicochemical properties, which in turn governs the oxidation kinetics and chemistry. To attain better knowledge of the compositional evolution of aqueous organic droplets during oxidation, this work investigates the heterogeneous OH-radical-initiated oxidation of aqueous methylsuccinic acid (C5H8O4 droplets, a model compound for small branched dicarboxylic acids found in atmospheric aerosols, at a high relative humidity of 85 % through experimental and modeling approaches. Aerosol mass spectra measured by a soft atmospheric pressure ionization source (Direct Analysis in Real Time, DART coupled with a high-resolution mass spectrometer reveal two major products: a five carbon atom (C5 hydroxyl functionalization product (C5H8O5 and a C4 fragmentation product (C4H6O3. These two products likely originate from the formation and subsequent reactions (intermolecular hydrogen abstraction and carbon–carbon bond scission of tertiary alkoxy radicals resulting from the OH abstraction occurring at the methyl-substituted carbon site. Based on the identification of the reaction products, a kinetic model of oxidation (a two-product model coupled with the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients (AIOMFAC model is built to simulate the size and compositional changes of aqueous methylsuccinic acid droplets during oxidation. Model results show that at the maximum OH exposure, the droplets become slightly more hygroscopic after oxidation, as the mass fraction of water is predicted to increase from

A quenched-flow system for measuring heterogeneous enzyme kinetics with sub-second time resolution

DEFF Research Database (Denmark)

Olsen, Johan Pelck; Kari, Jeppe; Borch, Kim

2017-01-01

of insoluble substrate. Perhaps for this reason, transient kinetics has rarely been reported for heterogeneous enzyme reactions. Here, we describe a quenched-flow system using peristaltic pumps and stirred substrate suspensions with a dead time below 100 ms. The general performance was verified by alkali...

Synthesis of carbonate esters by carboxymethylation using NaAlO2 as a highly active heterogeneous catalyst

OpenAIRE

Ramesh, Sreerangappa; Indukuri, Kiran; Riant, Olivier; Debecker, Damien

2018-01-01

Sodium aluminate is presented as a highly active heterogeneous catalyst able to convert a range of alcohols into the corresponding mixed carbonate esters, in high yield and under green conditions. The reaction is carried out using dimethyl carbonate both as a reactant and solvent, at 90°C. Allylic, aliphatic and aromatic alcohols are converted in good yields. The solid catalyst is shown to be truly heterogeneous, resistant to leaching, and recyclable.

Highly Dispersed Pseudo-Homogeneous and Heterogeneous Catalysts Synthesized via Inverse Micelle Solutions for the Liquefaction of Coal

Energy Technology Data Exchange (ETDEWEB)

Hampden-Smith, M.; Kawola, J.S.; Martino, A.; Sault, A.G.; Yamanaka, S.A.

1999-01-05

The mission of this project was to use inverse micelle solutions to synthesize nanometer sized metal particles and test the particles as catalysts in the liquefaction of coal and other related reactions. The initial focus of the project was the synthesis of iron based materials in pseudo-homogeneous form. The frost three chapters discuss the synthesis, characterization, and catalyst testing in coal liquefaction and model coal liquefaction reactions of iron based pseudo-homogeneous materials. Later, we became interested in highly dispersed catalysts for coprocessing of coal and plastic waste. Bifunctional catalysts . to hydrogenate the coal and depolymerize the plastic waste are ideal. We began studying, based on our previously devised synthesis strategies, the synthesis of heterogeneous catalysts with a bifunctional nature. In chapter 4, we discuss the fundamental principles in heterogeneous catalysis synthesis with inverse micelle solutions. In chapter 5, we extend the synthesis of chapter 4 to practical systems and use the materials in catalyst testing. Finally in chapter 6, we return to iron and coal liquefaction now studied with the heterogeneous catalysts.

Isotopic exchange reaction between barium ion and tri barium phosphate

International Nuclear Information System (INIS)

Bilgin, G.B.; Cetin, I.

1982-01-01

Heterogeneous exchange reaction of tri barium phosphate in barium chloride solution has been studied using 133 Ba as a tracer. The results show that the exchange fraction increases as barium chloride concentration increases for different mole ratio of the exchange ion on the solid surface and in the solution. The phenomenon was studied with respect to the previous treatment of the precipitate leading to different crystal sizes and the effect of reaction time. (author)

Structure from Dynamics: Vibrational Dynamics of Interfacial Water as a Probe of Aqueous Heterogeneity

Science.gov (United States)

2018-01-01

The structural heterogeneity of water at various interfaces can be revealed by time-resolved sum-frequency generation spectroscopy. The vibrational dynamics of the O–H stretch vibration of interfacial water can reflect structural variations. Specifically, the vibrational lifetime is typically found to increase with increasing frequency of the O–H stretch vibration, which can report on the hydrogen-bonding heterogeneity of water. We compare and contrast vibrational dynamics of water in contact with various surfaces, including vapor, biomolecules, and solid interfaces. The results reveal that variations in the vibrational lifetime with vibrational frequency are very typical, and can frequently be accounted for by the bulk-like heterogeneous response of interfacial water. Specific interfaces exist, however, for which the behavior is less straightforward. These insights into the heterogeneity of interfacial water thus obtained contribute to a better understanding of complex phenomena taking place at aqueous interfaces, such as photocatalytic reactions and protein folding. PMID:29490138

New heterogeneous acid catalysts in the synthesis of biodiesel; Estudo de novos catalisadores heterogeneous acidos na sintese de biodiesel

Energy Technology Data Exchange (ETDEWEB)

Soldi, Rafael A.; Cesar-Oliveira, Maria Aparecida F. [Universidade Federal do Parana (UFPR), Curitiba, PR (Brazil). Dept. de Quimica. Lab. de Polimeros Sinteticos], e-mail: mafco@quimica.ufpr.br; Oliveira, Angelo R.S.; Ramos, Luiz P. [Universidade Federal do Parana (UFPR), Curitiba, PR (Brazil). Dept. de Quimica. Centro de Pesquisa em Quimica Aplicada (CEPESQ)

2007-07-01

In this work, sulfonated polystyrene compounds (PSS) were synthesized from linear polystyrene (PS). Several methods and experimental conditions were investigated for the sulfonation of PS, producing catalytically active polymeric materials with sulfonation degrees in the range of 5.0-6.2 mmol -SO{sub 3}H/g of dry polymer. The performance of these catalysts was evaluated in transesterification reactions of beef tallow and vegetable oils with ethanol and methanol. For the sake of comparison, the same reaction conditions employed for the PSS catalysts were also used for an Amberlyst 15 (3,7 mmol SO{sub 3}H/g - Aldrich). The PSS samples were shown to be insoluble in the reaction media, leading to conversion rates of 85%, 75% and 80% of the refined soybean oil, beef tallow and crude corn oil in to ethyl esters, respectively, and 94% of the refined soybean oil methyl esters. Amberlyst 15 was studied as an alternative to the process, but its conversion rate to alkyl esters was very low in the employed conditions. These results demonstrated that our synthetic PSS materials have a great potential to act as heterogeneous catalysts for transesterification. (author)

Clinical implications of heterogeneity of tumor response to radiation therapy

International Nuclear Information System (INIS)

Suit, H.; Skates, S.; Taghian, A.; Okunieff, P.; Efird, J.T.

1992-01-01

Heterogeneity of response of tumor tissue to radiation clearly exists. Major parameters include histopathologic type, size (number of tumor rescue units (TRUs)), hemoglobin concentration, cell proliferation kinetics and immune rejection reaction by host. Further, normal and presumably tumor tissue response is altered in certain genetic diseases, e.g. ataxia telangiectasia. Any assessment of response of tumor tissue to a new treatment method or the testing of a new clinical response predictor is optimally based upon a narrow strata, viz., uniform with respect to known parameters of response, e.g. size, histological type. Even among tumors of such a clinical defined narrow strata, there will be residual heterogeneity with respect to inherent cellular radiation sensitivity, distributions of pO 2 , (SH), cell proliferation, etc. (author). 39 refs., 7 figs., 3 tabs

Regio- and Enantioselective Sequential Dehalogenation of rac-1,3-Dibromobutane by Haloalkane Dehalogenase LinB.

Science.gov (United States)

Gross, Johannes; Prokop, Zbyněk; Janssen, Dick; Faber, Kurt; Hall, Mélanie

2016-08-03

The hydrolytic dehalogenation of rac-1,3-dibromobutane catalyzed by the haloalkane dehalogenase LinB from Sphingobium japonicum UT26 proceeds in a sequential fashion: initial formation of intermediate haloalcohols followed by a second hydrolytic step to produce the final diol. Detailed investigation of the course of the reaction revealed favored nucleophilic displacement of the sec-halogen in the first hydrolytic event with pronounced R enantioselectivity. The second hydrolysis step proceeded with a regioselectivity switch at the primary position, with preference for the S enantiomer. Because of complex competition between all eight possible reactions, intermediate haloalcohols formed with moderate to good ee ((S)-4-bromobutan-2-ol: up to 87 %). Similarly, (S)-butane-1,3-diol was formed at a maximum ee of 35 % before full hydrolysis furnished the racemic diol product. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Heterogeneity of hydrolytic enzyme activities under drought: imaging and quantitative analysis

Science.gov (United States)

Sanaullah, Muhammad; Razavi, Bahar S.; Kuzyakov, Yakov

2015-04-01

The zymography-based "snap-shoot" of enzyme activities in the rhizosphere is challenging to detect the in situ microbial response to global climate change. We developed in situ soil zymography and used it for identification and localization of hotspots of β-glucosidase activity in the rhizosphere of maize under drought stress (30% of field capacity). The zymographic signals were especially high at root tips and were much stronger for activity of β-glucosidase under drought as compared with optimal moisture (70% of field capacity). This distribution of enzyme activity was confirmed by fluorogenically labelled substrates applied directly to the root exudates. The activity of β-glucosidase in root exudates (produced by root and microorganism associated on the root surface), sampled within 1 hour after zymography was significantly higher by drought stressed plants as compared with optimal moisture. In contrast, the β-glucosidase activity in destructively sampled rhizosphere soil was lower under drought stress compared with optimal moisture. Furthermore, drought stress did not affected β-glucosidase activity in bulk soil, away from rhizosphere. Consequently, we conclude that higher release of mucilage by roots und drought stimulated β-glucosidase activity in the rhizosphere. Thus, the zymography revealed plant-mediated mechanisms accelerating β-glucosidase activity under drought at the root-soil interface. So, coupling of zymography and enzyme assays in the rhizosphere and non-rhizosphere soil enables precise mapping the changes in two-dimensional distribution of enzyme activities due to climate change within dynamic soil interfaces.

Synthesis of a molecularly defined single-active site heterogeneous catalyst for selective oxidation of N-heterocycles.

Science.gov (United States)

Zhang, Yujing; Pang, Shaofeng; Wei, Zhihong; Jiao, Haijun; Dai, Xingchao; Wang, Hongli; Shi, Feng

2018-04-13

Generally, a homogeneous catalyst exhibits good activity and defined active sites but it is difficult to recycle. Meanwhile, a heterogeneous catalyst can easily be reused but its active site is difficult to reveal. It is interesting to bridge the gap between homogeneous and heterogeneous catalysis via controllable construction of a heterogeneous catalyst containing defined active sites. Here, we report that a molecularly defined, single-active site heterogeneous catalyst has been designed and prepared via the oxidative polymerization of maleimide derivatives. These polymaleimide derivatives can be active catalysts for the selective oxidation of heterocyclic compounds to quinoline and indole via the recycling of -C=O and -C-OH groups, which was confirmed by tracing the reaction with GC-MS using maleimide as the catalyst and by FT-IR analysis with polymaleimide as the catalyst. These results might promote the development of heterogeneous catalysts with molecularly defined single active sites exhibiting a comparable activity to homogeneous catalysts.

Depressurization accident analysis of MPBR by PBRSIM with chemical reaction model

International Nuclear Information System (INIS)

No, Hee Cheon; Kadak, A. C.

2002-01-01

The simple model for natural circulation is implemented into PBR S IM to provide air inlet velocity from the containment air space. For the friction and form loss only the pebble region is considered conservatively modeling laminar flow through a packed bed. For the chemical reaction model of PBR S IM the oxidation rate is determined as the minimum value of three mechanisms estimated at each time step: oxygen mass flow rate entering the bottom of the reflector, oxidation rate by kinetics, and oxygen mass flow rate arriving at the graphite surface by diffusion. Oxygen mass flux arriving at the graphite surface by diffusion is estimated based on energy-mass analogy. Two types of exothermic chemical reaction are considered: (C + zO 2 → xCO + yCO 2 ) and (2CO + O 2 2CO 2 ). The heterogeneous and homogeneous chemical reaction rates by kinetics are determined by INEEL and Bruno correlations, respectively. The instantaneous depressurization accident of MPBR is simulated using PBR S IM with chemical model. The air inlet velocity is initially rapidly dropped within 10 hr and reaches a saturation value of about 1.5cm/s. The oxidation rate by the diffusion process becomes lower than that by the chemical kinetics above 600K. The maximum pebble bed temperatures without and with chemical reaction reach the peak values of 1560 and 1617 .deg. C at 80 hr and 92 hr, respectively. As the averaged temperatures in the bottom reflector and the pebble bed regions increase with time, (C+1/2O2 ->CO) reaction becomes dominant over (C+O 2 →CO 2 ) reaction. Also, the CO generated by (C+1/2O 2 →CO) reaction will be consumed by (2CO+O 2 →2CO 2 ) reaction and the energy homogeneously generated by this CO depletion reaction becomes dominant over the heterogeneous reaction

Amberlyst-15: An Efficient and reusable heterogeneous catalyst for the synthesis of β-amino carbonyl compounds

Directory of Open Access Journals (Sweden)

Pathakota Venkata Ramana

2015-12-01

Full Text Available A simple and efficient method has been developed for the synthesis of β-amino carbonyl compounds from aromatic ketones, aldehydes and amines by Mannich reaction in the presence of amberlyst-15 as a reusable heterogeneous catalyst at room temperature under solvent-free conditions. The noteworthy advantages of the present method are short reaction times, good product yields, simple procedures and use of non-toxic catalyst.

Catalytic and Gas-Solid Reactions Involving HCN over Limestone

DEFF Research Database (Denmark)

Jensen, Anker; Johnsson, Jan Erik; Dam-Johansen, Kim

1997-01-01

In coal-fired combustion systems solid calcium species may be present as ash components or limestone added to the combustion chamber. In this study heterogeneous reactions involving HCN over seven different limestones were investigated in a laboratory fixed-bed quartz reactor at 873-1,173 K...

A multifunctional microwave plasma reaction apparatus and its applications

International Nuclear Information System (INIS)

Wang Xizhang; Wu Qiang; Hu Zheng; Xu Hua; Miao Shui; Chen Yi

2000-01-01

A multifunctional apparatus for microwave plasma reaction has been set up, which can be used in the fields such as chemical synthesis, surface modification, and heterogeneous catalysis. The apparatus has laid an experimental foundation for new methods, new technologies, and new train of thoughts to be explored

Spatial heterogeneities within an individual catalyst particle during reaction as revealed by in-situ micro-spectroscopy

NARCIS (Netherlands)

Kox, M.H.F.

2009-01-01

Heterogeneous catalysts are solids, which are of fundamental importance in (petro-) chemical, pharmaceutical and environmental industries. The majority (> 85%) of all chemicals and transportation fuels have come into contact with at least one catalyst material during their manufacturing process. In

Crystallization and preliminary X-ray crystallographic study of the wild type and two mutants of the CP1 hydrolytic domain from Aquifex aeolicus leucyl-tRNA synthetase

Energy Technology Data Exchange (ETDEWEB)

Cura, Vincent; Olieric, Natacha; Guichard, Alexandre [Département de Biologie et Génomique Structurales, UMR 7104, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP Strasbourg, 1 Rue Laurent Fries, 67404 Illkirch (France); Wang, En-Duo [State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, The Chinese Academy of Sciences, 320 Yue Yang Road, Shanghai 200031 (China); Moras, Dino [Département de Biologie et Génomique Structurales, UMR 7104, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP Strasbourg, 1 Rue Laurent Fries, 67404 Illkirch (France); Eriani, Gilbert [Architecture et Réactivité de l’ARN, UPR 9002, Institut de Biologie Moléculaire et Cellulaire du CNRS, 15 Rue René Descartes, 67084 Strasbourg (France); Cavarelli, Jean, E-mail: cava@igbmc.u-strasbg.fr [Département de Biologie et Génomique Structurales, UMR 7104, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP Strasbourg, 1 Rue Laurent Fries, 67404 Illkirch (France)

2005-10-01

The wild-type editing CP1 domain of A. aeolicus leucyl-tRNA synthetase and two mutant CP1 domains have been overexpressed, purified and crystallized. X-ray diffraction data have been collected to 1.8 Å, which has enabled determination of the structures by molecular replacement. The editing or hydrolytic CP1 domain of leucyl-tRNA synthetase (LeuRS) hydrolyses several misactivated amino acids. The CP1 domain of Aquifex aeolicus LeuRS was expressed, purified and crystallized by the hanging-drop vapour-diffusion method using ammonium sulfate as precipitant. Crystals belong to space group P2{sub 1}2{sub 1}2{sub 1}, with unit-cell parameters a = 38.8, b = 98.4, c = 116.7 Å. Crystals diffract to beyond 1.8 Å resolution and contain two monomers in the asymmetric unit. Two CP1 mutants in which a conserved threonine residue essential for the fidelity of the hydrolytic pathway is mutated to alanine or glutamic acid have also been expressed and crystallized. Crystals of the two CP1 mutants are isomorphs of the wild type and diffract to beyond 1.9 Å resolution. All structures were solved by molecular-replacement techniques.

Crystallization and preliminary X-ray crystallographic study of the wild type and two mutants of the CP1 hydrolytic domain from Aquifex aeolicus leucyl-tRNA synthetase

International Nuclear Information System (INIS)

Cura, Vincent; Olieric, Natacha; Guichard, Alexandre; Wang, En-Duo; Moras, Dino; Eriani, Gilbert; Cavarelli, Jean

2005-01-01

The wild-type editing CP1 domain of A. aeolicus leucyl-tRNA synthetase and two mutant CP1 domains have been overexpressed, purified and crystallized. X-ray diffraction data have been collected to 1.8 Å, which has enabled determination of the structures by molecular replacement. The editing or hydrolytic CP1 domain of leucyl-tRNA synthetase (LeuRS) hydrolyses several misactivated amino acids. The CP1 domain of Aquifex aeolicus LeuRS was expressed, purified and crystallized by the hanging-drop vapour-diffusion method using ammonium sulfate as precipitant. Crystals belong to space group P2 1 2 1 2 1 , with unit-cell parameters a = 38.8, b = 98.4, c = 116.7 Å. Crystals diffract to beyond 1.8 Å resolution and contain two monomers in the asymmetric unit. Two CP1 mutants in which a conserved threonine residue essential for the fidelity of the hydrolytic pathway is mutated to alanine or glutamic acid have also been expressed and crystallized. Crystals of the two CP1 mutants are isomorphs of the wild type and diffract to beyond 1.9 Å resolution. All structures were solved by molecular-replacement techniques

Heterogeneous dermatitis complaints after change in drinking water treatment: a case report

Directory of Open Access Journals (Sweden)

Bhatia Rajiv

2006-06-01

Full Text Available Abstract Background The disinfectant monochloramine minimizes the formation of potentially hazardous and regulated byproducts, and many drinking water utilities are shifting to its use. Case presentation After a drinking water utility serving 2.4 million people switched to monochloramine for residual disinfection, a small number of residents complained of dermatitis reactions. We interviewed 17 people about their symptoms. Skin appearance, symptoms, and exposures were heterogeneous. Five respondents had history of hives or rash that preceded the switch to monochloramine. Conclusion The complaints described were heterogeneous, and many of the respondents had underlying or preexisting conditions that would offer plausible alternative explanations for their symptoms. We did not recommend further study of these complaints.

Toward the modeling of combustion reactions through discrete element method (DEM) simulations

Science.gov (United States)

Reis, Martina Costa; Alobaid, Falah; Wang, Yongqi

2018-03-01

In this work, the process of combustion of coal particles under turbulent regime in a high-temperature reaction chamber is modeled through 3D discrete element method (DEM) simulations. By assuming the occurrence of interfacial transport phenomena between the gas and solid phases, one investigates the influence of the physicochemical properties of particles on the rates of heterogeneous chemical reactions, as well as the influence of eddies present in the gas phase on the mass transport of reactants toward the coal particles surface. Moreover, by considering a simplistic chemical mechanism for the combustion process, thermochemical and kinetic parameters obtained from the simulations are employed to discuss some phenomenological aspects of the combustion process. In particular, the observed changes in the mass and volume of coal particles during the gasification and combustion steps are discussed by emphasizing the changes in the chemical structure of the coal. In addition to illustrate how DEM simulations can be used in the modeling of consecutive and parallel chemical reactions, this work also shows how heterogeneous and homogeneous chemical reactions become a source of mass and energy for the gas phase.

Development of 3-D FBR heterogeneous core calculation method based on characteristics method

International Nuclear Information System (INIS)

Takeda, Toshikazu; Maruyama, Manabu; Hamada, Yuzuru; Nishi, Hiroshi; Ishibashi, Junichi; Kitano, Akihiro

2002-01-01

A new 3-D transport calculation method taking into account the heterogeneity of fuel assemblies has been developed by combining the characteristics method and the nodal transport method. In the axial direction the nodal transport method is applied, and the characteristics method is applied to take into account the radial heterogeneity of fuel assemblies. The numerical calculations have been performed to verify 2-D radial calculations of FBR assemblies and partial core calculations. Results are compared with the reference Monte-Carlo calculations. A good agreement has been achieved. It is shown that the present method has an advantage in calculating reaction rates in a small region

Mass transfer in porous media with heterogeneous chemical reaction

Directory of Open Access Journals (Sweden)

Souza S.M.A.G.Ulson de

2003-01-01

Full Text Available In this paper, the modeling of the mass transfer process in packed-bed reactors is presented and takes into account dispersion in the main fluid phase, internal diffusion of the reactant in the pores of the catalyst, and surface reaction inside the catalyst. The method of volume averaging is applied to obtain the governing equation for use on a small scale. The local mass equilibrium is assumed for obtaining the one-equation model for use on a large scale. The closure problems are developed subject to the length-scale constraints and the model of a spatially periodic porous medium. The expressions for effective diffusivity, hydrodynamic dispersion, total dispersion and the Darcy's law permeability tensors are presented. Solution of the set of final equations permits the variations of velocity and concentration of the chemical species along the packed-bed reactors to be obtained.

Heterogeneous reaction of HO2 with airborne TiO2 particles and its implication for climate change mitigation strategies

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D. R. Moon

2018-01-01

Full Text Available One geoengineering mitigation strategy for global temperature rises resulting from the increased concentrations of greenhouse gases is to inject particles into the stratosphere to scatter solar radiation back to space, with TiO2 particles emerging as a possible candidate. Uptake coefficients of HO2, γ(HO2, onto sub-micrometre TiO2 particles were measured at room temperature and different relative humidities (RHs using an atmospheric pressure aerosol flow tube coupled to a sensitive HO2 detector. Values of γ(HO2 increased from 0.021 ± 0.001 to 0.036 ± 0.007 as the RH was increased from 11 to 66 %, and the increase in γ(HO2 correlated with the number of monolayers of water surrounding the TiO2 particles. The impact of the uptake of HO2 onto TiO2 particles on stratospheric concentrations of HO2 and O3 was simulated using the TOMCAT three-dimensional chemical transport model. The model showed that, when injecting the amount of TiO2 required to achieve the same cooling effect as the Mt Pinatubo eruption, heterogeneous reactions between HO2 and TiO2 would have a negligible effect on stratospheric concentrations of HO2 and O3.

Unexpected heterogeneity of BCR-ABL fusion mRNA detected by polymerase chain reaction in Philadelphia chromosome-positive acute lymphoblastic leukemia

International Nuclear Information System (INIS)

Hooberman, A.L.; Carrino, J.J.; Leibowitz, D.; Rowley, J.D.; Le Beau, M.M.; Arlin, Z.A.; Westbrook, C.A.

1989-01-01

The Philadelphia (Ph 1 ) chromosome results in a fusion of portions of the BCR gene from chromosome 22 and the ABL gene from chromosome 9, producing a chimeric BCR-ABL mRNA and protein. In lymphoblastic leukemias, there are two molecular subtypes of the Ph 1 chromosome, one with a rearrangement of the breakpoint cluster region (bcr) of the BCR gene, producing the same 8.5-kilobase BCR-ABL fusion mRNA seen in chronic myelogenous leukemia (CML), and the other, without a bcr rearrangement, producing a 7.0-kilobase BCR-ABL fusion mRNA that is seen only in acute lymphoblastic leukemia (ALL). The authors studied the molecular subtype of the Ph 1 chromosome in 11 cases of Ph 1 -positive ALL, including 2 with a previous diagnosis of CML, using a sensitive method to analyze the mRNA species based on the polymerase chain reaction (PCR). They observed unexpected heterogeneity in BCR-ABL mRNA in this population. They conclude that the PCR gives additional information about the Ph 1 chromosome gene products that cannot be obtained by genomic analysis, but that it cannot be used as the sole means of detection of this chromosomal abnormality in ALL because of the high incidence of false negative results

Active Heterogeneous CaO Catalyst Synthesis from Anadara granosa (Kerang Seashells for Jatropha Biodiesel Production

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Reddy ANR

2017-01-01

Full Text Available Heterogeneous catalysts are often used at large to produce biodiesel from non-edible vegetable crude oils such as Jatropha curcas oil (JCO. In this study, an active heterogeneous CaO catalyst was synthesized from a tropical biodiversity seashells Anadara granosa (A.granosa. The catalytic efficiency of A.granosa CaO was investigated in transesterification of JCO as biodiesel. The A.granosa CaO catalyst was synthesized using ‘Calcination – hydration – dehydration’ protocol. The spectral characterization of the catalyst were investigated by employing FT-IR, SEM, BET and BJH spectrographic techniques. The experimental design was executed with four reaction parameters that include catalyst concentration (CC, methanol ratio (MR, transesterification time (TT and reaction temperature (RT. The JCO transesterification reactions as well as impact of reaction parameters on the Jatropha biodiesel yield (JBY were analyzed. The sufficiency of the experimental results conformed through sequential validation tests, as a result, an average of 96.2% JMY was noted at optimal parametric conditions, CC of 3wt. %, TT of 120 min, MR of 5 mol. and RT of 60ºC at a constant agitation speed of 300rpm. An average JMY of 87.6% was resulted from the A.granosa CaO catalyst during their recycling and reuse studies up to third reuse cycle.

The evolution of function in strictosidine synthase-like proteins.

Science.gov (United States)

Hicks, Michael A; Barber, Alan E; Giddings, Lesley-Ann; Caldwell, Jenna; O'Connor, Sarah E; Babbitt, Patricia C

2011-11-01

The exponential growth of sequence data provides abundant information for the discovery of new enzyme reactions. Correctly annotating the functions of highly diverse proteins can be difficult, however, hindering use of this information. Global analysis of large superfamilies of related proteins is a powerful strategy for understanding the evolution of reactions by identifying catalytic commonalities and differences in reaction and substrate specificity, even when only a few members have been biochemically or structurally characterized. A comparison of >2500 sequences sharing the six-bladed β-propeller fold establishes sequence, structural, and functional links among the three subgroups of the functionally diverse N6P superfamily: the arylesterase-like and senescence marker protein-30/gluconolactonase/luciferin-regenerating enzyme-like (SGL) subgroups, representing enzymes that catalyze lactonase and related hydrolytic reactions, and the so-called strictosidine synthase-like (SSL) subgroup. Metal-coordinating residues were identified as broadly conserved in the active sites of all three subgroups except for a few proteins from the SSL subgroup, which have been experimentally determined to catalyze the quite different strictosidine synthase (SS) reaction, a metal-independent condensation reaction. Despite these differences, comparison of conserved catalytic features of the arylesterase-like and SGL enzymes with the SSs identified similar structural and mechanistic attributes between the hydrolytic reactions catalyzed by the former and the condensation reaction catalyzed by SS. The results also suggest that despite their annotations, the great majority of these >500 SSL sequences do not catalyze the SS reaction; rather, they likely catalyze hydrolytic reactions typical of the other two subgroups instead. This prediction was confirmed experimentally for one of these proteins. Copyright © 2011 Wiley-Liss, Inc.

Phospholipase A/sub 2/ activity towards vesicles of DPPC and DMPC-DSPC containing small amounts of SMPC

DEFF Research Database (Denmark)

Høyrup, Lise Pernille Kristine; Mouritsen, Ole G.; Jørgensen, Kent

2001-01-01

Phospholipase A/sub 2/ (PLA/sub 2/) is an interfacially active enzyme whose hydrolytic activity is known to be enhanced in one-component phospholipid bilayer substrates exhibiting dynamic micro-heterogeneity. In this study the activity of PLA/sub 2/ towards large unilamellar vesicles composed of ...

Effect of the crude extract of Eugenia uniflora in morphogenesis and secretion of hydrolytic enzymes in Candida albicans from the oral cavity of kidney transplant recipients.

Science.gov (United States)

Silva-Rocha, Walicyranison Plinio; de Brito Lemos, Vitor Luiz; Ferreira, Magda Rhayanny Assunção; Soares, Luiz Alberto Lira; Svidzisnki, Terezinha Inês Estivalet; Milan, Eveline Pipolo; Chaves, Guilherme Maranhão

2015-02-05

Candida albicans is a diploid yeast that in some circumstances may cause oral or oropharyngeal infections. Yeasts virulence factors contribute for both the maintenance of colonizing strains in addition to damage and cause tissue invasion, thus the establishment of infection occurs. The limited arsenal of antifungal drugs for the treatment of candidiasis turn the investigation of natural products mandatory for the discovery of new targets for antifungal drug development. Therefore, tropical countries emerge as important providers of natural products with potential antimicrobial activity. This study aimed to investigate morphogenesis and secretion of hydrolytic enzymes (phospholipase and proteinase) in the presence of the CE of Eugenia uniflora. The isolates were tested for their ability to form hyphae in both solid and liquid media under three different conditions: YPD + 20% FBS, Spider medium and GlcNac and the ability to secrete phospholipase and proteinase in the presence of 2000 μg/mL of E. uniflora. The CE of E. uniflora inhibited hypha formation in both liquid and solid media tested. It also impaired hydrolytic enzymes production. This was the first study to describe the interaction of a natural product with the full expression of three different factors in C. albicans. E. uniflora may be an alternative therapeutic for oral candidiasis in the future.

Influence of the Morphology of Core-Shell Supports on the Immobilization of Lipase B from Candida antarctica

Directory of Open Access Journals (Sweden)

Martina C. C. Pinto

2014-08-01

Full Text Available Core-shell polymer particles with different properties were produced through combined suspension-emulsion polymerizations and employed as supports for immobilization of lipase B from Candida antarctica. In order to evaluate how the morphology of the particles affects the immobilization parameters, empirical models were developed to describe the performance of the biocatalysts as a function of the specific area, volume of pores and average pore diameter of the supports. It was observed that the average pore sizes did not affect the enzymatic activities in the analyzed range of pore sizes. It was also observed that the increase of the specific area (and of the volume of pores led to higher enzyme loadings, also leading to an increase in the esterification activity, as expected. However, when the specific area (and volume of pores increased, the hydrolytic activity and the retention of hydrolytic activity of the biocatalysts decreased, indicating the existence of diffusional limitations for some hydrolytic reactions, probably because of the high reaction rates.

A New Bioinspired Perchlorate Reduction Catalyst with Significantly Enhanced Stability via Rational Tuning of Rhenium Coordination Chemistry and Heterogeneous Reaction Pathway.

Science.gov (United States)

Liu, Jinyong; Han, Mengwei; Wu, Dimao; Chen, Xi; Choe, Jong Kwon; Werth, Charles J; Strathmann, Timothy J

2016-06-07

Rapid reduction of aqueous ClO4(-) to Cl(-) by H2 has been realized by a heterogeneous Re(hoz)2-Pd/C catalyst integrating Re(O)(hoz)2Cl complex (hoz = oxazolinyl-phenolato bidentate ligand) and Pd nanoparticles on carbon support, but ClOx(-) intermediates formed during reactions with concentrated ClO4(-) promote irreversible Re complex decomposition and catalyst deactivation. The original catalyst design mimics the microbial ClO4(-) reductase, which integrates Mo(MGD)2 complex (MGD = molybdopterin guanine dinucleotide) for oxygen atom transfer (OAT). Perchlorate-reducing microorganisms employ a separate enzyme, chlorite dismutase, to prevent accumulation of the destructive ClO2(-) intermediate. The structural intricacy of MGD ligand and the two-enzyme mechanism for microbial ClO4(-) reduction inspired us to improve catalyst stability by rationally tuning Re ligand structure and adding a ClOx(-) scavenger. Two new Re complexes, Re(O)(htz)2Cl and Re(O)(hoz)(htz)Cl (htz = thiazolinyl-phenolato bidentate ligand), significantly mitigate Re complex decomposition by slightly lowering the OAT activity when immobilized in Pd/C. Further stability enhancement is then obtained by switching the nanoparticles from Pd to Rh, which exhibits high reactivity with ClOx(-) intermediates and thus prevents their deactivating reaction with the Re complex. Compared to Re(hoz)2-Pd/C, the new Re(hoz)(htz)-Rh/C catalyst exhibits similar ClO4(-) reduction activity but superior stability, evidenced by a decrease of Re leaching from 37% to 0.25% and stability of surface Re speciation following the treatment of a concentrated "challenge" solution containing 1000 ppm of ClO4(-). This work demonstrates the pivotal roles of coordination chemistry control and tuning of individual catalyst components for achieving both high activity and stability in environmental catalyst applications.

Systematic Analysis of the Effect of Small Scale Permeability Heterogeneity on Hyporheic Exchange Flux and Residence Times

Science.gov (United States)

Laube, G.; Schmidt, C.; Fleckenstein, J. H.

2014-12-01

The hyporheic zone (HZ) contributes significantly to whole stream biogeochemical cycling. Biogeochemical reactions within the HZ are often transport limited, thus, understanding these reactions requires knowledge about the magnitude of hyporheic fluxes (HF) and the residence time (RT) of these fluxes within the HZ. While the hydraulics of HF are relatively well understood, studies addressing the influence of permeability heterogeneity lack systematic analysis and have even produced contradictory results (e.g. [1] vs. [2]). In order to close this gap, this study uses a statistical numerical approach to elucidate the influence of permeability heterogeneity on HF and RT. We simulated and evaluated 3750 2D-scenarios of sediment heterogeneity by means of Gaussian random fields with focus on total HF and RT distribution. The scenarios were based on ten realizations of each of all possible combinations of 15 different correlation lengths, 5 dipping angles and 5 permeability variances. Roughly 500 hyporheic stream traces were analyzed per simulation, for a total of almost two million stream traces analyzed for correlations between permeability heterogeneity, HF, and RT. Total HF and the RT variance positively correlated with permeability variance while the mean RT negatively correlated with permeability variance. In contrast, changes in correlation lengths and dipping angles had little effect on the examined properties RT and HF. These results provide a possible explanation of the seemingly contradictory conclusions of recent studies, given that the permeability variances in these studies differ by several orders of magnitude. [1] Bardini, L., Boano, F., Cardenas, M.B, Sawyer, A.H, Revelli, R. and Ridolfi, L. "Small-Scale Permeability Heterogeneity Has Negligible Effects on Nutrient Cycling in Streambeds." Geophysical Research Letters, 2013. doi:10.1002/grl.50224. [2] Zhou, Y., Ritzi, R. W., Soltanian, M. R. and Dominic, D. F. "The Influence of Streambed Heterogeneity on

Kinetics of catalytic reactions solutions manual

CERN Document Server

Vannice, M Albert

2005-01-01

Including countless exercises and worked examples, this advanced reference work and textbook will be extremely useful for the work of many industrial scientists. It teaches readers to design kinetic experiments involving heterogeneous catalysts, to characterize these catalysts, to acquire rate data, to find heat and mass transfer limitations in these data, to select reaction models, to derive rate expressions based on these models, and to assess the consistency of these rate equations.

A library of prompt detonation reaction zone data

Energy Technology Data Exchange (ETDEWEB)

Souers, P. C., LLNL

1998-06-01

Tables are given listing literature data that allows calculation of sonic reaction zones at or near steady-state for promptly detonating explosive cylinders. The data covers homogeneous, heterogeneous, composite, inorganic and binary explosives and allows comparison across the entire explosive field. Table 1 lists detonation front curvatures. Table 2 lists Size Effect data, i.e. the change of detonation velocity with cylinder radius. Table 3 lists failure radii and detonation velocities. Table 4 lists explosive compositions. A total of 51 references dating back into the 1950`s are given. Calculated reaction zones, radii of curvature and growth rate coefficients are listed.

Quantitative iTRAQ secretome analysis of Aspergillus niger reveals novel hydrolytic enzymes.

Science.gov (United States)

Adav, Sunil S; Li, An A; Manavalan, Arulmani; Punt, Peter; Sze, Siu Kwan

2010-08-06

The natural lifestyle of Aspergillus niger made them more effective secretors of hydrolytic proteins and becomes critical when this species were exploited as hosts for the commercial secretion of heterologous proteins. The protein secretion profile of A. niger and its mutant at different pH was explored using iTRAQ-based quantitative proteomics approach coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS). This study characterized 102 highly confident unique proteins in the secretome with zero false discovery rate based on decoy strategy. The iTRAQ technique identified and relatively quantified many hydrolyzing enzymes such as cellulases, hemicellulases, glycoside hydrolases, proteases, peroxidases, and protein translocating transporter proteins during fermentation. The enzymes have potential application in lignocellulosic biomass hydrolysis for biofuel production, for example, the cellulolytic and hemicellulolytic enzymes glucan 1,4-alpha-glucosidase, alpha-glucosidase C, endoglucanase, alpha l-arabinofuranosidase, beta-mannosidase, glycosyl hydrolase; proteases such as tripeptidyl-peptidase, aspergillopepsin, and other enzymes including cytochrome c oxidase, cytochrome c oxidase, glucose oxidase were highly expressed in A. niger and its mutant secretion. In addition, specific enzyme production can be stimulated by controlling pH of the culture medium. Our results showed comprehensive unique secretory protein profile of A. niger, its regulation at different pH, and the potential application of iTRAQ-based quantitative proteomics for the microbial secretome analysis.

Hydrolytic enzymes production by Aspergillus section Nigri in presence of butylated hydroxyanisole and propyl paraben on peanut meal extract agar.

Science.gov (United States)

Barberis, Carla L; Landa, María F; Barberis, Mauricio G; Giaj-Merlera, Guillermo; Dalcero, Ana M; Magnoli, Carina E

2014-01-01

In the last years, food grade antioxidants are used safely as an alternative to traditional fungicides to control fungal growth in several food and agricultural products. In this work, the effect of butylated hydroxyanisole (BHA) and propyl paraben (PP) on two hydrolytic enzyme activity (β-d-glucosidase and α-d-galactosidase) by Aspergillus section Nigri species under different water activity conditions (aW; 0.98, 0.95 and 0.93) and incubation time intervals (24, 48, 72 and 96h) was evaluated on peanut-based medium. The activity of two glycosidases, β-d-glucosidase and α-d-galactosidase, was assayed using as substrates 4-nitrophenyl-β-d-glucopyranosido and 4-nitrophenyl-α-d-galactopyranosido, respectively. The enzyme activity was determined by the increase in optical density at 405nm caused by the liberation of p-nitrophenol by enzymatic hydrolysis of the substrate. Enzyme activity was expressed as micromoles of p-nitrophenol released per minute. The major inhibition in β-d-glucosidase activity of A. carbonarius and A. niger was found with 20mmoll(-1) of BHA or PP at 0.98 and 0.95 aW, respectively, whereas for α-d-galactosidase activity a significant decrease in enzyme activity with respect to control was observed in A. carbonarius among 5 to 20mmoll(-1) of BHA or PP in all conditions assayed. Regarding A. niger, the highest percentages of enzyme inhibition activity were found with 20mmoll(-1) of BHA or PP at 0.95 aW and 96h. The results of this work provide information about the capacity of BHA and PP to inhibit in vitro conditions two of the most important hydrolytic enzymes produced by A. carbonarius and A. niger species. Copyright © 2012 Revista Iberoamericana de Micología. Published by Elsevier Espana. All rights reserved.

Modified natural zeolite as heterogeneous Fenton catalyst in treatment of recalcitrants in industrial effluent

Directory of Open Access Journals (Sweden)

Milton M. Arimi

2017-04-01

Full Text Available Industrial effluents with high recalcitrants should undergo post-treatment after biological treatment. The aim of this study was to use cheap and abundantly available natural materials to develop heterogeneous Fenton catalysts for the removal of colored recalcitrants in molasses distillery wastewater (MDW. The pellets of zeolite, which is naturally available in many countries, were modified by pre-treatment with sulphuric acid, nitric acid and hydrochloric acid, before embedding on them the ferrous ions. The effects of pH and temperature on heterogeneous Fenton were studied using the modified catalysts. The sulphuric acid-ferrous modified catalysts showed the highest affectivity which achieved 90% color and 60% TOC (total organic carbon removal at 150 g/L pellet catalyst dosage, 2 g/L H2O2 and 25 °C. The heterogeneous Fenton with the same catalyst caused improvement in the biodegradability of anaerobic effluent from 0.07 to 0.55. The catalyst was also applied to pre-treat the raw MDW and increased it's biodegradability by 4%. The color of the resultant anaerobic effluent was also reduced. The kinetics of total TOC removal was found to depend on operation temperature. It was best described by simultaneous first and second order kinetics model for the initial reaction and second order model for the rest of the reaction.

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Science.gov (United States)

Liu, Lichen; Corma, Avelino

2018-05-23

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal-support interaction, and metal-reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results obtained from different systems and try to give a picture on how different types of metal species work in different reactions and give perspectives on the future directions toward better understanding of the catalytic behavior of different metal entities (single atoms, nanoclusters, and nanoparticles) in a unifying manner.

Mechanical behaviour׳s evolution of a PLA-b-PEG-b-PLA triblock copolymer during hydrolytic degradation.

Science.gov (United States)

Breche, Q; Chagnon, G; Machado, G; Girard, E; Nottelet, B; Garric, X; Favier, D

2016-07-01

PLA-b-PEG-b-PLA is a biodegradable triblock copolymer that presents both the mechanical properties of PLA and the hydrophilicity of PEG. In this paper, physical and mechanical properties of PLA-b-PEG-b-PLA are studied during in vitro degradation. The degradation process leads to a mass loss, a decrease of number average molecular weight and an increase of dispersity index. Mechanical experiments are made in a specific experimental set-up designed to create an environment close to in vivo conditions. The viscoelastic behaviour of the material is studied during the degradation. Finally, the mechanical behaviour is modelled with a linear viscoelastic model. A degradation variable is defined and included in the model to describe the hydrolytic degradation. This variable is linked to physical parameters of the macromolecular polymer network. The model allows us to describe weak deformations but become less accurate for larger deformations. The abilities and limits of the model are discussed. Copyright © 2016 Elsevier Ltd. All rights reserved.

Heterogeneous network architectures

DEFF Research Database (Denmark)

Christiansen, Henrik Lehrmann

2006-01-01

is flexibility. This thesis investigates such heterogeneous network architectures and how to make them flexible. A survey of algorithms for network design is presented, and it is described how using heuristics can increase the speed. A hierarchical, MPLS based network architecture is described......Future networks will be heterogeneous! Due to the sheer size of networks (e.g., the Internet) upgrades cannot be instantaneous and thus heterogeneity appears. This means that instead of trying to find the olution, networks hould be designed as being heterogeneous. One of the key equirements here...... and it is discussed that it is advantageous to heterogeneous networks and illustrated by a number of examples. Modeling and simulation is a well-known way of doing performance evaluation. An approach to event-driven simulation of communication networks is presented and mixed complexity modeling, which can simplify...

The chemistry of bromine in the stratosphere: Influence of a new rate constant for the reaction BrO + HO2

Science.gov (United States)

Pirre, Michel; Marceau, Francois J.; Lebras, Georges; Maguin, Francoise; Poulet, Gille; Ramaroson, Radiela

1994-01-01

The impact of new laboratory data for the reaction BrO + HO2 yields HOBr + O2 in the depletion of global stratospheric ozone has been estimated using a one-dimensional photochemical model taking into account the heterogeneous reaction on sulphate aerosols which converts N2O5 into HNO3. Assuring an aerosol loading 2 times as large as the 'background' and a reaction probability of 0.1 for the above heterogeneous reaction, the 6 fold increase in the measured rate constant for the reaction of BrO with HO2 increases the computed depletion of global ozone produced by 20 ppt of total bromine from 2.01 percent to 2.36 percent. The use of the higher rate constant increases the HOBr mixing ratio and makes the bromine partitioning and the ozone depletion very sensitive to the branching ratio of the potential channel forming HBr in the BrO + HO2 reaction.

A novel hydrolytic product from flesh of Mactra veneriformis and its bioactivities in calcium supplement

Science.gov (United States)

Wang, Lingchong; Chen, Shiyong; Liu, Rui; Wu, Hao

2012-09-01

To prepare calcium-binding peptides, the flesh residue of Mactra Veneriformis was subjected to enzymatic hydrolysis. By comparing the capability of combining calcium of the hydrolyzates, pepsin was confirmed to be the most suitable enzyme for hydrolyzing the flesh residue to release calcium-binding peptides among the seven tested proteases. The pepsin hydrolyzate (PHM) was divided into three fractions according to the molecule weight of its composition, which ranged from 0.5 to 15 kDa. The low-molecule-weight fraction named PHM-3 had the highest capability in combining calcium. The peptides existing in the PHM-3 fraction consisted of higher contents of Glu, Ala and Leu, and could produce one type of calcium-peptide complex by powerfully chelating calcium ions. PHM-3 products could effectively increase calcium absorption and retention while they decreased the calcium excretion in animal tests. Additionally, symptoms caused by low calcium bioavailability in ovariectomized rats, such as bone mineral density reduction and mechanical strength loss could be significantly ameliorated by the hydrolytic products addition in diet.

Stimulation of the hydrolytic stage for biogas production from cattle manure in an electrochemical bioreactor.

Science.gov (United States)

Samani, Saeed; Abdoli, Mohammad Ali; Karbassi, Abdolreza; Amin, Mohammad Mehdi

Electrical current in the hydrolytic phase of the biogas process might affect biogas yield. In this study, four 1,150 mL single membrane-less chamber electrochemical bioreactors, containing two parallel titanium plates were connected to the electrical source with voltages of 0, -0.5, -1 and -1.5 V, respectively. Reactor 1 with 0 V was considered as a control reactor. The trend of biogas production was precisely checked against pH, oxidation reduction potential and electrical power at a temperature of 37 ± 0.5°C amid cattle manure as substrate for 120 days. Biogas production increased by voltage applied to Reactors 2 and 3 when compared with the control reactor. In addition, the electricity in Reactors 2 and 3 caused more biogas production than Reactor 4. Acetogenic phase occurred more quickly in Reactor 3 than in the other reactors. The obtained results from Reactor 4 were indicative of acidogenic domination and its continuous behavior under electrical stimulation. The results of the present investigation clearly revealed that phasic electrical current could enhance the efficiency of biogas production.

Hydroalumination of Ketenimines and Subsequent Reactions with Heterocumulenes: Synthesis of Unsaturated Amide Derivatives and 1,3-Diimines.

Science.gov (United States)

Jin, Xing; Willeke, Matthias; Lucchesi, Ralph; Daniliuc, Constantin-Gabriel; Fröhlich, Roland; Wibbeling, Birgit; Uhl, Werner; Würthwein, Ernst-Ulrich

2015-06-19

The series of differently substituted ketenimines 1 was hydroluminated using di-iso-butyl aluminum hydride. For the sterically congested ketenimine 1a, preferred hydroalumination of the C═N-bond was proven by X-ray crystallography (compound 5a). In situ treatment of the hydroaluminated ketenimines 5 with various heterocumulenes like carbodiimides, isocycanates, isothiocyanates and ketenimines as electrophiles and subsequent hydrolytic workup resulted in novel enamine derived amide species in case of N-attack (sterically less hindered ketenimines) under formation of a new C-N-bond or in 1,3-diimines by C-C-bond-formation in case of bulky substituents at the ketenimine-nitrogen atom. Furthermore, domino reactions with more than 1 equiv of the electrophile or by subsequent addition of two different electrophiles are possible and lead to polyfunctional amide derivatives of the biuret type which are otherwise not easily accessible.

Isotopic constraints on heterogeneous sulfate production in Beijing haze

Science.gov (United States)

He, Pengzhen; Alexander, Becky; Geng, Lei; Chi, Xiyuan; Fan, Shidong; Zhan, Haicong; Kang, Hui; Zheng, Guangjie; Cheng, Yafang; Su, Hang; Liu, Cheng; Xie, Zhouqing

2018-04-01

Discerning mechanisms of sulfate formation during fine-particle pollution (referred to as haze hereafter) in Beijing is important for understanding the rapid evolution of haze and for developing cost-effective air pollution mitigation strategies. Here we present observations of the oxygen-17 excess of PM2.5 sulfate (Δ17O(SO42-)) collected in Beijing haze from October 2014 to January 2015 to constrain possible sulfate formation pathways. Throughout the sampling campaign, the 12-hourly averaged PM2.5 concentrations ranged from 16 to 323 µg m-3 with a mean of (141 ± 88 (1σ)) µg m-3, with SO42- representing 8-25 % of PM2.5 mass. The observed Δ17O(SO42-) varied from 0.1 to 1.6 ‰ with a mean of (0.9 ± 0.3) ‰. Δ17O(SO42-) increased with PM2.5 levels in October 2014 while the opposite trend was observed from November 2014 to January 2015. Our estimate suggested that in-cloud reactions dominated sulfate production on polluted days (PDs, PM2.5 ≥ 75 µg m-3) of Case II in October 2014 due to the relatively high cloud liquid water content, with a fractional contribution of up to 68 %. During PDs of Cases I and III-V, heterogeneous sulfate production (Phet) was estimated to contribute 41-54 % to total sulfate formation with a mean of (48 ± 5) %. For the specific mechanisms of heterogeneous oxidation of SO2, chemical reaction kinetics calculations suggested S(IV) ( = SO2 ⚫ H2O + HSO3- + SO32-) oxidation by H2O2 in aerosol water accounted for 5-13 % of Phet. The relative importance of heterogeneous sulfate production by other mechanisms was constrained by our observed Δ17O(SO42-). Heterogeneous sulfate production via S(IV) oxidation by O3 was estimated to contribute 21-22 % of Phet on average. Heterogeneous sulfate production pathways that result in zero-Δ17O(SO42-), such as S(IV) oxidation by NO2 in aerosol water and/or by O2 via a radical chain mechanism, contributed the remaining 66-73 % of Phet. The assumption about the thermodynamic state of aerosols

Heterogeneous oxidation of saturated organic aerosols by hydroxyl radicals: uptake kinetics, condensed-phase products, and particle size change

Directory of Open Access Journals (Sweden)

I. J. George

2007-08-01

Full Text Available The kinetics and reaction mechanism for the heterogeneous oxidation of saturated organic aerosols by gas-phase OH radicals were investigated under NO_x-free conditions. The reaction of 150 nm diameter Bis(2-ethylhexyl sebacate (BES particles with OH was studied as a proxy for chemical aging of atmospheric aerosols containing saturated organic matter. An aerosol reactor flow tube combined with an Aerodyne time-of-flight aerosol mass spectrometer (ToF-AMS and scanning mobility particle sizer (SMPS was used to study this system. Hydroxyl radicals were produced by 254 nm photolysis of O₃ in the presence of water vapour. The kinetics of the heterogeneous oxidation of the BES particles was studied by monitoring the loss of a mass fragment of BES with the ToF-AMS as a function of OH exposure. We measured an initial OH uptake coefficient of γ₀=1.3 (±0.4, confirming that this reaction is highly efficient. The density of BES particles increased by up to 20% of the original BES particle density at the highest OH exposure studied, consistent with the particle becoming more oxidized. Electrospray ionization mass spectrometry analysis showed that the major particle-phase reaction products are multifunctional carbonyls and alcohols with higher molecular weights than the starting material. Volatilization of oxidation products accounted for a maximum of 17% decrease of the particle volume at the highest OH exposure studied. Tropospheric organic aerosols will become more oxidized from heterogeneous photochemical oxidation, which may affect not only their physical and chemical properties, but also their hygroscopicity and cloud nucleation activity.

Effect of Support in Heterogeneous Ruthenium Catalysts Used for the Selective Aerobic Oxidation of HMF in Water

DEFF Research Database (Denmark)

Gorbanev, Yury; Kegnæs, Søren; Riisager, Anders

2011-01-01

Heterogeneous ruthenium-based catalysts were applied in the selective, aerobic oxidation of 5-hydroxymethylfurfural, a versatile biomass-derived chemical, to form 2,5-furandicarboxylic acid. The oxidation reactions were performed in water with dioxygen as the oxidant at different pressures without...

Triangular Diagrams Teach Steady and Dynamic Behaviour of Catalytic Reactions.

Science.gov (United States)

Klusacek, K.; And Others

1989-01-01

Illustrates how triangular diagrams can aid in presenting some of the rather complex transient interactions that occur among gas and surface species during heterogeneous catalytic reactions. The basic equations and numerical examples are described. Classroom use of the triangular diagram is discussed. Several diagrams and graphs are provided. (YP)

AN INTEGRATED, ANIMATED MODEL OF THE (NA, K-ATPase HYDROLYTIC CYCLE

Directory of Open Access Journals (Sweden)

F.A. Leone

2006-07-01

Full Text Available The  (Na,  K-ATPase,  or  sodium  pump,  is  the  principal,  active  transport  system  that  establishes  sodium  and potassium  gradients  across  the  plasma  membranes  of  all  animal  cells.  Such  gradients  are  critical  to  sustaining important cellular functions like osmotic equilibrium, cell volume and pH homeostasis, among many others (Ann Rev Physiol 65: 817, 2003; Physiol 19: 377, 2004. This transport protein is a heterodimer that consists of a 110-kDa  -subunit  and  a  55-kDa,  glycosylated  -subunit.  A  group  of  seven  small  proteins,  known  as  FXYD  proteins  from  the sequence  of  a  conserved  motif  has  been  identified  recently,  and  one  of  these,  FXYD2,  constitutes  the  (Na,  K-ATPase  -subunit.  Our  model  is  based  on  conformational  changes  occurring  between  the  E1  and  E2  forms  of  the enzyme, which initiates its hydrolytic cycle at a high ATP/ADP ratio. While all steps are reversible, the model does not include  the reverse  reactions that can  take  place under appropriate conditions. The  E1 state  corresponds to that of the SERCA, recently crystallized (Science 304; 1672, 2004; Nature 430: 529, 2004. The animation was developed in Macromedia  Flash  8.0® and  illustrates  the  principle  of  an  alternating-access  model  of  an  ion  pump.  The  protein  is embedded  in  the  membrane  with  the  extracellular  face  uppermost  and  the  cytoplasmic  face  at  the  bottom.  Access from  the  cytoplasmic  or  extracellular  faces  to  the  cation-binding  sites,  located  in  the  transmembrane  moiety,  are controlled  by  two  gates  (moving  horizontal  bars,  and  conformations  showing  the  two  gates  closed  correspond  to states with occluded Na+ and K+ sites. Changes in cation-binding site structure entail

EFFECTS OF PORE STRUCTURE CHANGE AND MULTI-SCALE HETEROGENEITY ON CONTAMINANT TRANSPORT AND REACTION RATE UPSCALING

Energy Technology Data Exchange (ETDEWEB)

Peters, Catherine A [Princeton University

2013-05-15

This project addressed the scaling of geochemical reactions to core and field scales, and the interrelationship between reaction rates and flow in porous media. We targeted reactive transport problems relevant to the Hanford site specifically the reaction of highly caustic, radioactive waste solutions with subsurface sediments, and the immobilization of 90Sr and 129I through mineral incorporation and passive flow blockage, respectively. We addressed the correlation of results for pore-scale fluid-soil interaction with field-scale fluid flow, with the specific goals of (i) predicting attenuation of radionuclide concentration; (ii) estimating changes in flow rates through changes of soil permeabilities; and (iii) estimating effective reaction rates. In supplemental work, we also simulated reactive transport systems relevant to geologic carbon sequestration. As a whole, this research generated a better understanding of reactive transport in porous media, and resulted in more accurate methods for reaction rate upscaling and improved prediction of permeability evolution. These scientific advancements will ultimately lead to better tools for management and remediation of DOE legacy waste problems.

Intratumoral Heterogeneity of MicroRNA Expression in Rectal Cancer

DEFF Research Database (Denmark)

Eriksen, Anne Haahr Mellergaard; Andersen, Rikke Fredslund; Nielsen, Boye Schnack

2016-01-01

study was to assess the heterogeneity of a panel of selected miRNAs in rectal cancer, using two different technical approaches. MATERIALS AND METHODS: The expression of the investigated miRNAs was analysed by real-time quantitative polymerase chain reaction (RT-qPCR) and in situ hybridization (ISH......) in tumour specimens from 27 patients with T3-4 rectal cancer. From each tumour, tissue from three different luminal localisations was examined. Inter- and intra-patient variability was assessed by calculating intraclass correlation coefficients (ICCs). Correlations between RT-qPCR and ISH were evaluated...

Heterogeneous Effects of a Nonlinear Price Schedule for Outpatient Care.

Science.gov (United States)

Farbmacher, Helmut; Ihle, Peter; Schubert, Ingrid; Winter, Joachim; Wuppermann, Amelie

2017-10-01

Nonlinear price schedules generally have heterogeneous effects on health-care demand. We develop and apply a finite mixture bivariate probit model to analyze whether there are heterogeneous reactions to the introduction of a nonlinear price schedule in the German statutory health insurance system. In administrative insurance claims data from the largest German health insurance plan, we find that some individuals strongly react to the new price schedule while a second group of individuals does not react. Post-estimation analyses reveal that the group of the individuals who do not react to the reform includes the relatively sick. These results are in line with forward-looking behavior: Individuals who are already sick expect that they will hit the kink in the price schedule and thus are less sensitive to the co-payment. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

Investigations on the heterogenous catalytic hydrogenation using isotope effect and gamma- and neutron radiation

Energy Technology Data Exchange (ETDEWEB)

Kudlacek, R; Cabicar, J [Ceske Vysoke Uceni Technicke, Prague (Czechoslovakia). Katedra Jaderne Chemie

1976-01-01

The kinetic and solvent isotope effects during the maleic acid heterogeneous catalytic hydrogenation and deuteration in light and heavy water have been studied. Also the effect of the gamma and neutron irradiation on the Ni-ZnO catalysts (with various ratios of components) on the reaction kinetics and mechanism has been measured, as well as the effect of pH on the adsorption behaviour of maleic acid and the temperature dependence of the reaction rate. Existence of different adsorption centers for hydrogen and maleic acid could be deduced from these experiments. A reaction mechanism based on the two-dimensional diffusion of components in the surface is proposed. The catalyst is formed from Ni and ZnO-microspheres. Hydrogen is bound to nickel and maleic acid is adsorbed on the ZnO-microspheres. The reaction takes place on the boundary layers of these microspheres.

Gas-surface interactions and heterogeneous chemistry on interstellar grains analogues

Directory of Open Access Journals (Sweden)

Cazaux S.

2012-01-01

Full Text Available Detailed laboratory studies and progress in surface science technique, have allowed in recent years the first experimental confirmation of surface reaction schemes, as introduced by Tielens, Hagen and Charnley [1,2]. In this paper, we review few heterogeneous processes which give routes to form elementary molecules considered as precursors for explaining the variety and richness of molecular species in the interstellar medium. Adsorption, diffusion and reaction processes are discussed. With emphasis on the experimental approaches, but also supported by theoretical developments, progresses in the understanding of the “catalytic role” of a dust grain surface in various physical conditions are described. Recent advances made on few important species (H2, H2O, CH3OH are used to illustrate basic properties and raise open questions.

Adjoint spectrum calculation in fuel heterogeneous cells

International Nuclear Information System (INIS)

Suster, Luis Carlos

1998-01-01

In most codes for cells calculation, the multigroup cross sections are generated taking into consideration the conservation of the reaction rates in the forward spectrum. However, for certain uses of the perturbation theory it's necessary to use the average of the parameters for energy macrogroups over the forward and the adjoint spectra. In this thesis the adjoint spectrum was calculated from the adjoint neutron balance equations, that were obtained for a heterogeneous unit cell. The collision probabilities method was used to obtain these equations. In order optimize the computational run-time, the Gaussian quadrature method was used in the calculation of the neutron balance equations, forward and adjoint. This method of integration was also used for the Doppler broadening functions calculation, necessary for obtaining the energy dependent cross sections. In order to calculate the reaction rates and the average cross sections, using both the forward and the adjoint neutron spectra, the most important resonances of the U 238 were considered. The results obtained with the method show significant differences for the different cross sections weighting schemes. (author)

Characterizing physical properties and heterogeneous chemistry of single particles in air using optical trapping-Raman spectroscopy

Science.gov (United States)

Gong, Z.; Wang, C.; Pan, Y. L.; Videen, G.

2017-12-01

Heterogeneous reactions of solid particles in a gaseous environment are of increasing interest; however, most of the heterogeneous chemistry studies of airborne solids were conducted on particle ensembles. A close examination on the heterogeneous chemistry between single particles and gaseous-environment species is the key to elucidate the fundamental mechanisms of hydroscopic growth, cloud nuclei condensation, secondary aerosol formation, etc., and reduce the uncertainty of models in radiative forcing, climate change, and atmospheric chemistry. We demonstrate an optical trapping-Raman spectroscopy (OT-RS) system to study the heterogeneous chemistry of the solid particles in air at single-particle level. Compared to other single-particle techniques, optical trapping offers a non-invasive, flexible, and stable method to isolate single solid particle from substrates. Benefited from two counter-propagating hollow beams, the optical trapping configuration is adaptive to trap a variety of particles with different materials from inorganic substitution (carbon nanotubes, silica, etc.) to organic, dye-doped polymers and bioaerosols (spores, pollen, etc.), with different optical properties from transparent to strongly absorbing, with different sizes from sub-micrometers to tens of microns, or with distinct morphologies from loosely packed nanotubes to microspheres and irregular pollen grains. The particles in the optical trap may stay unchanged, surface degraded, or optically fragmented according to different laser intensity, and their physical and chemical properties are characterized by the Raman spectra and imaging system simultaneously. The Raman spectra is able to distinguish the chemical compositions of different particles, while the synchronized imaging system can resolve their physical properties (sizes, shapes, morphologies, etc.). The temporal behavior of the trapped particles also can be monitored by the OT-RS system at an indefinite time with a resolution from

Dynamic heterogeneity in life histories

DEFF Research Database (Denmark)

Tuljapurkar, Shripad; Steiner, Uli; Orzack, Steven Hecht

2009-01-01

or no fixed heterogeneity influences this trait. We propose that dynamic heterogeneity provides a 'neutral' model for assessing the possible role of unobserved 'quality' differences between individuals. We discuss fitness for dynamic life histories, and the implications of dynamic heterogeneity...... generate dynamic heterogeneity: life-history differences produced by stochastic stratum dynamics. We characterize dynamic heterogeneity in a range of species across taxa by properties of the Markov chain: the entropy, which describes the extent of heterogeneity, and the subdominant eigenvalue, which...... distributions of lifetime reproductive success. Dynamic heterogeneity contrasts with fixed heterogeneity: unobserved differences that generate variation between life histories. We show by an example that observed distributions of lifetime reproductive success are often consistent with the claim that little...

A fast, sensitive and easy colorimetric assay for chitinase and cellulase activity detection.

NARCIS (Netherlands)

Ferrari, Alessandro; Gaber, Yasser; Fraaije, Marco

2014-01-01

BACKGROUND: Most of the current colorimetric methods for detection of chitinase or cellulase activities on the insoluble natural polymers chitin and cellulose depend on a chemical redox reaction. The reaction involves the reducing ends of the hydrolytic products. The Schales' procedure and the

Nucleation reactions during deformation and crystallization of metallic glass

International Nuclear Information System (INIS)

Perepezko, J.H.; Imhoff, S.D.; Chen, M.W.; Gonzalez, S.; Inoue, A.

2012-01-01

Highlights: ► New approach to the examination and analysis of shear band nucleation. ► Discovery of multiple shear band nucleation sites. ► Identification of a method of using transient kinetic behavior to provide a more realistic evaluation of the diffusivity that is relevant to nucleation. - Abstract: Nucleation reactions play a central role in the synthesis of both bulk metallic glasses and nanostructured materials. For nanostructured materials it is necessary to promote a high nucleation density without significant growth or coarsening. Beyond crystallization reactions nucleation of shear bands is critical for promoting a homogeneous flow and useful ductility for structural applications of bulk metallic glass. The study and analysis of nucleation reactions for these different situations requires a consideration of the stochastic nature of nucleation, the influence of heterogeneous sites, and the controlling transport properties. For shear band nucleation, the stochastic nature can be effectively probed by instrumented nanoindentation tests. The analysis of a statistically significant number of measurements of the first pop-in shear band nucleation events reveals at least two main nucleation sites. In nanostructured composites, the initial nucleation stage is influenced by transient effects as reflected in the delay time prior to steady state nucleation and by heterogeneous nucleation sites that are related to medium range order regions in Al-base amorphous alloys. Moreover, the early growth characteristics are linked to the maximum achievable particle density. The new developments and insight on the fundamental understanding of nanostructure reaction mechanisms offer valuable guidance for control of nanoscale microstructures and for promoting ductile deformation behavior.

Brønsted instead of Lewis acidity in functionalized MIL-101Cr MOFs for efficient heterogeneous (nano-MOF) catalysis in the condensation reaction of aldehydes with alcohols.

Science.gov (United States)

Herbst, Annika; Khutia, Anupam; Janiak, Christoph

2014-07-21

Porous chromium(III) 2-nitro-, 2-amino-, and nonfunctionalized terephthalate (MIL-101Cr) metal organic frameworks are heterogeneous catalysts for diacetal formation from benzaldehyde and methanol (B-M reaction) as well as other aldehydes and alcohols. MIL-101Cr-NO2 obtained by direct reaction between CrO3 and 2-nitro-terephthalate showed the highest activity with 99% conversion in the B-M reaction in 90 min and turnover numbers of 114. The activity decreased in the order MIL-101Cr-NO2 > MIL-101Cr > MIL-101Cr-NH2. Within different samples of nonfunctionalized MIL-101Cr the activity increased with surface area. Methanol gas sorption of the different MIL materials correlates with the BET surface area and pore volume but not with the diacetalization activity. Benzaldehyde adsorption from heptane showed no significant difference for the different MILs. Gas sorption studies of CD3CN to probe for a higher Lewis acidity in MIL-101Cr-NO2 remained inconclusive. A high B-M catalytic activity of wet MIL-101Cr-NO2 excluded significant contributions from coordinatively unsaturated Lewis-acid sites. pH measurements of methanol dispersions of the MIL materials gave the most acidic pH (as low as 1.9) for MIL-101Cr-NO2, which significantly increased over MIL-101Cr (3.0) to MIL-101Cr-NH2 (3.3). The increase in acidity is of short range or a surface effect to the heterogeneous MIL particles as protons dissociating from the polarized aqua ligands (Cr-OH2) have to stay near the insoluble counteranionic framework. The variation in Brønsted acidity of MIL-101Cr-NO2 > MIL-101Cr ≈ MIL-101Cr-NH2 correlates with the withdrawing effect of NO2 and the diacetalization activity. The catalytic B-M activity of soluble, substitution-inert, and acidic Cr(NO3)3·9H2O supports the Brønsted-acid effect of the MIL materials. Filtration and centrifugation experiments with MIL-101Cr-NO2 revealed that about 2/3 of the catalytic activity comes from nano-MOF particles with a diameter below 200 nm. The MIL

Aerosol simulation including chemical and nuclear reactions

International Nuclear Information System (INIS)

Marwil, E.S.; Lemmon, E.C.

1985-01-01

The numerical simulation of aerosol transport, including the effects of chemical and nuclear reactions presents a challenging dynamic accounting problem. Particles of different sizes agglomerate and settle out due to various mechanisms, such as diffusion, diffusiophoresis, thermophoresis, gravitational settling, turbulent acceleration, and centrifugal acceleration. Particles also change size, due to the condensation and evaporation of materials on the particle. Heterogeneous chemical reactions occur at the interface between a particle and the suspending medium, or a surface and the gas in the aerosol. Homogeneous chemical reactions occur within the aersol suspending medium, within a particle, and on a surface. These reactions may include a phase change. Nuclear reactions occur in all locations. These spontaneous transmutations from one element form to another occur at greatly varying rates and may result in phase or chemical changes which complicate the accounting process. This paper presents an approach for inclusion of these effects on the transport of aerosols. The accounting system is very complex and results in a large set of stiff ordinary differential equations (ODEs). The techniques for numerical solution of these ODEs require special attention to achieve their solution in an efficient and affordable manner. 4 refs

Catalytic performance of heterogeneous Rh/C3N4 for the carbonylation of methanol

Science.gov (United States)

Budiman, Anatta Wahyu; Choi, Myoung Jae; Nur, Adrian

2018-02-01

The excess of water in homogeneous the carbonylation of methanol system could increase the amount of by-products formed through water-gas shift reaction and could accelerate the rusting of equipment. Many scientists tried to decrease the content of water in the carbonylation of methanol system by using lithium and iodide promoter that results a moderate catalytic activity in the water content at 2wt%. The heterogenized catalyst offers several distinct advantages such as it was enables increased catalyst concentration in the reaction mixture, which is directly proportional to acetic acid production rate, without the addition of an alkali iodide salt promoter. The heterogeneous catalyst also results in reduced by-product formation. This study is aimed to produce a novel catalyst (Rh/C3N4) with a high selectivity of acetic acid in a relatively lower water and halide content. This novel catalyst performs high conversion and selectivity of acetic acid as the result of the strong ionic bonding of melamine and rhodium complex species that was caused by the presence of methyl iodide species. The CO2 in feed gas significantly decreases the catalytic activity of Rh-melamine because of its inert characteristics. The kinetic test was performed as that the first order kinetic equation. The kinetic tests revealed the reaction route of the the carbonylation of methanol in this system was performed trough the methyl acetate.

A Copper(II)-Paddlewheel Metal-Organic Framework with Exceptional Hydrolytic Stability and Selective Adsorption and Detection Ability of Aniline in Water.

Science.gov (United States)

Chen, Ya; Wang, Bin; Wang, Xiaoqing; Xie, Lin-Hua; Li, Jinping; Xie, Yabo; Li, Jian-Rong

2017-08-16

Copper(II)-paddlewheel-based metal-organic frameworks (CP-MOFs) represent a unique subclass of MOFs with highly predictable porous structures, facile syntheses, and functional open metal sites. However, the lack of high hydrolytic stability is an obstacle for CP-MOFs in many practical applications. In this work, we report a new CP-MOF, [Cu 4 (tdhb)] (BUT-155), which is constructed from a judiciously designed carboxylate ligand with high coordination connectivity (octatopic), abundant hydrophobic substituents (six methyl groups), and substituent constrained geometry (tetrahedral backbone), tdhb 8- [H 8 tdhb = 3,3',5,5'-tetrakis(3,5-dicarboxyphenyl)-2,2',4,4',6,6'-hexamethylbiphenyl)]. BUT-155 shows high porosity with a Brunauer-Emmett-Teller surface area of 2070 m 2 /g. Quite interestingly, this CP-MOF retains its structural integrity after being treated in water for 10 days at room temperature or in boiling water for 24 h. To the best of our knowledge, BUT-155 represents the first CP-MOF that is demonstrated to retain its structural integrity in boiling water. The high hydrolytic stability of BUT-155 allowed us to carry out adsorption studies of water vapor and aqueous organic pollutants on it. Water-vapor adsorption reveals a sigmoidal isotherm and a high uptake (46.7 wt %), which is highly reversible and regenerable. In addition, because of the availability of soft-acid-type open Cu(II) sites, BUT-155 shows a high performance for selective adsorption of soft-base-type aniline over water or phenol, and a naked-eye detectable color change for the MOF sample accompanies this. The adsorption selectivity and high adsorption capacity of aniline in BUT-155 are also well-interpreted by single-crystal structures of the water- and aniline-included phases of BUT-155.

Development of Conductivity Method as an Alternative to Titration for Hydrolytic Resistance Testing Used for Evaluation of Glass Vials Used in Pharmaceutical Industry.

Science.gov (United States)

Fujimori, Kiyoshi; Lee, Hans; Phillips, Joseph; Nashed-Samuel, Yasser

The European Pharmacopeia surface test to analyze the hydrolytic resistance is a common industrial method to understand and ensure the quality of produced glass vials. Hydrolytic resistance is evaluated by calculating the alkalinity of water extract from autoclaved vials by titration. As an alternative to this titration technique, a conductivity technique was assessed, which directly measures the ions in the water extract. A conductivity meter with a 12 mm diameter electrode was calibrated with a 100 μS/cm conductivity standard and carryover minimized by rinsing the probe in a water beaker per analysis. The limit of quantification at 1 μS/cm was determined as having a signal-to-noise ratio of 3 compared with the water blank. The conductivity method was selective for glass-composing elements (boron, sodium, aluminum, silicon, potassium, and calcium) within the vial extract. Accuracies of spiked conductivity standard within the range of 1 to 100 μS/cm were ±7% and had linearity with coefficient of determination (R 2 ) of ≥0.9999. Intraday precision had a relative standard deviation (RSD) (n = 5) of ≤6% for spiked conductivity standard within the range of 1 to 100 μS/cm. Interday precision had a RSD (n = 4) of ≤6% for 10 vials from three glass vial lots. Conductivity of water extracts from nine sets of seven lots of glass vials had a precise linear relationship [R 2 = 0.9876, RSD = 1% (n = 9)] with titration volumes of the same lots. Conductivity results in μS/cm could be converted to titration volumes in milliliters by a conversion factor of 0.0275. The simplicity, sample stability, and individual vial analysis of the conductivity technique were more advantageous than the current titration technique. The quality of glass vials used as primary containers in the pharmaceutical industry is of concern due to recent observations of glass flake-like delamination, or lamellae, under specific storage conditions. The current European Pharmacopoeia method to assess

Validation of an experimental setup to study atmospheric heterogeneous ozonolysis of semi-volatile organic compounds

Directory of Open Access Journals (Sweden)

M. Pflieger

2009-03-01

Full Text Available There is currently a need for reliable experimental procedures to follow the heterogeneous processing simulating the atmospheric conditions. This work offers an alternative experimental device to study the behaviour of semi-volatile organic compounds (SVOC that presumably exhibit extremely slow reactivity (e.g. pesticides towards the atmospheric oxidants such as ozone and OH. Naphthalene was chosen as a test compound since it was widely studied in the past and hence represents a good reference. Prior to ozone exposure, the gaseous naphthalene was adsorbed via gas-solid equilibrium on silica and XAD-4 particles. Then, the heterogeneous reaction of ozone with adsorbed naphthalene was investigated in specially designed flow tube reactors. After the reaction, the remaining naphthalene (adsorbed on particles surface was extracted, filtered and analyzed by Gas Chromatography-Flame Ionization Detector (GC-FID. Thus, the kinetics results were obtained following the consumption of naphthalene. Using this procedure, the rate constants of heterogeneous ozonolysis of naphthalene (k_O3 silica=2.26 (±0.09×10⁻¹⁷ cm³ molec⁻¹ s⁻¹ and k_O3 XAD-4=4.29 (±1.06×10⁻¹⁹ cm³ molec⁻¹ s⁻¹ were determined for silica and XAD-4 particles, at 25°C and relative humidity <0.7%. The results show that the nature of the particles significantly affects the kinetics and that heterogeneous ozonolysis of naphthalene is faster than its homogeneous ozonolysis in the gas phase.

Peculiarities of heterogeneous radiolysis of carbon dioxide in the presence of aluminium oxide

International Nuclear Information System (INIS)

Rustamov, V.R.; Kurbanov, M.A.; Kerimov, V.K.; Musaeva, P.F.

1982-01-01

The effect of ν-radiation dose rate, reaction temperature and treatment of aluminium oxide on the yield of CO at radiolysis of CO 2 /ν-Al 2 O 3 heterogeneous system has been investigated. The measurements have been carried out at 0.55 and 5.5 Gr/s dose rates in 40-300 deg C temperature range. Kinetic curves of CO accumulation are characterized by the saturation region at 0.15-0.2 MG 2 doses. In such a way, the dependence of CO yeild on the dose attests that the reaction of radiation annealing of defects occurs in Al 2 O 3 and that decreases the efficiency of CO 2 decomposition. The rise of temperature from 40 to 300 deg results in the decrease of CO 2 yield and in 100-200 range it is manifested more markedly. This fact is conditioned by the increase of reaction rates leading to the decrease of CO 2 decomposition rate as the temperature rises. The reaction mechanism is discussed

Rat lingual lipase: partial purification, hydrolytic properties, and comparison with pancreatic lipase.

Science.gov (United States)

Roberts, I M; Montgomery, R K; Carey, M C

1984-10-01

We have partially purified lingual lipase from the serous glands of rat tongue. With a combination of Triton X-100 extraction or Triton X-114 phase-separation techniques, Bio-Bead SM-2 treatment, dialysis, and gel filtration on Sephadex G-200 or Sephacryl S-300, we obtained a sparingly soluble lipid-free protein demonstrating hydrolytic activity against triglycerides and negligible phospholipase or cholesteryl esterase activities. Compared with homogenate, specific activities of the enzyme were enriched 3- to 5-fold prior to gel filtration and 10-fold after gel filtration. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration under denaturing conditions (6 M guanidine X HCl or 0.1% sodium dodecyl sulfate) revealed one major glycoprotein band with Mr approximately 50,000. Gel filtration of the active enzyme in 0.1% Triton X-100 gave an Mr approximately 270,000-300,000, suggesting extensive self-aggregation. With both tributyrin and triolein, the pH optimum of the purified enzyme was 4.0 and activity extended from pH 2.0 to 8.0. In contrast to purified human pancreatic lipase, lingual lipase hydrolyzed triglyceride emulsions and mixed micelles stabilized with both short-chain (dihexanoyl) and long-chain (egg) lecithin and were inhibited only slightly (18-25%) by micellar concentrations of two common bile salts, taurodeoxycholate and taurocholate. Our results suggest that the hydrolysis of dietary fat by lingual lipase may extend from the pharynx through the esophagus and stomach and into the upper small intestine.

Synergistic rate boosting of collagen fibrillogenesis in heterogeneous mixtures of crowding agents.

Science.gov (United States)

Dewavrin, Jean-Yves; Abdurrahiem, Muhammed; Blocki, Anna; Musib, Mrinal; Piazza, Francesco; Raghunath, Michael

2015-03-26

The competition for access to space that arises between macromolecules is the basis of the macromolecular crowding phenomenon, known to modulate biochemical reactions in subtle ways. Crowding is a highly conserved physiological condition in and around cells in metazoans, and originates from a mixture of heterogeneous biomolecules. Here, using collagen fibrillogenesis as an experimental test platform and ideas from the theory of nonideal solutions, we show that an entropy-based synergy is created by a mixture of two different populations of artificial crowders, providing small crowders with extra volume occupancy when in the vicinity of bigger crowders. We present the physiological mechanism by which synergistic effects maximize volume exclusion with the minimum amount of heterogeneous crowders, demonstrating how the evolutionarily optimized crowded conditions found in vivo can be reproduced effectively in vitro.

Production of hydrolytic enzymes by Trichoderma isolates with antagonistic activity against Crinipellis perniciosa, the causal agent of witches' broom of cocoa

Directory of Open Access Journals (Sweden)

Marco Janice Lisboa De

2003-01-01

Full Text Available Two isolates of Trichoderma, which reduce the incidence of witches'broom disease caused in cocoa by Crinipellis perniciosa, were evaluated for their potential to produce hydrolases in liquid medium. Very low or no hydrolytic activity was produced in the absence of any substrate. The activities of chitinase, N-acetylglucosaminidase, beta-1,3-glucanase, total cellulase, endoglucanase, aryl- beta-glucosidase, beta-glucosidase, protease and amylase increased dramatically within 72-120 h of growth in the presence of specific substrates. Except for N-acetylglucosaminidase and beta-glucosidase Trichoderma harzianum isolate 1051 produced the largest amounts of hydrolases. The possible involvement of these enzymes in the antagonistic interaction between Trichoderma and C. perniciosa is discussed.

High-throughput heterogeneous catalyst research

Science.gov (United States)

Turner, Howard W.; Volpe, Anthony F., Jr.; Weinberg, W. H.

2009-06-01

With the discovery of abundant and low cost crude oil in the early 1900's came the need to create efficient conversion processes to produce low cost fuels and basic chemicals. Enormous investment over the last century has led to the development of a set of highly efficient catalytic processes which define the modern oil refinery and which produce most of the raw materials and fuels used in modern society. Process evolution and development has led to a refining infrastructure that is both dominated and enabled by modern heterogeneous catalyst technologies. Refineries and chemical manufacturers are currently under intense pressure to improve efficiency, adapt to increasingly disadvantaged feedstocks including biomass, lower their environmental footprint, and continue to deliver their products at low cost. This pressure creates a demand for new and more robust catalyst systems and processes that can accommodate them. Traditional methods of catalyst synthesis and testing are slow and inefficient, particularly in heterogeneous systems where the structure of the active sites is typically complex and the reaction mechanism is at best ill-defined. While theoretical modeling and a growing understanding of fundamental surface science help guide the chemist in designing and synthesizing targets, even in the most well understood areas of catalysis, the parameter space that one needs to explore experimentally is vast. The result is that the chemist using traditional methods must navigate a complex and unpredictable diversity space with a limited data set to make discoveries or to optimize known systems. We describe here a mature set of synthesis and screening technologies that together form a workflow that breaks this traditional paradigm and allows for rapid and efficient heterogeneous catalyst discovery and optimization. We exemplify the power of these new technologies by describing their use in the development and commercialization of a novel catalyst for the

Structure-activity relationships of heterogeneous catalysts from time-resolved X-ray absorption spectroscopy

International Nuclear Information System (INIS)

Ressler, T.; Jentoft, R.E.; Wienold, J.; Girgsdies, F.; Neisius, T.; Timpe, O.

2003-01-01

Knowing the composition and the evolution of the bulk structure of a heterogeneous catalyst under working conditions (in situ) is a pre-requisite for understanding structure-activity relationships. X-ray absorption spectroscopy can be employed to study a catalytically active material in situ. In addition to steady-state investigations, the technique permits experiments with a time-resolution in the sub-second range to elucidate the solid-state kinetics of the reactions involved. Combined with mass spectrometry, the evolution of the short-range order structure of a heterogeneous catalyst, the average valence of the constituent metals, and the phase composition can be obtained. Here we present results obtained from time-resolved studies on the reduction of MoO 3 in propene and in propene and oxygen

ISHHC XIII International Symposium on the Relations betweenHomogeneous and Heterogeneous Catalysis

Energy Technology Data Exchange (ETDEWEB)

Somorjai (Ed.), G.A.

2007-06-11

The International Symposium on Relations between Homogeneous and Heterogeneous Catalysis (ISHHC) has a long and distinguished history. Since 1974, in Brussels, this event has been held in Lyon, France (1977), Groeningen, The Netherlands (1981); Asilomar, California (1983); Novosibirsk, Russia (1986); Pisa, Italy (1989); Tokyo, Japan (1992); Balatonfuered, Hungary (1995); Southampton, United Kingdom (1999); Lyon, France (2001); Evanston, Illinois (2001) and Florence, Italy (2005). The aim of this international conference in Berkeley is to bring together practitioners in the three fields of catalysis, heterogeneous, homogeneous and enzyme, which utilize mostly nanosize particles. Recent advances in instrumentation, synthesis and reaction studies permit the nanoscale characterization of the catalyst systems, often for the same reaction, under similar experimental conditions. It is hoped that this circumstance will permit the development of correlations of these three different fields of catalysis on the molecular level. To further this goal we aim to uncover and focus on common concepts that emerge from nanoscale studies of structures and dynamics of the three types of catalysts. Another area of focus that will be addressed is the impact on and correlation of nanosciences with catalysis. There is information on the electronic and atomic structures of nanoparticles and their dynamics that should have importance in catalyst design and catalytic activity and selectivity.

Kinetic Study on the Esterification of Palm Fatty Acid Distillate (PFAD) Using Heterogeneous Catalyst

Science.gov (United States)

Rofiqah, U.; Djalal, R. A.; Sutrisno, B.; Hidayat, A.

2018-05-01

Esterification with heterogeneous catalysts is believed to have advantages compared to homogeneous catalysts. Palm Fatty Acid Distillate (PFAD) was esterified by ZrO2 -SO4 2-/natural zeolite at temperature variation of 55°C, 60°C, and 65°C to produce biodiesel. Determination of reaction kinetics was done by experiment and modeling. Kinetic study was approached using pseudo-homogeneous model of first order. For experiment, reaction kinetics were 0.0031 s-1, 0.0054 s-1, and 0.00937 s-1 for a temperature of 55 °C, 60 °C and 65 °C, respectively. For modelling, reaction kinetics were 0.0030 s-1, 0.0055 s-1, and 0.0090 s-1 for a temperature of 55°C, 60°C and 65°C, respectively. Rate and conversion of reaction are getting increased by increasing temperature.

Challenges in the Greener Production of Formates/Formic Acid, Methanol, and DME by Heterogeneously Catalyzed CO2 Hydrogenation Processes

KAUST Repository

Á lvarez, Andrea; Bansode, Atul; Urakawa, Atsushi; Bavykina, Anastasiya V.; Wezendonk, Tim A.; Makkee, Michiel; Gascon, Jorge; Kapteijn, Freek

2017-01-01

carefully summarize the state of the art in the development of heterogeneous catalysts for these important hydrogenation reactions. Finally, in an attempt to give an order of magnitude regarding CO2 valorization, we critically assess economical aspects

Heterogeneous base-catalyzed methanolysis of vegetable oils: State of art

Directory of Open Access Journals (Sweden)

Miladinović Marija R.

2010-01-01

Full Text Available Today, homogeneous base-catalyzed methanolysis is most frequently used method for industrial biodiesel production. High requirements for the quality of feedstocks and the problems related to a huge amount of wastewaters have led to the development of novel biodiesel production technologies. Among them, the most important is heterogeneous base-catalyzed methanolysis, which has been intensively investigated in the last decade in order to develop new catalytic systems, to optimize the reaction conditions and to recycle catalysts. These studies are a base for developing continuous biodiesel production on industrial scale in near future. The present work summarizes up-to-date studies on biodiesel production by heterogeneous base-catalyzed methanolysis. The main goals were to point out the application of different base compounds as catalysts, the methods of catalyst preparation, impregnation on carriers and recycling as well as the possibilities to improve existing base-catalyzed biodiesel production processes and to develop novel ones.

Heterogeneous cellular networks

CERN Document Server

Hu, Rose Qingyang

2013-01-01

A timely publication providing coverage of radio resource management, mobility management and standardization in heterogeneous cellular networks The topic of heterogeneous cellular networks has gained momentum in industry and the research community, attracting the attention of standardization bodies such as 3GPP LTE and IEEE 802.16j, whose objectives are looking into increasing the capacity and coverage of the cellular networks. This book focuses on recent progresses,  covering the related topics including scenarios of heterogeneous network deployment, interference management i

Comparison of techniques for the determination of conversion during suspension polymerization reactions

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J. C. Santos

2008-06-01

Full Text Available The determination of conversion during suspension polymerization reactions is not an easy task due to the heterogeneity of the reaction medium and the tendency of particles to agglomerate rapidly when stirring is stopped. Usually, bulk polymerization in ampoules is employed to study the kinetics of suspension polymerization reactions. In this work, a comparison of different techniques for the determination of conversion during suspension polymerization reactions is presented. Results showed a good agreement between the conversion obtained by gravimetry during styrene suspension polymerization and on-line conversion monitoring data using fiber-optic based Raman Spectroscopy. Nevertheless, the polymerization rate of styrene bulk polymerization carried out in ampoules was higher than the real reaction rate of styrene suspension polymerization due to slightly higher reaction temperatures. Simulation results using the experimental temperature data in a mathematical model confirmed these results.

Evidence for the Active Phase of Heterogeneous Catalysts through In Situ Reaction Product Imaging and Multiscale Modeling

Energy Technology Data Exchange (ETDEWEB)

Matera, S.; Blomberg, S.; Hoffmann, M. J.; Zetterberg, J.; Gustafson, J.; Lundgren, E.; Reuter, K.

2015-06-17

We use multiscale modeling to analyze laser-induced fluorescence (LIF) measurements of the CO oxidation reaction over Pd(100) at near-ambient reaction conditions. Integrating density functional theory-based kinetic Monte Carlo simulations of the active catalyst into fluid-dynamical simulations of the mass transport inside the reactor chamber, we calculate the reaction product concentration directly above the catalyst surface. Comparing corresponding data calculated for different surface models against the measured LIF signals, we can discriminate the one that predominantly actuates the experimentally measured catalytic activity. For the probed CO oxidation reaction conditions, the experimental activity is due to pristine Pd(100) possibly coexisting with other (oxidic) domains on the surface.

Shock interactions with heterogeneous energetic materials

Science.gov (United States)

Yarrington, Cole D.; Wixom, Ryan R.; Damm, David L.

2018-03-01

The complex physical phenomenon of shock wave interaction with material heterogeneities has significant importance and nevertheless remains little understood. In many materials, the observed macroscale response to shock loading is governed by characteristics of the microstructure. Yet, the majority of computational studies aimed at predicting phenomena affected by these processes, such as the initiation and propagation of detonation waves in explosives or shock propagation in geological materials, employ continuum material and reactive burn model treatment. In an effort to highlight the grain-scale processes that underlie the observable effects in an energetic system, a grain-scale model for hexanitrostilbene (HNS) has been developed. The measured microstructures were used to produce synthetic computational representations of the pore structure, and a density functional theory molecular dynamics derived equation of state (EOS) was used for the fully dense HNS matrix. The explicit inclusion of the microstructure along with a fully dense EOS resulted in close agreement with historical shock compression experiments. More recent experiments on the dynamic reaction threshold were also reproduced by inclusion of a global kinetics model. The complete model was shown to reproduce accurately the expected response of this heterogeneous material to shock loading. Mesoscale simulations were shown to provide a clear insight into the nature of threshold behavior and are a way to understand complex physical phenomena.

A heterogeneous Pd-Bi/C catalyst in the synthesis of L-lyxose and L-ribose from naturally occurring D-sugars.

Science.gov (United States)

Fan, Ao; Jaenicke, Stephan; Chuah, Gaik-Khuan

2011-10-26

A critical step in the synthesis of the rare sugars, L-lyxose and L-ribose, from the corresponding D-sugars is the oxidation to the lactone. Instead of conventional oxidizing agents like bromine or pyridinium dichromate, it was found that a heterogeneous catalyst, Pd-Bi/C, could be used for the direct oxidation with molecular oxygen. The composition of the catalyst was optimized and the best results were obtained with 5 : 1 atomic ratio of Pd : Bi. The overall yields of the five-step procedure to L-ribose and L-lyxose were 47% and 50%, respectively. The synthetic procedure is advantageous from the viewpoint of overall yield, reduced number of steps, and mild reaction conditions. Furthermore, the heterogeneous oxidation catalyst can be easily separated from the reaction mixture and reused with no loss of activity.

Amino-functionalized metal-organic frameworks as tunable heterogeneous basic catalysts

Energy Technology Data Exchange (ETDEWEB)

Fischer, M.; Hartmann, M. [Erlangen-Nuernberg Univ., Erlangen (Germany). Erlangen Catalysis Resource Center

2011-07-01

Metal-organic framework (MOF) materials have been explored for applications in heterogeneous catalysis in recent years. In addition to the use of MOFs as supports for the deposition of highly dispersed metal particles, the incorporation of active centers such as coordinatively unsaturated metal sites and the functionalization of the organic linkers with acidic or basic groups seems to be most promising. In our contribution, three different MOFs carrying amino groups at their organic linkers, namely Fe-MIL-101-NH{sub 2} (S{sub BET} = 3438 m{sup 2}g{sup -1}), Al-MIL-101-NH{sub 2} (S{sub BET} = 3099 m{sup 2}g{sup -1}) and CAU-1 (S{sub BET} = 1492 m{sup 2}g{sup -1}), were synthesized and tested in the Knoevenagel condensation of benzaldehyde with malononitrile and with ethyl cyanoacetate, respectively. It is shown that the expected products benzylidenemalononitrile (BzMN) and ethyl a-cyanocinnamate (EtCC) are formed with selectivities of more than 99 % and yields of 90 to 95 % after 3 h (for BzMN). Due to the very small pore windows of CAU-1 (0.3 to 0.4 nm) the reaction proceeds much slower over this catalyst in comparison to the amino-MIL-101 derivatives, which possess open pore windows of up to 1.6 nm. Finally, leaching tests confirm that the reaction is heterogeneously catalyzed. Moreover, the catalysts are recyclable without significant loss of activity. (orig.)

Cation dependency of the hydrolytic activity of activated bovine Protein C

International Nuclear Information System (INIS)

Hill, K.A.W.

1986-01-01

The hydrolytic activity of activated bovine plasma Protein C (APC) is dependent upon monovalent or divalent cations. The kinetics of APC activity were examined with a variety of monovalent and divalent cations, and significant differences were observed. Similar studies were performed with des(1-41, light chain)APC (GDAPC), from which all γ-carboxyglutamic acid residues have been removed. These studies provided useful information concerning the cation dependency. Divalent cations apparently stimulate APC and GDAPC kinetic activity through association at a single γ-carboxyglutamic acid-independent high affinity binding site. A Mn(II) binding site of this nature of GDAPC was determined by EPR spectroscopy, to possess a dissociation constant of 53 +/- 8 uM. Monovalent cations stimulate GDAPC activity through association at an apparently single binding site that is distinct from the divalent cation site. The monovalent cation , Tl(I), was determined, by 205 Tl(I) NMR spectroscopy, to bind to APC and GDAPC with dissociation constants of 16 +/- 8 mM and 32+/- 11 mM, respectively. Both NMR and EPR spectroscopy have been utilized to estimate topographical relationships between divalent cation sites, monovalent cation sites, and the active site of GDAPC. By observing the paramagnetic effects of either Mn(II) or an active site directed spin-label on the longitudinal relaxation rates of Tl(I) nuclei bound to this enzyme, the average interatomic distance between Mn(II) and Tl(I) was calculated to be 8.3 +/- 0.3 A, and the average distance between Tl(I) and the spin-label free electron was estimated to be 3.8 +/- 0.2 A

Homogenization methods for heterogeneous assemblies

International Nuclear Information System (INIS)

Wagner, M.R.

1980-01-01

The third session of the IAEA Technical Committee Meeting is concerned with the problem of homogenization of heterogeneous assemblies. Six papers will be presented on the theory of homogenization and on practical procedures for deriving homogenized group cross sections and diffusion coefficients. That the problem of finding so-called ''equivalent'' diffusion theory parameters for the use in global reactor calculations is of great practical importance. In spite of this, it is fair to say that the present state of the theory of second homogenization is far from being satisfactory. In fact, there is not even a uniquely accepted approach to the problem of deriving equivalent group diffusion parameters. Common agreement exists only about the fact that the conventional flux-weighting technique provides only a first approximation, which might lead to acceptable results in certain cases, but certainly does not guarantee the basic requirement of conservation of reaction rates

Hydrogenation of citral into its derivatives using heterogeneous catalyst

Science.gov (United States)

Sudiyarmanto, Hidayati, Luthfiana Nurul; Kristiani, Anis; Aulia, Fauzan

2017-11-01

Citral as known as a monoterpene can be found in plants and citrus fruits. The hydrogenation of citral into its derivatives become interesting area for scientist. This compound and its derivatives can be used for many application in pharmaceuticals and food areas. The development of heterogeneous catalysts become an important aspect in catalytic hydrogenation citral process. Nickel supported catalysts are well known as hydrogenation catalyst. These heterogeneous catalysts were tested their catalytic activity in hydrogenation of citral. The effect of various operation conditions, in term of feed concentration, catalyst loading, temperature, and reaction time were also studied. The liquid products produced were analyzed by using Gas Chromatography-Mass Spectroscopy (GC-MS). The result of catalytic activity tests showed nickel skeletal catalyst exhibits best catalytic activity in hydrogenation of citral. The optimum of operation condition was achieved in citral concentration 0.1 M with nickel skeletal catalyst loading of 10% (w/w) at 80 °C and 20 bar for 2 hours produced the highest conversion as of 64.20% and the dominant product resulted was citronellal as of 56.48%.

Porous Materials for Hydrolytic Dehydrogenation of Ammonia Borane

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Tetsuo Umegaki

2015-07-01

Full Text Available Hydrogen storage is still one of the most significant issues hindering the development of a “hydrogen energy economy”. Ammonia borane is notable for its high hydrogen densities. For the material, one of the main challenges is to release efficiently the maximum amount of the stored hydrogen. Hydrolysis reaction is a promising process by which hydrogen can be easily generated from this compound. High purity hydrogen from this compound can be evolved in the presence of solid acid or metal based catalyst. The reaction performance depends on the morphology and/or structure of these materials. In this review, we survey the research on nanostructured materials, especially porous materials for hydrogen generation from hydrolysis of ammonia borane.

Porous Materials for Hydrolytic Dehydrogenation of Ammonia Borane.

Science.gov (United States)

Umegaki, Tetsuo; Xu, Qiang; Kojima, Yoshiyuki

2015-07-21

Hydrogen storage is still one of the most significant issues hindering the development of a "hydrogen energy economy". Ammonia borane is notable for its high hydrogen densities. For the material, one of the main challenges is to release efficiently the maximum amount of the stored hydrogen. Hydrolysis reaction is a promising process by which hydrogen can be easily generated from this compound. High purity hydrogen from this compound can be evolved in the presence of solid acid or metal based catalyst. The reaction performance depends on the morphology and/or structure of these materials. In this review, we survey the research on nanostructured materials, especially porous materials for hydrogen generation from hydrolysis of ammonia borane.

Synthesis and Reactions of Five-Membered Heterocycles Using Phase Transfer Catalyst (PTC Techniques

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Ahmed M. El-Sayed

2014-01-01

Full Text Available Phase transfer catalysts (PTCs have been widely used for the synthesis of organic compounds particularly in both liquid-liquid and solid-liquid heterogeneous reaction mixtures. They are known to accelerate reaction rates by facilitating formation of interphase transfer of species and making reactions between reagents in two immiscible phases possible. Application of PTC instead of traditional technologies for industrial processes of organic synthesis provides substantial benefits for the environment. On the basis of numerous reports it is evident that phase-transfer catalysis is the most efficient way for generation and reactions of many active intermediates. In this review we report various uses of PTC in syntheses and reactions of five-membered heterocycles compounds and their multifused rings.

Recent advances in heterogeneous catalytic conversion of glucose to 5-hydroxymethylfurfural via green routes

KAUST Repository

Wang, Jianjian

2017-05-12

With concerns of diminishing fossil fuel reserves and environmental deterioration, great efforts have been made to explore novel approaches of efficiently utilizing bio-renewable feedstocks to produce chemicals and fuels. 5-Hydroxymethylfurfural (HMF), generated from dehydration of six-carbon ketose, is regarded as a primary and versatile renewable building block to realize the goal of production of these high valued products from renewable biomass resources transformation. In this review, we summarize the recent advances via green routes in the heterogeneous reaction system for the catalytic production of HMF from glucose conversion, and emphasize reaction pathways of these reaction approaches based on the fundamental mechanistic chemistry as well as highlight the challenges (such as separation and purification of products, reusing and regeneration of catalyst, recycling solvent) in this field.

Studies of Heterogenous Palladium and Related Catalysts for Aerobic Oxidation of Primary Alcohols

Science.gov (United States)

Ahmed, Maaz S.

alcohol solvent and the surface of the catalyst: (listed in order of strength) lone pair-surface (heterocyclic primary alcohols) > pi-surface (aryl primary alcohols) > van der Waals-surface (alkyl primary alcohols). These interactions were previously underappreciated in condensed phase heterogeneously catalyzed aerobic oxidations. Bi and Te serve as synergistic promoters that enhance both the rate and yield of the reactions relative to reactions employing Pd alone or Pd in combination with Bi or with Te as the sole promoter. We report X-ray absorption spectroscopic studies of the heterogenous catalyst. These methods show that the promoters undergo oxidation in preference to Pd, maintaining the Pd surface in the active metallic state and preventing inhibition by surface Pd-oxide formation. The data also suggest formation of a Pd-Te alloy phase that modifies the electronic properties of the Pd catalyst. Collectively, these results provide valuable insights into the synergistic benefits of multiple promoters in heterogeneous catalytic oxidation reactions.

Hydrolytic stability of three-step etch-and-rinse adhesives in occlusal class-I cavities.

Science.gov (United States)

De Munck, Jan; Mine, Atsushi; Vivan Cardoso, Marcio; Van Landuyt, Kirsten L; Lührs, Anne-Katrin; Poitevin, André; Hanabusa, Masao; Kuboki, Takuo; Van Meerbeek, Bart

2013-11-01

A dental adhesive without small and hydrophilic monomers such as 2-hydroxyethyl methacrylate (HEMA) and triethylene glycol dimethacrylate (TEGDMA) would be beneficial in order to avoid contact allergies. However, these monomers are important to increase infiltration and polymerization of the adhesive. Therefore, the purpose of this study was to evaluate the bonding effectiveness and bond durability of a more hydrophobic and biocompatible adhesive as compared to a conventional three-step etch-and-rinse adhesive. Sixteen non-carious human third molars were used to determine the micro-tensile bond strength testing (μTBS) and interfacial ultrastructure by transmission electron microscopy (TEM) of the more hydrophobic cmf adhesive system (Saremco) adhesive as compared to the control OptiBond FL (Kerr). The more hydrophobic and biocompatible three-step etch-and-rinse adhesive was able to produce a reasonable short-time bonding effectiveness. In the long term, the collagen fibrils in the hybrid layer were not effectively protected and were prone to hydrolytic degradation. As a result, long-term bonding effectiveness of this novel adhesive was very low. Application of a more hydrophobic adhesive without altering the application procedure considerably results in a reduced durability of the created bond Omitting small and hydrophilic components from the adhesive formulation may impair the durability of your composite restoration.

Effect of catalysts on heterogeneous oxidation of coal

Energy Technology Data Exchange (ETDEWEB)

Glazkova, A P; Kazarova, Yu A; Suslov, A V

1978-01-01

Analyzes the effects of catalysts on the heterogeneous oxidation of coal in deflagration processes of stoichiometric mixtures. The following substances are studied as catalysts: alkali and alkaline-earth metals, and compounds of copper, lead, chromium, iron, and sulfur. In the first case the catalysts are used in the form of nitrates and the nitrate simultaneously plays the role of an oxidizer. In the second case the catalysts are added to stoichiometric mixtures of ammonium nitrate with carbon. It is shown that during carbon oxidation by nitrates the catalytic efficiency of the metals studied forms the following order: sodium > lead > potassium > barium > aluminium > calcium > magnesium > copper. The calculated and experimental parameters of combustion are given. The problem of dependence of combustion rate on combustion heat, the mechanism of the combustion reaction and the catalytic effects of the additives are discussed. Features of heterogeneous catalysis in the oxidation process of carbon by various oxidizers are analyzed. The investigations on the combustion process are important as the process takes place during explosion of coal dust in underground coal mines and during burning of coal in industrial furnaces. (34 refs.) (In Russian)

Control rod effects on reaction rate distributions in tight pitched PuO2-UO2 fuel assembly

International Nuclear Information System (INIS)

Gil, Choong-Sup; Okumura, Keisuke; Ishiguro, Yukio

1991-11-01

Investigations were made for the heterogeneity effects caused by insertion or withdrawal of a B 4 C control rod on fine structure of reaction rates distributions in a tight pitched PuO 2 -UO 2 fuel assembly. Analysis was carried out by using the VIM and SRAC codes with the libraries based on JENDL-2 for the hexagonal fuel assembly basically corresponding to the PROTEUS-LWHCR experimental core. The reaction rates are affected more remarkably by the withdrawal of the control rod rather than its insertion. The changes of the reaction rates were decomposed into three terms of spectrum shifts, the changes of effective cross sections with fine groups, and their higher order components. From the analysis, it is concluded that most changes of reaction rates are caused by spectral shifts. The SRAC code with fine group constants can predict the distribution of reaction rates and their ratios with the accuracy of about 5 % except for the values related to Pu-242 capture rate, as compared with the VIM results. To increase the accuracy, it is necessary to generate the effective cross sections of the fuel near control rods with consideration of the heterogeneities in the fuel assembly. (author)

Investigation into reaction of heterogenous isotopic exchange with gaseoUs tritium in solution for preparation labelled lipid compounds

International Nuclear Information System (INIS)

Shevchenko, V.P.; Myasoedov, N.F.

1983-01-01

The applicability of the method of heterogeneous catalytic isotopic exchange with gaseous tritium in the solution for the production of labelled lipide preparations is studied. Labelled saturated and unsaturated aliphatic acids, prostaglandins, phospholipides and sphingolipides are prepared

EFFECT OF THE REACTION CONDITIONS OVER THE YIELD AND PROPERTIES OF METHYLCELLULOSE OBTAINED FROM PINUS RADIATA KRAFT BLEACHED CELLULOSE

OpenAIRE

TAPIA, C.; SAPAG-HAGAR, J.; ANDRADE, C.T.; HASSÓN, J.; VALENZUELA, F.; BASUALTO, C.

2002-01-01

Kraft bleached cellulose from Pinus radiata was submitted to methylation reactions in heterogeneous media. After activation with 29% (w/w) NaOH solution, methylation reactions were carried out both with dimethyl sulfate (DMS) and methyl iodide (MI). The effects of the pressing ratio, reaction time and type of methylation agent were studied. The better yields were obtained with dimethylsulphate and the pressing ratio and reaction time were not signficant over the yield. Methylcellulose (MC) of...

Interactions between wall rocks around magma and hot water. Magma shuhen no hekigan/nessui sogo sayo

Energy Technology Data Exchange (ETDEWEB)

Fujimoto, K.

1992-12-01

This paper describes interactions between wall rocks around magma and hot water. The paper discusses effects of hydrothermal environments on dynamic properties of rock minerals with respect to hydrolytic weakening (decrease in dynamic strength of a mineral under presence of water) and reaction enhanced deformation (deformation accelerated by chemical change occurring in a mineral itself). It also explains chemical reactivity of minerals under hydrothermal enviroments with respect to four types of chemical changes in minerals, factors governing mineral dissolution rates, and importance of equilibrium and non-equilibrium in main components in reactions between minerals and waters. These statements quote mainly results of indoor experiments. The paper indicates the following matters as problems to be discussed on interactions between wall rocks around intrusive rocks and hot waters: Deviation from chemical equilibrium in reactions between rocks and waters; change in permeability as a result of reactions between rocks and waters; and possibilities of hydrolytic weakening in rocks around intrusive rock bodies. 52 refs., 6 figs.

Reaction of chlorine nitrate with hydrogen chloride and water at Antarctic stratospheric temperatures

Science.gov (United States)

Tolbert, Margaret A.; Rossi, Michel J.; Malhotra, Ripudaman; Golden, David M.

1987-01-01

Laboratory studies of heterogeneous reactions important for ozone depletion over Antarctica are reported. The reaction of chlorine nitrate (ClONO2) with H2O and HCl on surfacers that simulate polar stratospheric clouds are studied at temperatures relevant to the Antarctic stratosphere. The gaseous products of the resulting reactions, HOCl, Cl2O, and Cl2, could readily photolyze in the Antarctic spring to produce active chlorine for ozone depletion. Furthermore, the additional formation of condensed-phase HNO3 could serve as a sink for odd nitrogen species that would otherwise scavenge the active chlorine.

Supercritical carbon dioxide as an innovative reaction medium for selective oxidation

Energy Technology Data Exchange (ETDEWEB)

Loeker, F.; Leitner, W. [Max-Planck-Institut fuer Kohlenforschung, Muelheim an der Ruhr (Germany)

1998-12-31

Although the catalytic efficiency of all catalytic oxidation processes studied in scCO{sub 2} up to now is far from being satisfactory, the principle possibility to carry out such reactions in this medium is clearly evident. Future research in our group will be directed towards the development of homogeneous and heterogeneous catalysts that are adopted to the special requirements of both the oxidation process and the supercritical reaction medium. Preliminary results from these studies regarding the epoxidation of olefins with molecular oxygen as oxidant will be presented on the conference poster. (orig.)

An experimental study of the heterogeneous LMFBR core using FCA assemblies with axial internal blanket

International Nuclear Information System (INIS)

Nakano, M.; Iijima, S.; Shirakata, K.; Hirota, J.

1980-01-01

To investigate physics properties of the heterogeneous LMFBR core and to examine the reliability of the current data and method for heterogeneous core configuration, an experimental study has been made on FCA VII-3 assemblies which have an internal blanket (IB) at midplane of the cylindrical core. Systematic experiments were carried out on the heterogeneous cores whose IBs were different in composition and thickness. A homogeneous core was also built to compare the results with those obtained on the heterogeneous cores. The sodium-void worth is not sensitive to the composition of IB. The positive void worth in the core of the 40 cm IB is lowered by about 40% compared with that in the homogeneous core. The analysis was made using the JAERI-Fast Set Version II and the diffusion code CITATION. Directional diffusion coefficients were used to take account of the axial streaming. To evaluate transport effects, the S 4 calculation was made. Comparison between the calculated and experimental results reveals the following: ksub(eff) and Pu worth in the core are not well predicted for the heterogeneous core, although they are represented satisfactorily for the homogeneous core. Reaction rates sensitive to the low-energy neutron are underestimated in the IB when they are normalized in the core. Sodium-void worths are fairly well predicted. However, the positive void worth in the heterogeneous core is underestimated, while that in the homogeneous core is overestimated. (author)

Discontinuous Galerkin methods and a posteriori error analysis for heterogenous diffusion problems

International Nuclear Information System (INIS)

Stephansen, A.F.

2007-12-01

In this thesis we analyse a discontinuous Galerkin (DG) method and two computable a posteriori error estimators for the linear and stationary advection-diffusion-reaction equation with heterogeneous diffusion. The DG method considered, the SWIP method, is a variation of the Symmetric Interior Penalty Galerkin method. The difference is that the SWIP method uses weighted averages with weights that depend on the diffusion. The a priori analysis shows optimal convergence with respect to mesh-size and robustness with respect to heterogeneous diffusion, which is confirmed by numerical tests. Both a posteriori error estimators are of the residual type and control the energy (semi-)norm of the error. Local lower bounds are obtained showing that almost all indicators are independent of heterogeneities. The exception is for the non-conforming part of the error, which has been evaluated using the Oswald interpolator. The second error estimator is sharper in its estimate with respect to the first one, but it is slightly more costly. This estimator is based on the construction of an H(div)-conforming Raviart-Thomas-Nedelec flux using the conservativeness of DG methods. Numerical results show that both estimators can be used for mesh-adaptation. (author)

CuCo2O4 nanoplate film as a low-cost, highly active and durable catalyst towards the hydrolytic dehydrogenation of ammonia borane for hydrogen production

Science.gov (United States)

Liu, Quanbing; Zhang, Shengjie; Liao, Jinyun; Feng, Kejun; Zheng, Yuying; Pollet, Bruno G.; Li, Hao

2017-07-01

Catalytic dehydrogenation of ammonia borane is one of the most promising routes for the production of clean hydrogen as it is seen as a highly efficient and safe method. However, its large-scale industrial application is either limited by the high cost of the catalyst (usually a noble metal based catalyst) or by the low activity and poor reusability (usually a non-noble metal catalyst). In this study, we have successfully prepared three low-cost CuCo2O4 nanocatalysts, namely: (i) Ti supported CuCo2O4 film made of CuCo2O4 nanoplates, (ii) Ti supported CuCo2O4 film made of CuCo2O4 nanosheets, and (iii) unsupported CuCo2O4 nanoparticles. Among the three catalysts used for the hydrolytic dehydrogeneration of ammonia borane, the CuCo2O4 nanoplate film exhibits the highest catalytic activity with a turnover frequency (TOF) of ∼44.0 molhydrogen min-1 molcat-1. This is one of the largest TOF value for noble-metal-free catalysts ever reported in the literature. Moreover, the CuCo2O4 nanoplate film almost keeps its original catalytic activity after eight cycles, indicative of its high stability and good reusability. Owing to its advantages, the CuCo2O4 nanoplate film can be a promising catalyst for the hydrolytic dehydrogenation of ammonia borane, which may find important applications in the field of hydrogen energy.

The utilization of leftover as acid catalyst to catalyse the transesterification and esterification reactions

Science.gov (United States)

Leung, K. K.; Yau, Y. H.

2017-08-01

Biodiesel (Fatty Acid Methyl Ester, FAME) is a green and renewable energy. It is carbon neutral and produces less air pollutants in combustion. In my project, the selected feedstock of biodiesel production is grease trap oil (GTO). It is extracted from restaurants, and needs pre-treatment. The triglycerides and free fatty acid (FFA) are the main components of GTO. Both triglycerides and free fatty acid can be converted to biodiesel (Fatty Acid Methyl Ester) by transesterification and esterification, through reaction with alcohol (methanol) and catalyst. In the processes, acidic catalyst is chosen to speed up the reactions. The catalyst used In the study, a heterogeneous solid acid is applied. It is waste cooked rice (WCR) collected from leftover. The WCR powder is pyrolysed in 400°C furnace 15 hours and blown with nitrogen gas (incomplete carbonization). The WCR black powder is then mixed with concentrated sulphuric acid and heat in 160°C furnace 15 hours and continuous blown with nitrogen gas (sulphonation). This heterogeneous solid acid is used in the both transesterification and esterification to produce FAME. Moreover, in the optimal reaction conditions, this catalyst offers a stable catalytic effect. After 20 times usage in optimal reaction condition, the catalytic activity remains unchanged.

Propagation and diffusion-limited extinction of nonadiabatic heterogeneous flame in the SHS process

International Nuclear Information System (INIS)

Makino, Atsushi

1994-01-01

Nonadiabatic heterogeneous flame propagation and extinction in self-propagating high-temperature synthesis (SHS) are analyzed based on a premixed mode of propagation for the bulk flame supported by the nonpremixed reaction of dispersed nonmetals in the liquid metal. The formulation allows for volumetric heat loss throughout the bulk flame, finite-rate Arrhenius reaction at the particle surface, and temperature-sensitive Arrhenius mass diffusion in the liquid. Results show that, subsequent to melting of the metal, the flame structure consists of a relatively thin diffusion-consumption/convection zone followed by a relatively thick convection-loss zone, that the flame propagation rate decreases with increasing heat loss, that at a critical heat-loss rate the flame extinguishes as indicated by the characteristic turning-point behavior, that the surface reaction is diffusion limited such that the nonlinear, temperature-sensitive nature of the system is actually a consequence of the Arrhenius mass diffusion, and that extinction is sensitively affected by the mixture ratio, the degree of dilution, the initial temperature of the compact, and the size of the nonmetal particles. An explicit expression is derived for the normalized mass burning rate, which exhibits the characteristic turning point and shows that extinction occurs when this value is reduced to e -1/2 , which is the same as that for the nonadiabatic gaseous premixed flame. It is further shown that the theoretical results agree well with available experimental data, indicating that the present formulation captures the essential features of the nonadiabatic heterogeneous SHS processes and its potential for extension to describe other SHS phenomena

[How aliphatic alcohols and ph affect reactional capability of the horse blood serum cholinesterase at its interaction with organophosphorus inhibitors].

Science.gov (United States)

Basova, N E; Kormilitsin, B N; Perchenok, A Iu; Rozengart, E V; Saakov, V S; Suvorov, A A

2013-01-01

There was studied action of aliphatic alcohols (ethanol, propanol, isopropanol, n-butanol, isobutanol, secbutanol, tretbetanol) and pH on various kinds of reactional capability the serum cholinesterase. At the alcohols-affected inhibition of the cholinesterase hydrolytic activity, the determining role was played not the total number carbon atoms in the alcohol molecule, but by the "effective length" of the carbohydrate chain. The fact that the presence of alcohols did not affect parameters of the reverse cholinesterase inhibition with onium ions tetramethylammonium and choline allows suggesting the absence of effect solvents on specific acetylcholine sorption in the enzyme active center. With aid of two rows of hydrophobic organophosphorus inhibitors (OPI), we have managed to estimate both the degree and the character itself of the modifying action of alcohols and pH on the process of irreversible inhibition of serum cholinesterase.

The coupling effect of gas-phase chemistry and surface reactions on oxygen permeation and fuel conversion in ITM reactors

KAUST Repository

Hong, Jongsup

2015-08-01

© 2015 Elsevier B.V. The effect of the coupling between heterogeneous catalytic reactions supported by an ion transport membrane (ITM) and gas-phase chemistry on fuel conversion and oxygen permeation in ITM reactors is examined. In ITM reactors, thermochemical reactions take place in the gas-phase and on the membrane surface, both of which interact with oxygen permeation. However, this coupling between gas-phase and surface chemistry has not been examined in detail. In this study, a parametric analysis using numerical simulations is conducted to investigate this coupling and its impact on fuel conversion and oxygen permeation rates. A thermochemical model that incorporates heterogeneous chemistry on the membrane surface and detailed chemical kinetics in the gas-phase is used. Results show that fuel conversion and oxygen permeation are strongly influenced by the simultaneous action of both chemistries. It is shown that the coupling somewhat suppresses the gas-phase kinetics and reduces fuel conversion, both attributed to extensive thermal energy transfer towards the membrane which conducts it to the air side and radiates to the reactor walls. The reaction pathway and products, in the form of syngas and C2 hydrocarbons, are also affected. In addition, the operating regimes of ITM reactors in which heterogeneous- or/and homogeneous-phase reactions predominantly contribute to fuel conversion and oxygen permeation are elucidated.

Breast Cancer Redox Heterogeneity Detectable with Chemical Exchange Satruation Transfer (CEST) MRI

Science.gov (United States)

Cai, Kejia; Xu, He N.; Singh, Anup; Moon, Lily; Haris, Mohammad; Reddy, Ravinder; Li, Lin

2014-01-01

Purpose Tissue redox state is an important mediator of various biological processes in health and diseases such as cancer. Previously, we discovered that the mitochondrial redox state of ex vivo tissues detected by redox scanning (an optical imaging method) revealed interesting tumor redox state heterogeneity that could differentiate tumor aggressiveness. Because the noninvasive chemical exchange saturation transfer (CEST) MRI can probe the proton transfer and generate contrasts from endogenous metabolites, we aim to investigate if the in vivo CEST contrast is sensitive to proton transfer of the redox reactions so as to reveal the tissue redox states in breast cancer animal models. Procedures CEST MRI has been employed to characterize tumor metabolic heterogeneity and correlated with the redox states measured by the redox scanning in two human breast cancer mouse xenograft models, MDA-MB-231 and MCF-7. The possible biological mechanism on the correlation between the two imaging modalities was further investigated by phantom studies where the reductants and the oxidants of the representative redox reactions were measured. Results The CEST contrast is found linearly correlated with NADH concentration and the NADH redox ratio with high statistical significance, where NADH is the reduced form of nicotinamide adenine dinucleotide. The phantom studies showed that the reductants of the redox reactions have more CEST contrast than the corresponding oxidants, indicating that higher CEST effect corresponds to the more reduced redox state. Conclusions This preliminary study suggests that CEST MRI, once calibrated, might provide a novel noninvasive imaging surrogate for the tissue redox state and a possible diagnostic biomarker for breast cancer in the clinic. PMID:24811957

Discontinuous Galerkin methods and a posteriori error analysis for heterogenous diffusion problems; Methodes de Galerkine discontinues et analyse d'erreur a posteriori pour les problemes de diffusion heterogene

Energy Technology Data Exchange (ETDEWEB)

Stephansen, A.F

2007-12-15

In this thesis we analyse a discontinuous Galerkin (DG) method and two computable a posteriori error estimators for the linear and stationary advection-diffusion-reaction equation with heterogeneous diffusion. The DG method considered, the SWIP method, is a variation of the Symmetric Interior Penalty Galerkin method. The difference is that the SWIP method uses weighted averages with weights that depend on the diffusion. The a priori analysis shows optimal convergence with respect to mesh-size and robustness with respect to heterogeneous diffusion, which is confirmed by numerical tests. Both a posteriori error estimators are of the residual type and control the energy (semi-)norm of the error. Local lower bounds are obtained showing that almost all indicators are independent of heterogeneities. The exception is for the non-conforming part of the error, which has been evaluated using the Oswald interpolator. The second error estimator is sharper in its estimate with respect to the first one, but it is slightly more costly. This estimator is based on the construction of an H(div)-conforming Raviart-Thomas-Nedelec flux using the conservativeness of DG methods. Numerical results show that both estimators can be used for mesh-adaptation. (author)

Deciphering the Astrocyte Reaction in Alzheimer’s Disease

Directory of Open Access Journals (Sweden)

Beatriz G. Perez-Nievas

2018-04-01

Full Text Available Reactive astrocytes were identified as a component of senile amyloid plaques in the cortex of Alzheimer’s disease (AD patients several decades ago. However, their role in AD pathophysiology has remained elusive ever since, in part owing to the extrapolation of the literature from primary astrocyte cultures and acute brain injury models to a chronic neurodegenerative scenario. Recent accumulating evidence supports the idea that reactive astrocytes in AD acquire neurotoxic properties, likely due to both a gain of toxic function and a loss of their neurotrophic effects. However, the diversity and complexity of this glial cell is only beginning to be unveiled, anticipating that astrocyte reaction might be heterogeneous as well. Herein we review the evidence from mouse models of AD and human neuropathological studies and attempt to decipher the main conundrums that astrocytes pose to our understanding of AD development and progression. We discuss the morphological features that characterize astrocyte reaction in the AD brain, the consequences of astrocyte reaction for both astrocyte biology and AD pathological hallmarks, and the molecular pathways that have been implicated in this reaction.

An heterogeneous nucleation model for the irradiation coloring of alkali halides

International Nuclear Information System (INIS)

Aguilar, M.; Jaque, F.; Agullo-Lopez, F.

1980-01-01

An heterogeneous nucleation model for the radiation-induced coloring of alkali halides is presented. The model assumes a primary mechanism producing F and H pairs, followed by secondary thermally activated reactions including F-H recombination as well interstitial capture. The existence of a very unstable interstitial aggregate is explicitely considered. The model is able to account for the three-stages structure of the F-coloring curve and the inhibition in the occurrence of the late-stage by lowering dose-rate or by impurity doping

Pd enhanced WC catalyst to promote heterogeneous methane combustion

International Nuclear Information System (INIS)

Terracciano, Anthony Carmine; De Oliveira, Samuel; Siddhanti, Deepti; Blair, Richard; Vasu, Subith S.; Orlovskaya, Nina

2017-01-01

Highlights: • Pd enhanced WC catalyst particles were synthesized via mechanochemical alloying. • Catalyst was characterized by XRD, XRF, SEM, and EDS. • Catalyst was deposited on porous ZrO_2 and evaluated in heterogeneous combustion. • During combustion temperature profiles and spectral emissions were collected. - Abstract: The efficiency of combustion for low cost heat production could be greatly enhanced if an active and low cost catalyst would be used to facilitate the chemical reactions occurring during combustor operation. Within this work an experimental study of palladium (Pd) enhanced tungsten carbide (WC) catalyst, synthesized via high energy ball milling and deposited by dip coating onto a magnesia partially stabilized zirconia (MgO-ZrO_2) porous matrix of 10 ppin was evaluated in heterogeneous methane combustion. The synthesized powder was characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) analysis, as well as by X-ray Fluorescence (XRF); and the morphology of the deposited WC-Pd coating was also characterized using SEM and EDS. Performance evaluation of the heterogeneous combustor with WC-Pd coated MgO-ZrO_2 porous media was conducted at constant air flow rate and various equivalence ratios of methane/air gaseous mixtures, while monitoring axial temperature profiles within the combustion chamber using thermocouples, as well as thermal radiative and acoustic emissions from the combustor exhaust using an externally placed CCD camera and a microphone. It was found that there is a strong dependence of flame position and maximum temperature on equivalence ratio (φ) over the range of 0.47 ± 0.02 ⩽ φ ⩽ 0.75 ± 0.02. Additionally it was found that over the same equivalence ratio range, there is a characteristic 4 peak acoustic signature between 200 and 500 Hz. It was found that at higher equivalence ratios 0.51 ± 0.02 ⩽ φ ⩽ 0.75 ± 0.02 the performance of combustor

CFD analysis of a symmetrical planar SOFC with heterogeneous electrode properties

International Nuclear Information System (INIS)

Shi Junxiang; Xue Xingjian

2010-01-01

A comprehensive 2-D CFD model is developed to investigate bi-electrode supported cell (BSC) performance. The model takes into account the coupled complex transport phenomena of mass/heat transfer, charge (electron/ion) transport, and electrochemical reactions. The uniqueness of this modeling work is that heterogeneous electrode properties are taken into account, which includes not only linear functionally graded porosity distribution but also various nonlinear distributions in a general sense according to porous electrode features in BSC design. Extensive numerical analysis is performed to elucidate various heterogeneous porous electrode property effects on cell performance. Results indicate that cell performance is strongly dependent on porous microstructure distributions of electrodes. Among the various porosity distributions, inverse parabolic porosity distribution shows promising effects on cell performance. For a given porosity distribution of electrodes, cell performance is also dependent on operating conditions, typically fuel/gas pressure losses across the electrodes. The mathematical model developed in this paper can be utilized for high performance BSC SOFC design and optimization.

Microwave activation of palladium nanoparticles for enhanced ethanol electrocatalytic oxidation reaction in alkaline medium

CSIR Research Space (South Africa)

Rohwer, MB

2015-02-01

Full Text Available in alkaline medium (in terms of high mass activity stability and fast reaction kinetics). The remarkable microwave-induced properties on the Pd catalyst promise to revolutionize the use of microwave for catalyst activation for enhanced heterogeneous catalysis...

On the validity of effective formulations for transport through heterogeneous porous media

Science.gov (United States)

de Dreuzy, Jean-Raynald; Carrera, Jesus

2016-04-01

Geological heterogeneity enhances spreading of solutes and causes transport to be anomalous (i.e., non-Fickian), with much less mixing than suggested by dispersion. This implies that modeling transport requires adopting either stochastic approaches that model heterogeneity explicitly or effective transport formulations that acknowledge the effects of heterogeneity. A number of such formulations have been developed and tested as upscaled representations of enhanced spreading. However, their ability to represent mixing has not been formally tested, which is required for proper reproduction of chemical reactions and which motivates our work. We propose that, for an effective transport formulation to be considered a valid representation of transport through heterogeneous porous media (HPM), it should honor mean advection, mixing and spreading. It should also be flexible enough to be applicable to real problems. We test the capacity of the multi-rate mass transfer (MRMT) model to reproduce mixing observed in HPM, as represented by the classical multi-Gaussian log-permeability field with a Gaussian correlation pattern. Non-dispersive mixing comes from heterogeneity structures in the concentration fields that are not captured by macrodispersion. These fine structures limit mixing initially, but eventually enhance it. Numerical results show that, relative to HPM, MRMT models display a much stronger memory of initial conditions on mixing than on dispersion because of the sensitivity of the mixing state to the actual values of concentration. Because MRMT does not restitute the local concentration structures, it induces smaller non-dispersive mixing than HPM. However long-lived trapping in the immobile zones may sustain the deviation from dispersive mixing over much longer times. While spreading can be well captured by MRMT models, in general non-dispersive mixing cannot.

Isotopic constraints on heterogeneous sulfate production in Beijing haze

Directory of Open Access Journals (Sweden)

P. He

2018-04-01

Full Text Available Discerning mechanisms of sulfate formation during fine-particle pollution (referred to as haze hereafter in Beijing is important for understanding the rapid evolution of haze and for developing cost-effective air pollution mitigation strategies. Here we present observations of the oxygen-17 excess of PM2.5 sulfate (Δ17O(SO42− collected in Beijing haze from October 2014 to January 2015 to constrain possible sulfate formation pathways. Throughout the sampling campaign, the 12-hourly averaged PM2.5 concentrations ranged from 16 to 323 µg m−3 with a mean of (141  ±  88 (1σ µg m−3, with SO42− representing 8–25 % of PM2.5 mass. The observed Δ17O(SO42− varied from 0.1 to 1.6 ‰ with a mean of (0.9  ±  0.3 ‰. Δ17O(SO42− increased with PM2.5 levels in October 2014 while the opposite trend was observed from November 2014 to January 2015. Our estimate suggested that in-cloud reactions dominated sulfate production on polluted days (PDs, PM2.5  ≥  75 µg m−3 of Case II in October 2014 due to the relatively high cloud liquid water content, with a fractional contribution of up to 68 %. During PDs of Cases I and III–V, heterogeneous sulfate production (Phet was estimated to contribute 41–54 % to total sulfate formation with a mean of (48  ±  5 %. For the specific mechanisms of heterogeneous oxidation of SO2, chemical reaction kinetics calculations suggested S(IV ( =  SO2 ⚫ H2O + HSO3−  +  SO32− oxidation by H2O2 in aerosol water accounted for 5–13 % of Phet. The relative importance of heterogeneous sulfate production by other mechanisms was constrained by our observed Δ17O(SO42−. Heterogeneous sulfate production via S(IV oxidation by O3 was estimated to contribute 21–22 % of Phet on average. Heterogeneous sulfate production pathways that result in zero-Δ17O(SO42−, such as S(IV oxidation by NO2 in aerosol water and/or by O2 via a

elucidating the mechanism of the adsorption of mucin to ...

African Journals Online (AJOL)

dcu user

The major degradation reactions associated with alkyds during exposure to outdoor environment have been identified2 as photodegradation due to the attack of the UVB component of the solar radiation and hydrolytic degradation due to acid rain. The level of such degradative reactions would be expected to be greater iin ...

Morphological impact on the reaction kinetics of size-selected cobalt oxide nanoparticles

International Nuclear Information System (INIS)

Bartling, Stephan; Meiwes-Broer, Karl-Heinz; Barke, Ingo; Pohl, Marga-Martina

2015-01-01

Apart from large surface areas, low activation energies are essential for efficient reactions, particularly in heterogeneous catalysis. Here, we show that not only the size of nanoparticles but also their detailed morphology can crucially affect reaction kinetics, as demonstrated for mass-selected, soft-landed, and oxidized cobalt clusters in a 6 nm to 18 nm size range. The method of reflection high-energy electron diffraction is extended to the quantitative determination of particle activation energies which is applied for repeated oxidation and reduction cycles at the same particles. We find unexpectedly small activation barriers for the reduction reaction of the largest particles studied, despite generally increasing barriers for growing sizes. We attribute these observations to the interplay of reaction-specific material transport with a size-dependent inner particle morphology

Chitosan supported bimetallic Pd/Co nanoparticles as a heterogeneous catalyst for the reduction of nitroaromatics to amines

Directory of Open Access Journals (Sweden)

Sajjad Keshipour

2017-01-01

Full Text Available A new bimetallic nanocomposite of chitosan was prepared. Pd and Co nanoparticles were deposited on chitosan to produce a new heterogeneous recyclable catalyst for use in the bimetallic catalytic reduction reaction. The catalyst was characterized with common analysis methods for nanocomposites including Energy Dispersive X-Ray Spectroscopy, X-Ray Diffraction pattern, Thermal Gravimetric Analysis, Flame Atomic Absorption Spectroscopy and Scanning Electron Microscopy, and applied in the reduction reaction of nitroaromatics using NaBH4 at room temperature. The bimetallic system gave good results compared to each of the applied metals. Various aromatic amines and diamines were used in the reduction reaction. The aromatic amines were obtained as the sole product of the reduction reaction with 15 mol% Pd and 12 mol% Co during 2h. This reaction had some advantages such as mild reaction conditions, high yield, green solvent, and a recyclable catalyst. Also, the recovered catalyst was applicable in the reduction reaction without a significant decrease in the activity for up to six times.

Biomass production and secretion of hydrolytic enzymes are influenced by the structural complexity of the nitrogen source in Fusarium oxysporum and Aspergillus nidulans.

Science.gov (United States)

da Silva, M C; Bertolini, M C; Ernandes, J R

2001-01-01

The structural complexity of the nitrogen sources strongly affects biomass production and secretion of hydrolytic enzymes in filamentous fungi. Fusarium oxysporum and Aspergillus nidulans were grown in media containing glucose or starch, and supplemented with a nitrogen source varying from a single ammonium salt (ammonium sulfate) to free amino acids (casamino acids), peptides (peptone) and protein (gelatin). In glucose, when the initial pH was adjusted to 5.0, for both microorganisms, higher biomass production occurred upon supplementation with a nitrogen source in the peptide form (peptone and gelatin). With a close to neutrality pH, biomass accumulation was lower only in the presence of the ammonium salt. When grown in starch, biomass accumulation and secretion of hydrolytic enzymes (amylolytic and proteolytic) by Fusarium also depended on the nature of the nitrogen supplement and the pH. When the initial pH was adjusted to 5.0, higher growth and higher amylolytic activities were detected in the media supplemented with peptone, gelatin and casamino acids. However, at pH 7.0, higher biomass accumulation and higher amylolytic activities were observed upon supplementation with peptone or gelatin. Ammonium sulfate and casamino acids induced a lower production of biomass, and a different level of amylolytic enzyme secretion: high in ammonium sulfate and low in casamino acids. Secretion of proteolytic activity was always higher in the media supplemented with peptone and gelatin. Aspergillus, when grown in starch, was not as dependent as Fusarium on the nature of nitrogen source or the pH. The results described in this work indicate that the metabolism of fungi is regulated not only by pH, but also by the level of structural complexity of the nitrogen source in correlation to the carbon source.

Heterogeneous kinetics of the reduction of chromium (VI) by elemental iron

International Nuclear Information System (INIS)

Fiuza, Antonio; Silva, Aurora; Carvalho, Goreti; Fuente, Antonio V. de la; Delerue-Matos, Cristina

2010-01-01

Zero valent iron (ZVI) has been extensively used as a reactive medium for the reduction of Cr(VI) to Cr(III) in reactive permeable barriers. The kinetic rate depends strongly on the superficial oxidation of the iron particles used and the preliminary washing of ZVI increases the rate. The reaction has been primarily modelled using a pseudo-first-order kinetics which is inappropriate for a heterogeneous reaction. We assumed a shrinking particle type model where the kinetic rate is proportional to the available iron surface area, to the initial volume of solution and to the chromium concentration raised to a power α which is the order of the chemical reaction occurring at surface. We assumed α = 2/3 based on the likeness to the shrinking particle models with spherical symmetry. Kinetics studies were performed in order to evaluate the suitability of this approach. The influence of the following parameters was experimentally studied: initial available surface area, chromium concentration, temperature and pH. The assumed order for the reaction was confirmed. In addition, the rate constant was calculated from data obtained in different operating conditions. Digital pictures of iron balls were periodically taken and the image treatment allowed for establishing the time evolution of their size distribution.

Genetic heterogeneity of retinitis pigmentosa

OpenAIRE

Hartono, Hartono

2015-01-01

Genetic heterogeneity is a phenomenon in which a genetic disease can be transmitted by several modes of inheritance. The understanding of genetic heterogeneity is important in giving genetic counselling.The presence of genetic heterogeneity can be explained by the existence of:1.different mutant alleles at a single locus, and2.mutant alleles at different loci affecting the same enzyme or protein, or affecting different enzymes or proteins.To have an overall understanding of genetic heterogene...

Well-defined silica-supported zirconium–imido complexes mediated heterogeneous imine metathesis

KAUST Repository

Hamzaoui, Bilel

2016-02-15

Upon prolonged thermal exposure under vacuum, a well-defined single-site surface species [(≡Si-O-)Zr(NEt2)3] (1) evolves into an ethylimido complex [(≡Si-O-)Zr(=NEt)NEt2] (2). Reactions of 2 with an imine substrate result in imido/imine (=NRi, R: Et, Ph) exchange (metathesis) with the formation of [(≡Si-O-)Zr(=NPh)NEt2] (3). Compounds 2 and 3 effectively catalyze imine/imine cross-metathesis and are thus considered as the first heterogeneous catalysts active for imine metathesis. © The Royal Society of Chemistry 2016.

Well-defined silica-supported zirconium–imido complexes mediated heterogeneous imine metathesis

KAUST Repository

Hamzaoui, Bilel; Pelletier, Jeremie; Abou-Hamad, Edy; Basset, Jean-Marie

2016-01-01

Upon prolonged thermal exposure under vacuum, a well-defined single-site surface species [(≡Si-O-)Zr(NEt2)3] (1) evolves into an ethylimido complex [(≡Si-O-)Zr(=NEt)NEt2] (2). Reactions of 2 with an imine substrate result in imido/imine (=NRi, R: Et, Ph) exchange (metathesis) with the formation of [(≡Si-O-)Zr(=NPh)NEt2] (3). Compounds 2 and 3 effectively catalyze imine/imine cross-metathesis and are thus considered as the first heterogeneous catalysts active for imine metathesis. © The Royal Society of Chemistry 2016.

Bifunctional nanocrystalline MgO for chiral epoxy ketones via Claisen-Schmidt condensation-asymmetric epoxidation reactions.

Science.gov (United States)

Choudary, Boyapati M; Kantam, Mannepalli L; Ranganath, Kalluri V S; Mahendar, Koosam; Sreedhar, Bojja

2004-03-24

Design and development of a truly nanobifunctional heterogeneous catalyst for the Claisen-Schmidt condensation (CSC) of benzaldehydes with acetophenones to yield chalcones quantitatively followed by asymmetric epoxidation (AE) to afford chiral epoxy ketones with moderate to good yields and impressive ee's is described. The nanomagnesium oxide (aerogel prepared) NAP-MgO was found to be superior over the NA-MgO and CM-MgO in terms of activity and enantioselectivity as applicable in these reactions. An elegant strategy for heterogenization of homogeneous catalysts is presented here to evolve single-site chiral catalysts for AE by a successful transfer of molecular chemistry to surface metal-organic chemistry with the retention of activity, selectivity/enantioselectivity. Brønsted hydroxyls are established as sole contributors for the epoxidation reaction, while they add on to the CSC, which is largely driven by Lewis basic O2-sites. Strong hydrogen-bond interactions between the surface -OH on MgO and -OH groups of diethyl tartrate are found inducing enantioselectivity in the AE reaction. Thus, the nanocrystalline NAP-MgO with its defined shape, size, and accessible OH groups allows the chemisorption of TBHP, DET, and olefin on its surface to accomplish single-site chiral catalysts to provide optimum ee's in AE reactions.

Mathematical modeling in mechanics of heterogeneous media

International Nuclear Information System (INIS)

Fedorov, A.V.; Fomin, V.M.

1991-01-01

The paper reviews the work carried out at the Department of Multi-Phase Media Mechanics of the Institute of Theoretical and Applied Mechanics of the Siberian Division of the USSR Academy of Sciences. It deals with mathematical models for the flow of gas mixtures and solid particles that account for phase transitions and chemical reactions. This work is concerned with the problems of construction of laws of conservation, determination of the type of equations of heterogeneous media mechanics, structure of shock waves, and combined discontinuities in mixtures. The theory of ideal and nonideal detonation in suspension of matter in gases is discussed. Self-similar flows of gas mixtures and responding particles, as well as the problem of breakup of discontinuity for suspension of matter in gases, is studied. 42 refs

Effects of physical and geochemical heterogeneities on mineral transformation and biomass accumulation during biostimulation experiments at Rifle, Colorado.

Science.gov (United States)

Li, Li; Steefel, Carl I; Kowalsky, Michael B; Englert, Andreas; Hubbard, Susan S

2010-03-01

Electron donor amendment for bioremediation often results in precipitation of secondary minerals and the growth of biomass, both of which can potentially change flow paths and the efficacy of bioremediation. Quantitative estimation of precipitate and biomass distribution has remained challenging, partly due to the intrinsic heterogeneities of natural porous media and the scarcity of field data. In this work, we examine the effects of physical and geochemical heterogeneities on the spatial distributions of mineral precipitates and biomass accumulated during a biostimulation field experiment near Rifle, Colorado. Field bromide breakthrough data were used to infer a heterogeneous distribution of hydraulic conductivity through inverse transport modeling, while the solid phase Fe(III) content was determined by assuming a negative correlation with hydraulic conductivity. Validated by field aqueous geochemical data, reactive transport modeling was used to explicitly keep track of the growth of the biomass and to estimate the spatial distribution of precipitates and biomass. The results show that the maximum mineral precipitation and biomass accumulation occurs in the vicinity of the injection wells, occupying up to 5.4vol.% of the pore space, and is dominated by reaction products of sulfate reduction. Accumulation near the injection wells is not strongly affected by heterogeneities present in the system due to the ubiquitous presence of sulfate in the groundwater. However, accumulation in the down-gradient regions is dominated by the iron-reducing reaction products, whose spatial patterns are strongly controlled by both physical and geochemical heterogeneities. Heterogeneities can lead to localized large accumulation of mineral precipitates and biomass, increasing the possibility of pore clogging. Although ignoring the heterogeneities of the system can lead to adequate prediction of the average behavior of sulfate-reducing related products, it can also lead to an

Kinetic measurements of the hydrolytic degradation of cefixime: effect of Captisol complexation and water-soluble polymers.

Science.gov (United States)

Mallick, Subrata; Mondal, Arijit; Sannigrahi, Santanu

2008-07-01

We have taken kinetic measurements of the hydrolytic degradation of cefixime, and have studied the effect of Captisol complexation and water-soluble polymers on that degradation. The phase solubility of cefixime in Captisol was determined. Kinetic measurements were carried out as a function of pH and temperature. High-performance liquid chromatography (HPLC) was performed to assay all the samples of phase-solubility analysis and kinetic measurements. Chromatographic separation of the degradation products was also performed by HPLC. FT-IR spectroscopy was used to investigate the presence of any interaction between cefixime and Captisol and soluble polymer. The phase-solubility study showed A(L)-type behaviour. The pH-rate profile of cefixime exhibited a U-shaped profile whilst the degradation of cefixime alone was markedly accelerated with elevated temperature. A strong stabilizing influence of the cefixime-Captisol complexation and hypromellose was observed against aqueous mediated degradation, as compared with povidone and macrogol. The unfavourable effect of povidone and macrogol may have been due to the steric hindrance, which prevented the guest molecule from entering the cyclodextrin cavity, whereas hypromellose did not produce any steric hindrance.

Kinetics of liquid-phase catalytic heterogeneous protium-tritium isotope exchange with participation of gaseous hydrogen

International Nuclear Information System (INIS)

Akulov, G.P.; Snetkova, E.V.; Kayumov, V.G.; Kaminskij, Yu.L.

1990-01-01

Reaction rate constants of catalytic (PdO/BaSO 4 (Al 2 O 3 ) catalyst) heterogeneous protium - tritium isotopic exchange D - [1- 3 H] of carbohydrates and gaseous oxygen have been measured. It is ascertained that the rate of isotopic exchange depends on the nature of carbohydrate, catalyst, buffer and medium acidity. The value of concentration of carbohydrate acyclic forms plays the determining role in the process

Free energy diagram for the heterogeneous enzymatic hydrolysis of glycosidic bonds in cellulose

DEFF Research Database (Denmark)

Westh, Peter; Cruys-Bagger, Nicolaj; Sørensen, Trine Holst

2015-01-01

for all stable and activated complexes defined by the reaction scheme, and hence propose a free energy diagram for the full heterogeneous process. For other Cel7A enzymes, including variants with and without carbohydrate binding module (CBM), we obtained activation parameters for the association...... no influence on the transition state for association, but increased the free energy barrier for dissociation. Hence, the CBM appeared to promote the stability of the complex by delaying dissociation rather than accelerating association....

Heterogeneous reactors

International Nuclear Information System (INIS)

Moura Neto, C. de; Nair, R.P.K.

1979-08-01

The microscopic study of a cell is meant for the determination of the infinite multiplication factor of the cell, which is given by the four factor formula: K(infinite) = n(epsilon)pf. The analysis of an homogeneous reactor is similar to that of an heterogeneous reactor, but each factor of the four factor formula can not be calculated by the formulas developed in the case of an homogeneous reactor. A great number of methods was developed for the calculation of heterogeneous reactors and some of them are discussed. (Author) [pt

Heterogeneous gas core reactor

International Nuclear Information System (INIS)

Han, K.I.

1977-01-01

Preliminary investigations of a heterogeneous gas core reactor (HGCR) concept suggest that this potential power reactor offers distinct advantages over other existing or conceptual reactor power plants. One of the most favorable features of the HGCR is the flexibility of the power producing system which allows it to be efficiently designed to conform to a desired optimum condition without major conceptual changes. The arrangement of bundles of moderator/coolant channels in a fissionable gas or mixture of gases makes a truly heterogeneous nuclear reactor core. It is this full heterogeneity for a gas-fueled reactor core which accounts for the novelty of the heterogeneous gas core reactor concept and leads to noted significant advantages over previous gas core systems with respect to neutron and fuel economy, power density, and heat transfer characteristics. The purpose of this work is to provide an insight into the design, operating characteristics, and safety of a heterogeneous gas core reactor system. The studies consist mainly of neutronic, energetic and kinetic analyses of the power producing and conversion systems as a preliminary assessment of the heterogeneous gas core reactor concept and basic design. The results of the conducted research indicate a high potential for the heterogeneous gas core reactor system as an electrical power generating unit (either large or small), with an overall efficiency as high as 40 to 45%. The HGCR system is found to be stable and safe, under the conditions imposed upon the analyses conducted in this work, due to the inherent safety of ann expanding gaseous fuel and the intrinsic feedback effects of the gas and water coolant

Chemical stability of insulin. 1. Hydrolytic degradation during storage of pharmaceutical preparations.