KINETICS OF ELECTROCHEMICAL REACTIONS ON MODEL SUPPORTED CATALYSTS: READSORPTION AND MASS TRANSPORT

2008 ◽  
Vol 15 (06) ◽  
pp. 745-751
Author(s):  
VLADIMIR P. ZHDANOV ◽  
BENGT KASEMO
Keyword(s):  
Mass Transport ◽  
Supported Catalysts ◽  
Reaction Scheme ◽  
Electrochemical Reactions ◽  
Subsequent Reaction ◽  
Flow Cells ◽  
2D And 3D ◽  
Kinetics Of ◽  
And Diffusion

To bridge the structure gap, electrochemical reactions can be studied in flow cells with nm-sized catalyst particles deposited or fabricated on the cell walls. The understanding of the role of mass transport in such cells is now limited. To clarify the likely effects in this field, we analyze the simplest reaction scheme including intermediate desorption, readsorption, and subsequent reaction and show how the net rate of the formation of intermediate can be influenced by its diffusion in the liquid phase. With certain approximations, we derive analytical results describing reaction and diffusion near catalyst particles and in more remote regions in the simplest 1D case and more complex 2D and 3D situations.

scholarly journals A NEW METHOD TO DISTINGUISH SEPARATE COMPONENTS IN CYTOCHEMICALLY STAINED MACROMOLECULES BY ANALYSIS OF THE KINETICS OF THE STAINING AND DESTAINING PROCESSES

1973 ◽  
Vol 21 (8) ◽  
pp. 723-728 ◽  
Author(s):  
W. A. L. DUIJNDAM ◽  
J. HERMANS ◽  
P. VAN DUIJN
Keyword(s):  
Time Course ◽  
Diffusion Processes ◽  
Reaction Scheme ◽  
New Method ◽  
Pseudo First Order Reaction ◽  
The Individual ◽  
Macromolecular Substance ◽  
Kinetics Of ◽  
And Diffusion ◽  
Reaction Schemes

A new method making it possible to analyze properties of the end products of cytochemical staining reactions in macromolecular substances not expressed in the absorption spectra is described. Mathematical analysis of the course of changes in the absorbance during staining or destaining of the macromolecular substance provides information about the reaction velocities of these processes for the individual components present as well as about the concentrations of the components thus detected. This analysis is performed by a procedure of computerized curve-fitting between experimentally determined and theoretically expected absorbance curves. The theoretical time course of absorbance is derived for a number of pseudo first-order reaction schemes, and a description is given of the way in which the most appropriate reaction scheme can be recognized and the parameters are estimated, both on the basis of the experimental absorbance curve. Possible complications due to dye impurities, depolymerization and diffusion processes are discussed.

scholarly journals The role of mass transport in protein crystallization

2016 ◽  
Vol 72 (2) ◽  
pp. 96-104 ◽  
Author(s):  
Juan Manuel García-Ruiz ◽  
Fermín Otálora ◽  
Alfonso García-Caballero
Keyword(s):  
Mass Transport ◽  
Protein Crystallization ◽  
Protein Crystal ◽  
Diffusion Technique ◽  
Crystallization Experiment ◽  
Crystallization Experiments ◽  
Scale Range ◽  
Complex Phenomena ◽  
And Diffusion

Mass transport takes place within the mesoscopic to macroscopic scale range and plays a key role in crystal growth that may affect the result of the crystallization experiment. The influence of mass transport is different depending on the crystallization technique employed, essentially because each technique reaches supersaturation in its own unique way. In the case of batch experiments, there are some complex phenomena that take place at the interface between solutions upon mixing. These transport instabilities may drastically affect the reproducibility of crystallization experiments, and different outcomes may be obtained depending on whether or not the drop is homogenized. In diffusion experiments with aqueous solutions, evaporation leads to fascinating transport phenomena. When a drop starts to evaporate, there is an increase in concentration near the interface between the drop and the air until a nucleation event eventually takes place. Upon growth, the weight of the floating crystal overcomes the surface tension and the crystal falls to the bottom of the drop. The very growth of the crystal then triggers convective flow and inhomogeneities in supersaturation values in the drop owing to buoyancy of the lighter concentration-depleted solution surrounding the crystal. Finally, the counter-diffusion technique works if, and only if, diffusive mass transport is assured. The technique relies on the propagation of a supersaturation wave that moves across the elongated protein chamber and is the result of the coupling of reaction (crystallization) and diffusion. The goal of this review is to convince protein crystal growers that in spite of the small volume of the typical protein crystallization setup, transport plays a key role in the crystal quality, size and phase in both screening and optimization experiments.

Metamorphic reaction rate laws and development of isograds

1986 ◽  
Vol 50 (357) ◽  
pp. 359-373 ◽  
Author(s):  
Antonio C. Lasaga
Keyword(s):  
Diffusion Processes ◽  
Relative Role ◽  
Mineral Surfaces ◽  
Surface Kinetics ◽  
Rate Laws ◽  
Careful Treatment ◽  
Reaction Zones ◽  
Kinetics Of ◽  
And Diffusion

AbstractNew data on the kinetics of dehydration of muscovite + quartz suggest the necessity for a careful treatment of both surface kinetics and diffusion processes in metamorphic reactions. A new model is proposed that illustrates the relative role of diffusion and surface reactions in the overall metamorphic process. The rate law for the reaction at mineral surfaces derived from the experimental data is shown to be probably non-linear and similar to rate laws derived from Monte Carlo calculations. The experimental rate data is then used in a heat flow calculation to model the evolution of the muscovite isograd in the field. The position of the isograd, the temperature oversteps above equilibrium, and the width of ‘reaction zones’ are then analysed as a function of intrusion size and kinetic parameters.

Effects of ball-milling conditions and additives on the hydrogen sorption properties of Mg + 5 wt% Cr2O3 mixtures

2006 ◽  
Vol 21 (7) ◽  
pp. 1747-1752 ◽  
Author(s):  
J-L. Bobet ◽  
M. Kandavel ◽  
S. Ramaprabhu
Keyword(s):  
Particle Size ◽  
Sorption Process ◽  
Rate Equations ◽  
Desorption Kinetics ◽  
Yield Information ◽  
Order Of Magnitude ◽  
Effect Of Particle Size ◽  
Kinetics Of ◽  
And Diffusion

Effects of particle size of Cr2O3 catalyst on the hydrogen absorption/desorption kinetics of Mg + 5 wt% Cr2O3 mixtures have been studied. To explain the effect of particle size of Cr2O3 and also to yield information about the role of Cr2O3 during the sorption process, the kinetics data have been analyzed using Avrami–Erofeev rate equations. The activation energies and diffusion coefficients of these mixtures are in the ranges of 50.6–63.2 kJ/mol and 1.2.10−11 to 8.9.10−10 cm2/s, respectively. The addition of nano-oxides led to an increase of the diffusion coefficient of hydrogen by one order of magnitude.

Effect of cluster-gradient architecture of nanostructured topocomposites on features of tribointeraction with heterophased material

2020 ◽  
pp. 130-135
Author(s):  
D.N. Korotaev ◽  
K.N. Poleshchenko ◽  
E.N. Eremin ◽  
E.E. Tarasov
Keyword(s):  
Wear Resistance ◽  
Titanium Alloy ◽  
Energy Dissipation ◽  
Phase Structure ◽  
Diffusion Processes ◽  
Structural Phase ◽  
High Wear Resistance ◽  
Wear Characteristics ◽  
And Diffusion

The wear resistance and wear characteristics of cluster-gradient architecture (CGA) nanostructured topocomposites are studied. The specifics of tribocontact interaction under microcutting conditions is considered. The reasons for retention of high wear resistance of this class of nanostructured topocomposites are studied. The mechanisms of energy dissipation from the tribocontact zone, due to the nanogeometry and the structural-phase structure of CGA topocomposites are analyzed. The role of triboactivated deformation and diffusion processes in providing increased wear resistance of carbide-based topocomposites is shown. They are tested under the conditions of blade processing of heat-resistant titanium alloy.

The mechanism of the anionic coordination polymerization of isoprene

1980 ◽  
Vol 45 (9) ◽  
pp. 2391-2399 ◽  
Author(s):  
Miroslav Kašpar ◽  
Jiří Trekoval
Keyword(s):  
Chromatographic Method ◽  
Initial Period ◽  
Reaction Scheme ◽  
Polymerization Kinetics ◽  
Coordination Polymerization ◽  
Initial Concentration ◽  
The Cross ◽  
Gas Chromatographic Method ◽  
Kinetics Of

The polymerization kinetics of isoprene (2-methyl-1,3-butadiene) in benzene with butyllithium as the initiator was investigated by the gas chromatographic method. After completion of the initial period of the reaction, its order with respect to the initial concentration of initiator is negative at the concentrations of the latter between 0.01 and 0.25 mol/l, and positive at higher concentrations. A reaction scheme has been suggested with respect to the "cross" association of butyllithium and of the "living" oligoisoprene.

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