Computer simulations of photochemical water cleavage systems. 1. A kinetic model for the production of hydrogen on a colloidal catalyst
A mechanism is proposed for the colloidal-catalyst-mediated reduction of water to hydrogen by a reduced electron acceptor. Adsorption of several of the reactants is invoked, and electrons, hydrogen atoms, hydride ions, and molecular hydrogen, all adsorbed on the colloids, are suggested as probable intermediates. Adsorption of H/sup +/ and OH/sup -/ ions onto the catalyst surface at appropriate pH's is also postulated and electrostatic factors are introduced to account for the total electrical charge carried by the colloid. Computer simulations were performed for the change in concentration with time of the reduced methylviologen cation radical, MV/sup +/, in the presence of a colloidal platinum catalyst over the pH range 1-11, the range investigated in earlier pulse radiolysis studies. Values of the rate constants for the individual steps in the reduction process, obtained by optimizing the fits of the computer-simulated decays and growths with those obtained experimentally, are given. The changes occurring with time in the chemical system in the pH range 1-11 are described in detail. The effects on the computer-simulated plots of varying several of the parameters of the system such as the initial concentration of MV/sup +/, the concentration of methylviologen, MV/sup 2 +/, and the concentration of platinum are also described and in most cases good agreement is obtained with experiment. In particular, deviations from a first-order dependence of the rate of decay of MV/sup +/ on colloid concentration were found in their computer simulations similar to those found experimentally, and are attributed to changes in the coverage of the colloidal particles by adsorbed species as the concentration of catalyst is varied. Possible future refinements to their proposed model are also discussed briefly.
- Research Organization:
- Univ. of Notre Dame, IN
- OSTI ID:
- 5261418
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 90:19
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
HYDROGEN
CHEMICAL PREPARATION
WATER
PHOTOELECTROLYSIS
CATALYSTS
COLLOIDS
MATHEMATICAL MODELS
REDOX REACTIONS
THEORETICAL DATA
CHEMICAL REACTIONS
DATA
DISPERSIONS
ELECTROLYSIS
ELEMENTS
HYDROGEN COMPOUNDS
INFORMATION
LYSIS
NONMETALS
NUMERICAL DATA
OXYGEN COMPOUNDS
SYNTHESIS
080106* - Hydrogen- Production- Biosynthesis & Photochemical Processes
400500 - Photochemistry