MECHANISM OF ADSORPTION, ELECTROREDUCTION AND HYDROGENATION OF COMPOUNDS WITH ETHYLENIC BONDS ON PLATINUM AND RHODIUM .1. KINETICS OF ADSORPTION AND ELECTROREDUCTION

The influence of various factors (concentration, potential, solution pH, surface coverage with the organic substance, temperature, etc.) on the adsorption and electroreduction of maleic acid and other ethylene compounds on platinum and rhodium has been investigated. Quantitative comparison of the results of adsorption and kinetic measurements carried out under similar conditions has made it possible to elucidate the mechanism of electroreduction. It is shown that the rate-determining step of the electroreduction process of maleic acid is the interaction of the chemisorbed particle of maleic acid with the adsorbed hydrogen which is formed at the preceding rapid stage of hydrogen ion discharge. Considerable differences in the rates of electroreduction of various ethylene compounds at a constant volume concentration result from a strong influence of substituents on the rate and value of the adsorption of a given ethylene compound. The presence of substitutents has only a very weak influence on the electroreduction rate constant as such. © 1979 Elsevier Sequoia S.A., Lausanne.