ASPECTS OF DISSOCIATIVE CHEMISORPTION AND PROMOTION IN CATALYSIS

Catalysis is a cyclic event in which reactants adsorb on the catalyst, react on the surface and desorb into the gas phase, leaving empty ads orption sites behind for the next catalytic cycle. Very often, at leas t one of the participating reactants has to dissociate. This paper qua litatively reviews the electronic interactions between an adsorbed mol ecule and the surface that lead to dissociation, and discusses in more detail how alkali metal promoters enhance this interaction by lowerin g the electrostatic surface potential. As a dissociating molecule gene rally needs an ensemble of several metal atoms, the kinetics of the di ssociation reaction depends sensitively on the surface coverage, as is illustrated for the dissociation of NO on rhodium.