Electron Donation–Backdonation and the Rules of Catalytic Promotion

Abstract

The rules of classical and electrochemical promotion of catalysis, which allow for the prediction of the effect of electropositive and electronegative promoters on catalytic rate and selectivity on the basis of the catalytic reaction kinetics, are compared with experiment for all relevant catalytic studies during the last two decades and are used to show that the rate versus catalyst work function dependence always parallels the rate versus electron donor reactant dependence. This generalized rule is rationalized both by considering the interaction of the electric field in the effective double layer at the metal catalyst–gas interface with the electric dipoles of the adsorbed reactants and also by considering the electron donation–backdonation between the adsorbed reactants and the catalyst. This generalized promotional rule allows for promoter selection on the basis of the reaction kinetics.