Information on Intermediates Is the Basis for Understanding the Mechanism of Catalytic Action

Abstract

To determine the mechanism of a heterogeneous catalytic reaction, a spectrokinetic method was used based on the comparison of simultaneously measured rates of transformation of surface complexes using in situ IR spectroscopy and the rate of formation of reaction products. Based on the of systemic studies of intermediates of heterogeneous catalytic reactions by this method, general patterns are found that shed light on the essence of the catalytic action. It is found that the main function of the catalyst is the preparation of a new reagent from the molecule in the gas phase (during adsorption). The transformation of this regent into the products on the surface occurs via a route that is fundamentally different from the route of transformation of the initial molecule in a gas-phase reaction. It was also found that, if the initial adsorption forms of the reactants in the reaction under study are the same for a certain group of catalysts, then the mechanism (as a sequence of steps) of this reaction on these catalysts is the same. The individual properties of different catalysts within such a group are manifested in the difference in the ratio of the rates of steps, i.e. in determining the limiting step.