The surface state representation of catalytic reactants and promoters

Abstract

To analyze charge transfer reactions on a semiconductor, the reactions are separated into steps involving chemical transformations and steps involving electron transfer (redox steps). With such a separation, the band model representation can be utilized in the description of the redox steps, with the reactants described in terms of their electronic energy levels or surface states. The identification of the appropriate surface states is discussed, and it is pointed out that for most redox couples two or more surface states must be considered in the analysis. A few illustrative examples are analyzed to show how one can utilize band theory concepts in the analysis of catalytic reactions. It is shown that the situation becomes much simpler to analyze if intentionally added redox couples are used as promoters. Moreover, in many cases where the electronic factor is important, such surface state promoters, if properly chosen, should enhance catalytic activity by orders of magnitude.