Supported oxide overlayers: A link between macroscopic and microscopic properties

Abstract

In this paper we examine supported oxide overlayer catalysts. We first show that, despite the possible combinations of support and overlayer employed, the whole class shows several chemical and structural analogies and can be treated as a uniform group. Based on the trends highlighted, we propose two different geometries of the interface, that we have labelled mechanical mixing and chemical deposition models. We further derive a set of equations that link the relevant experimental variables (overlayer loading, support face exposed, overlayer face exposed, oxidation state and local coordination number of the overlayer cation) with one another and to energy parameters obtained at the microscopic level. We show that the support modifies the reducibility of the overlayer cation and can even force a different stoichiometry in the overlayer, as suggested by the stability of our chemical deposition model at low loadings, thus influencing the catalytic behaviour of the supported phase.