The Elovich differential equation. Hydrogen and oxygen adsorption on supported iridium

Abstract

The use of the selective chemisorption of hydrogen or oxygen for the determination of metal surface areas in catalysts consisting of iridium supported on silica or γ-alumina is subject to various difficulties. On the one hand, the hydrogen stoichiometry is found to vary with the nature of the support and the metal content, and in any case is larger than unity; on the other hand, oxygen adsorption coexists with a surface oxidation process which prevents the calculation of the oxygen uptake corresponding to monolayer coverage. The conventional application of the Elovich equation in its integrated form to kinetic data for adsorption cannot differentiate between the two existing processes. A method is proposed for the application of this equation in its differential form so that the two processes can be separated and a reliable value for the oxygen monolayer on the metal can be obtained.