Surface characterization and catalytic activity of CoxMg1 –xAl2O4 solid solutions. Oxidation of carbon monoxide by oxygen

Abstract

Spinel solid solutions of Co_xMg_{1 –x}Al₂O₄ with x= 0–1 have been studied as catalysts for CO oxidation by molecular O₂. The experiments were performed either with or without CO₂ condensation. The apparent activation energies varied depending on the cobalt content and the procedure adopted. The activity per ion (turnover frequency) was fairly constant over the whole range of cobalt contents, when surface cobalt ion concentrations, as measured by X-ray photoelectron spectroscopy (XPS), are considered. It is inferred that each Co²⁺ ion is active irrespective of its concentration and configuration (isolated, in dimers or in clusters) and that the coordination (tetrahedral or octahedral) plays a minor role in the activity per ion. The reaction appears to be structure insensitive as opposed to the N₂O decomposition which appears to be concentration dependent. A mechanism of CO oxidation is proposed in terms of the nature and reactivity of the surface species formed on adsorption of O₂ and/or CO. The effect of CO₂ on the reaction rate is also discussed.