The effects of metal-oxygen bond strength on properties of oxides: II. Water-gas shift over bulk oxides

Abstract

The water-gas shift reaction was studied at temperatures near 650 K over a series of bulk oxide samples (Fe3O4, ZnFe2O4, MgFe2O4, ZnO, MgO, SnO2, Al2O3, TiO2, Na-mordenite, SiO2). Magnetite (Fe3O4) catalyzed the reaction via an oxidation/reduction, regenerative mechanism; and, the remaining oxides catalyzed the reaction through an associative mechanism involving an adsorbed intermediate believed to be a formate species. The catalytic activities of the oxides for which the associative mechanism was dominant increased as the metal-oxygen bond strength of the oxide decreased. Accordingly, basic oxides were more reactive than acidic oxides. This change in activity is interpreted in terms of the reactivity of oxygen or hydroxyl groups on the oxide surfaces. © 1986.