Linear Free Energy Relationships in Heterogeneous Catalysis. XII. Interpretation of the Catalytic Activity of Decomposition of Hydrogen Peroxide over Nickel Oxide on the Basis of Oxidation Power Distribution

Abstract

Abstract Kinetic studies have been carried out on the heterogeneous decomposition of hydrogen peroxide over several nickel oxide catalysts calcined at different temperatures. Kinetic parameters such as reaction order and apparent activation energy depend somewhat on the reaction conditions, but show practically no change with catalyst. The catalytic activity changes with calcination temperature, becoming minimum at 550 °C and maximum at 600 °C. The trend does not change with pretreatment of the catalyst, resembling the behavior of surface excess oxygen having a relatively higher oxidation power. Thus the distribution of oxidation power is closely related to catalytic activity for the decomposition of hydrogen peroxide. We therefore applied the regional analysis assuming that the surface excess oxygen represents active sites for catalysis, and a specific regional activity corresponds to each regional oxygen. It was found that the fifth region (the range of free energy change of adsorption of oxygen being from −11.1 to −12.6 kcal/mol) markedly contributes to the reaction rate, and the calculated rates agree with the observed ones. The nature of the active site was discussed as regards pretreatment of the catalyst.