Kinetic and mechanistic studies on direct H2O2 synthesis from H2 and O2 catalyzed by Pd in the presence of H+ and Br− in water: A comprehensive paper

Abstract

The kinetic analysis of direct H2O2 synthesis from H2 and O2 in water over Pd catalysts was summarized on the basis of our recent studies, which included mass-transfer processes as well as concurrent and consecutive side reactions. The parameters examined for the synthesis were the dependencies on H2 and O2 partial pressures, the effects of H+ and Br− ions, the influence of the Pd particle size, and the effects of catalyst supports. The reaction mechanisms were discussed based on the above results, the kinetics of the H2O2 decomposition, the Br− adsorption on the Pd catalysts, and the DFT calculation using the cluster models. Structure-sensitive catalysis was indicated here: there were coordinatively more unsaturated sites (Site A) and less unsaturated ones (Site B), and H2O2 would be produced selectively on Site B, whereas the direct H2O formation and the destruction of H2O2 would take place more easily on Site A. The latter decreased with adsorption of H+ and Br− in pairs. The effect of supports was discussed from the viewpoint of their isoelectric points. The direct H2O2 synthesis under practical conditions was simulated using the above results, and several parameters were suggested to be improved.