The direct synthesis of hydrogen peroxide over Au and Pd nanoparticles: A DFT study

Catalysts consisting of Au, Pd and their alloys have been shown to be active oxidation catalysts. These materials can use dioxygen or hydrogen peroxide as the oxidant with CO and activated organic molecules using O₂(g) while more challenging cases, such as methane to partial oxygenates, relying on H₂O₂. Although H₂O₂ is a green oxidant, the incorporation of dioxygen greatly reduces overall cost and so there is an incentive to find new ways to reduce the reliance on H₂O₂. In this study we use DFT calculations to discuss the direct synthesis of H₂O₂ from H₂(g) and O₂(g) and use this understanding to identify the important surface species derived from dioxygen. We cover the adsorption of oxygen, hydrogen and water to model Au and Pd nanoclusters and the oxidation of the metals, since reduction of any oxides formed will consume H₂. We then turn to the production of a surface hydroperoxy species; the first step in the synthesis of H₂O₂. This can occur via hydrogenation of O₂(ads) with H₂(ads) or via protonation of O₂(ads) by solvent water. Both routes are found to be energetically reasonable, but the latter is likely to be favoured under experimental conditions.