Theoretical study of the direct synthesis of H₂O₂ on Pd and Pd/Au surfaces

The direct synthesis of hydrogen peroxide on Pd and Pd/Au catalysts was investigated with first-principle DFT methods for periodic two-dimensional surfaces. A two-step reaction mechanism was proposed starting from a superoxo precursor state of the dioxygen molecule on Pd surface and its subsequent reaction with two hydrogen atoms situated over neighboring 3-fold positions. A competitive reaction of dioxygen dissociation leading to the nonselective formation of water was found. We have shown that the presence of surface gold atoms blocks this dissociation and increases the selectivity toward the main product, H₂O₂, which explains the experimentally reported data.