Site Communication in Direct Formation of H₂O₂ over Single-Atom Pd@Au Nanoparticles

Single atom alloy catalysts offer possibilities to obtain turnover frequencies and selectivities unattainable by their monometallic counterparts. One example is direct formation of H₂O₂ from O₂ and H₂ over Pd embedded in Au hosts. Here, a first-principles-based kinetic Monte Carlo approach is developed to investigate the catalytic performance of Pd embedded in Au nanoparticles in an aqueous solution. The simulations reveal an efficient site separation where Pd monomers act as active centers for H₂ dissociation, whereas H₂O₂ is formed over undercoordinated Au sites. After dissociation, atomic H may undergo an exothermic redox reaction, forming a hydronium ion in the solution and a negative charge on the surface. H₂O₂ is preferably formed from reactions between dissolved H⁺ and oxygen species on the Au surface. The simulations show that tuning the nanoparticle composition and reaction conditions can enhance the selectivity toward H₂O₂. The outlined approach is general and applicable for a range of different hydrogenation reactions over single atom alloy nanoparticles.