Multiple Roles of Alkanethiolate-Ligands in Direct Formation of H2O2 over Pd Nanoparticles

Abstract

Coadsorbed organic species including thiolates can promote direct synthesis of hydrogen peroxide from H2 and O2 over Pd particles. Here, density functional theory based kinetic modeling, augmented with activity measurements and vibrational spectroscopy are used to provide atomistic understanding of direct H2O2 formation over alkylthiolate(RS) Pd. We find that the RS species are oxidized during reaction conditions yielding RSO2 as the effective ligand. The RSO2 ligand shows superior ability for proton transfer to the intermediate surface species OOH, which accelerates the formation of H2O2. The ligands promote the selectivity also by blocking sites for unselective water formation and by modifying the electronic structure of Pd. The work rationalizes observations of enhanced selectivity of direct H2O2 formation over ligand-funtionalized Pd nanoparticles and shows that engineering of organic surface modifiers can be used to promote desired hydrogen transfer routes.