Binding of Oxygen on Single-Atom Sites on Au/Pd(100) Alloys with High Gold Coverages

Oxygen adsorption was studied on a Au/Pd(100) single crystal as a model for single-atom-alloy catalysts since the surface contains isolated palladium atoms surrounded by gold at high gold coverages, and density functional theory calculations show sharp, atomlike palladium electron density of states, typical of single-atom alloy systems. Since O2 does not adsorb dissociatively on these high-gold-coverage alloys, atomic oxygen was dosed using ozone. The strength of oxygen adsorption was investigated by temperature-programmed desorption experiments on substrates with different gold coverages. Kinetic Monte Carlo simulations were used to determine the desorption activation energies from the experiments, which correlated well with the results of density functional theory calculations. These calculations also enabled the adsorbate energy levels to be identified. It has been proposed that adsorbate binding and reactivity are dominated by the atomlike states, but no simple atomlike quantum theory models could successfully describe the energy-level locations. However, good correlations were found between the binding energy and location of the d-band center, implying that the adsorbate interacts with the extended substrate energy bands rather than with a single localized state of the active component. Similar calculations were performed for a molecular system comprising molecular oxygen on the alloy with similar conclusions and where the O2 binding energy also correlates well with the d-band center energy.