Anionic Single-Atom Catalysts for CO Oxidation: Support-Independent Activity at Low Temperatures

We study 14 atomically dispersed transition metals on halite-type oxides (MeO, Me = Fe, Mg, Mn, and Ni) using periodic density functional theory calculations and probe structure and activity toward CO oxidation for a subset of these systems experimentally. Pd and Pt can form stable negatively charged species upon binding to oxygen vacancies; the magnitude of the metal atom binding energy depends on the O vacancy formation energies of the supporting metal oxide and the lattice match between transition metal and support. The resulting oxide-supported single-atom systems catalyze CO oxidation by molecularly adsorbed O-2 with intrinsic barriers as low as 36 kJ/mol for Pt/MnOx(001). This high activity stems from the single sites' ability to stabilize surface superoxide species. Furthermore, intrinsic barriers were found to depend primarily on the identity of the transition metal and to be nearly independent of the support identity. However, O-2 may heal the oxygen vacancy, which leads to catalyst deactivation. Catalyst deactivation by oxygen can be suppressed by using a more reducible support such as FeO(001) or MnO(001).