Pinpointing the catalytic role of water in low-temperature CO oxidation on gold catalysts at a molecular level

Water substantially promotes the low-temperature redox reactions catalyzed by gold. However, clarifying the catalytic role of water is challenging due to co-existing OH and H2O species on Au catalysts under working conditions. Here, via controlled preparation of OH and adsorbed H2O species on a NiO/Au(111) inverse model surface combined with isotope-labelling reactants, we provide unambiguous spectroscopic experimental evidence to identify adsorbed H2O species, instead of OH groups, to promote O2 activation for low-temperature CO oxidation at the NiO-Au interface. In combination with theoretical calculations, adsorbed H2O-stabilized O2 species was found to be facilely activated into reactive OOH species but OH stabilized-O2 species could not. These results further discriminate the role of adsorbed H2O species and OH group in O2 activation in gold catalysis, which significantly advances our fundamental understanding of both Au catalysis and catalytic role of H2O.