Role of Water in CO Oxidation on Gold Catalysts

Gold nanoparticles supported on base metal oxides exhibit high catalytic activity in the low temperature oxidation of CO. Numerous studies have been carried out by using powder, single crystal, and planar model catalysts together with density functional theory calculations to elucidate the reaction mechanism and the nature of the active sites. A characteristic feature of these catalysts is that the moisture contained in the catalyst and in the reactant gas markedly enhances CO2 formation rates. The promoting role of moisture, which is advantageous for the practical applications to air purifiers, can be classified into four categories: (i) maintain cationic state of gold (Au3+ or Au+), (ii) direct involvement of H2O and OH- groups in CO oxidation, (iii) activation of O-2 molecules, and (iv) transformation of catalytic intermediates and inhibitors (spectators) such as carbonate species. The elucidation of the role of water in CO oxidation will deepen the understanding of the unique catalysis by gold.