Roles of Water and H2 in CO Oxidation Reaction on Gold Catalysts

The roles of water (as the representative of H2O and OH) and H-2 in the CO oxidation reaction on a gold surface are thoroughly investigated by density functional theory calculations and microkinetic study. It is found that the key role of water and H-2 is to generate carboxyl species (COOH) by the reaction of CO with OH. The COOH species facilely activate molecular O-2, which is normally considered as the central topic in CO oxidation. The subsequent kinetic study shows that CO oxidation with water is more than a hundred times faster than that without water. The O-2 activation by COOH is a proton transfer reaction which is a superfast one. By the proton transfer, the COOH species not only activate O-2 but also transform unreactive carbonates to H2CO3. Therefore, the roles of water and H-2 are not only to activate molecular oxygen but also to decompose unreactive carbonates. In addition, because OH prefers to react with CO than with H-2, H, or OH, the presence of H-2 should promote CO oxidation but the presence of CO should hinder H-2 oxidation reaction. This work provides novel insights into the role of H2O in CO oxidation and that of H-2 in CO preferential oxidation on gold catalysts.