Activity of CeO _x and TiO _x Nanoparticles Grown on Au(111) in the Water-Gas Shift Reaction

The high performance of Au-CeO ₂ and Au-TiO ₂ catalysts in the water-gas shift (WGS) reaction (H ₂ O + CO→H ₂ + CO ₂ ) relies heavily on the direct participation of the oxide in the catalytic process. Although clean Au(111) is not catalytically active for the WGS, gold surfaces that are 20 to 30% covered by ceria or titania nanoparticles have activities comparable to those of good WGS catalysts such as Cu(111) or Cu(100). In TiO _{2- x} /Au(111) and CeO _{2- x} /Au(111), water dissociates on O vacancies of the oxide nanoparticles, CO adsorbs on Au sites located nearby, and subsequent reaction steps take place at the metal-oxide interface. In these inverse catalysts, the moderate chemical activity of bulk gold is coupled to that of a more reactive oxide.