H₂O Dissociation at the Perimeter Interface between Gold Nanoparticles and TiO₂ Is Crucial for Oxidation of CO

To clarify the role of H₂O in the oxidation of CO over Au/TiO₂ at low temperatures (<320 K), we conducted a temperature-programed desorption analysis of the reactivity of H₂O with Au nanoparticles deposited on single-crystal TiO₂(110) surfaces. Two desorption peaks were observed: a peak at 370 K was attributed to molecular desorption of H₂O, and a peak at 510 K was attributed to recombinative desorption of H₂O. The amount of dissociated H₂O adsorbed on the Au/TiO₂(110) surface increased in inverse proportion to the second power of the mean Au particle diameter in the range of 1-10 nm and increased linearly with increasing perimeter length around the Au particles, indicating that H₂O dissociates to H and OH at the perimeter interface between the Au and TiO₂. We also found that the H₂O dissociation reaction and the oxidation of CO proceeded at the same active sites. We believe that the oxidation of CO is initiated by the dissociation of H₂O. The obtained results provide a deeper experimental insight on a role of H₂O in the oxidation of CO over Au/TiO₂ catalysts.