CO oxidation studies over cluster-derived Au/TiO₂ and AUROlite™ Au/TiO₂ catalysts using DRIFTS

Thiol-ligated Au₃₈(SC₁₂H₂₅)₂₄ clusters were synthesized and supported on a microporous TiO₂ support by incipient wetness impregnation. After a reductive pretreatment designed to remove the thiol ligands, the activity of catalyst was tested using CO oxidation in a fixed-bed reactor at 30 and 60°C. CO oxidation was also performed at similar conditions in an in situ FTIR (DRIFTS) cell to monitor the species that were formed during the reaction, and results were compared to commercially available Au/TiO₂ catalyst. Our Au/TiO₂ was less active than this commercial catalyst for CO oxidation, likely due to the presence of bidentate carbonate species. DRIFTS studies on the commercial catalyst showed strong peaks at 1718 and 1690 cm^-1 that are not present in our catalyst. We propose that these bands are due to bridging CO₂ between AuTi and AuAu centers formed via direct oxygen atom transfer from the titania surface to AuCO. On the surface of our catalyst, however, a different reaction mechanism involving sulfur-mediated oxygen transfer at the Au-TiO₂ interface has been proposed.