Structure and oxidation state of gold on different supports under various CO oxidation conditions

The structure of gold clusters of different sizes supported on various metal oxides (Al2O3, TiO2, SiO2) exposed to different CO oxidation conditions was investigated in situ using X-ray absorption spectroscopy at the Au L3 edge. In all catalysts, the only phase detected during catalysis was Au0. In the most active sample with small gold particles (Au/Al2O3), variation in the electronic structure of the gold clusters with changing reaction conditions was observed by XANES spectroscopy and ascribed to the adsorption of CO on the metallic gold clusters. FEFF8 calculations proved that the changes in the XANES signature of Au/Al2O3 can be explained by backdonation of d-electrons into the π∗π∗ orbitals of CO. For Au/Al2O3, the presence of AuO backscattering in the EXAFS suggested weak cluster–support interactions. For Au/SiO2 and Au/TiO2, the structure of the gold clusters remained unchanged throughout all experiments.