Dynamic Role of Gold d-Orbitals during CO Oxidation under Aerobic Conditions

High-energy-resolution fluorescence detection-X-ray absorption near-edge structure (HERFD-XANES) at the Au L3 edge was used to study gold catalysts supported on ceria in order to unravel the role of gold 5d orbital modifications during the activation of molecular oxygen. The variations in the HERFD-XANES resonance peak, which are directly correlated with the d-band occupancy, were monitored in situ during the redox process of the CO oxidation at room temperature under both aerobic and anaerobic conditions. Interestingly, upon the oxidation treatment and also during the aerobic CO oxidation treatment, the gold d-band fluctuates around an average value, proving that the gold clusters are partially charged. The dynamism of the gold electronic configuration was evidenced by a temporary variation of the gold d-orbital population during the oxidation reaction. The interpretation of X-ray spectroscopy data is supported by ab initio simulations performed using the FDMNES code.