Oxygen vacancy clusters in bulk cerium oxide and the impact of gold atoms

Ceria is important for catalysis due to its ability to form and utilize oxygen vacancies during redox reactions. Understanding the dynamic formation of the oxygen vacancies has contributed to the development of efficient catalytic processes. Here, we demonstrate the presence of oxygen vacancy clusters in the bulk of ceria and gold/ceria catalysts upon anaerobic carbon monoxide oxidation and describe their interplay with the orbital hybridization of Ce³⁺ 4f and 5d states. Observations are made using in situ X-ray Raman scattering spectroscopy at O K- and Ce N_4,5-edges and in situ X-ray diffraction. These, combined with multiplet calculations, allow detection of the formation of Ce³⁺ in gold/ceria upon low temperature carbon monoxide oxidation. The modifications observed at the O K-edge reflect the rearrangement of the bulk oxygen sublattice. Density-functional theory calculations show vacancy ordering in the bulk, and explain modifications at the O K-edge, involving the hybridization of the Ce 4f and 5d and O 2p orbitals.