Electronic Structural Modulation for CO–CO₂ Conversion of Copper-Modified Nanoceria Studied by In Situ X-ray Absorption Spectroscopy

Metal-supported cerium dioxide catalysts are widely used in industrial processes. This study investigates copper-cerium dioxide (Cu-CeO₂) as a promising catalyst for CO oxidation, noted for its cost-effectiveness and low activation temperature. However, the reaction mechanism remains unclear. We examine the effects of copper ion doping into CeO₂ nanoparticles at 0, 5, 15 at%, synthesized via precipitation. X-ray diffraction (XRD) analysis confirmed sample purity, revealing partial amorphization at a higher doping level. Lower Cu concentration in CeO₂ facilitated CO oxidation at a lower temperature. X-ray absorption spectroscopy (XAS) investigated the electronic and atomic structures, showing that CeO₂ with a lower Cu doping resulted in a higher lattice oxygen content and moderate Cu ion reduction. Increased Cu doping decreased Ce-O coordination numbers, while Cu-O radial distance was larger at lower doping. In situ XAS identified moderate reduction of Ce and Cu, elucidating CO oxidation via the Langmuir-Hinshelwood (LH) mechanism at lower Cu concentration. The superior low-temperature CO oxidation performance is attributed to moderate Ce and Cu ion reduction coupled with increased oxygen adsorption on the catalyst surface. These findings provide insights into the relationship between the dopant concentration, electronic structure, and catalytic activity for optimizing ceria-based catalysts for efficient CO oxidation.