Active Sites and Interfacial Reducibility of CuO/CeO₂ Catalysts Induced by Reducing Media and O₂/H₂ Activation

The development of a highly efficient and stable catalyst for preferential oxidation of CO for the commercialization of proton-exchange membrane fuel cells has been a result of continuous effort. The main challenge is the simultaneous control of abundant active sites and interfacial reducibility over the catalyst CuO/CeO₂. Here, we report a strategy to modulate porosity, active sites, and O-vacancy sites (O_V) by reducing media and O₂/H₂ activation. O₂-pretreated CeO₂-supported Cu catalysts unequivocally demonstrate the low-temperature activity owing to the excess concentrations of Cu⁺ and Cu²⁺ as well as the relative population of Ce³⁺ and O-vacancy sites at the surface. O₂ activation improves the Cu²⁺ diffusion into the CeO₂ lattice to generate the synergistic effect and induces the formation of electron-enriched Cu²⁺-O_V-Ce³⁺ sites, which accelerate the activation and dissociation of CO/O₂ and the formation of reactive oxygen species during catalysis. Density function theory (DFT) calculations reveal that CO adsorbs on Cu₂O {110} and CuO {111} with relatively optimal adsorption energy and longer C-Cu lengths in contrast to that on Cu {111}, favoring the adsorption and desorption of CO. These are crucial for ongoing CO oxidation, producing CO₂ by the Mars-van Krevelen mechanism.