The influence of reducing agents on structure–activity relationships between oxygen vacancies and Au sites for CO preferential oxidation†

Ceria (CeO₂)-based gold (Au) catalysts exhibit remarkable catalytic performance for preferential oxidation of CO in an H₂-rich stream (CO-PROX), and their activity can be further enhanced by defect engineering and regulation of Au sites. Herein, oxygen vacancies (O_v) were constructed on CeO₂ using different reducing agents, including H₂, NaBH₄ and ascorbic acid, to modulate the electronic structure and coordination environment of Au sites. The properties of O_v and Au species were investigated by a series of characterization methods, such as electron paramagnetic resonance (EPR), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The results of catalytic tests for CO-PROX showed that the sample reduced by H₂ at 400 °C (Au/CeO₂-H₂-400) achieved the best performance, which completely converted CO across a wide temperature window, ranging from 70 °C to 150 °C, while maintaining satisfactory selectivity and stability. The superior performance was attributed to the fact that, unlike ascorbic acid and NaBH₄, H₂ is a small molecule with negligible steric hindrance, leading to a more concentrated distribution of O_v. These vacancies promoted the formation of partially oxidized Au⁺ with a moderate Au–O coordination number, which enhanced CO adsorption and facilitated the activation of lattice oxygen, thereby contributing to the exceptional catalytic activity.