The influences of reducing agents on the structure-activity relationships between oxygen vacancy 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 (Ov) 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 Ov 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 Ov. 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.