Understanding and application of metal-support interactions in catalysts for CO-PROX

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 (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.

Different metal (Mn, Fe, Co, Ni, and Zr) decorated Cu/CeO2 catalysts for efficient CO oxidation in a rich CO2/H2 atmosphere

In this work, CuM/CeO2 (M = Mn, Fe, Co, Ni, and Zr) catalysts with a low Cu content of 1 wt% were purposely designed and prepared using the co-impregnation method. The samples were characterized using various techniques (TG-DTA, XRD, N2-adsorption/desorption measurements, H2-TPR, XPS and Raman spectroscopy) and CO preferential oxidation (CO-Prox) under H2/CO2-rich conditions was performed. The results have shown that enhanced catalytic performance was achieved upon the introduction of Mn, Co and Ni, and little impact was observed with Zr doping, but Fe showed a negative effect, as compared with the Cu/CeO2 catalyst. Characterization data revealed that the M doping strongly changed the surface composition, revealing the decreased Cu/Ce ratios on the surface, which could be accounted for by the formation of more M/Cu-O-Ce solid solution, or strong Cu-M interactions. When Mn was used, the obtained CuMn/CeO2 catalyst revealed the highest concentration of the oxygen vacancies and Ce3+ ions, which could be correlated well with its superior catalytic performance. Compared with the Cu/CeO2 catalyst, the CO conversion rate increased by 24.7% at a low temperature of 90 °C over the CuMn/CeO2 catalyst. At 130 °C, the maximum CO conversion was 94.7% and the CO2 selectivity was 78.9%. Conversely, the Fe doped Cu/CeO2 catalyst demonstrated the poorest catalytic activity, which was due to the blockage effect of Fe species on Cu showing a high Fe/Cu ratio of 1.9 on the surface.