Elucidating the structure, redox properties and active entities of high-temperature thermally aged CuOx–CeO2 catalysts for CO-PROX

Abstract

CuO_x–CeO₂ catalysts with different copper contents are synthesized via a coprecipitation method and thermally treated at 700 °C. Various characterization techniques including X-ray diffraction (XRD) Rietveld refinement, N₂ adsorption–desorption isotherms, X-ray photoelectron spectra (XPS), UV-Raman, high-resolution transmission electron microscopy (HRTEM), temperature-programmed reduction (TPR) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) were adopted to investigate the structure/texture properties, oxygen vacancies, Cu–Ce interaction and redox properties of the catalysts. After the thermal treatment, the catalysts exhibited outstanding catalytic properties for the preferential oxidation (PROX) of CO (with the T_50% of 62 °C and the widest operation temperature window of 85–140 °C), which provided a new strategy for the design of Cu–Ce based catalysts with high catalytic performance. The characterization results indicated that moderately elevating the copper content (below 5%) increases the amount of highly dispersed Cu species in the catalysts, including highly dispersed surface CuO_x species and strongly bonded Cu–[O_x]–Ce species, strengthening the Cu–Ce interaction, increasing oxygen vacancies and promoting redox properties, but a further increase in copper content causes the agglomeration of crystalline CuO and decreases the highly dispersed Cu species. This work also provides evidence from the perspective that the catalytic performance of CuO_x–CeO₂ catalysts for CO-PROX at low and high reaction temperatures is dependent on the redox properties of highly dispersed CuO_x species and strongly bonded Cu–[O_x]–Ce species, respectively.