Steam activation significantly promotes the CO oxidation performance of Pt/CeZrO₂ catalyst: Enhancement effect and mechanism

CO oxidation reaction has important industrial significance in controlling automotive exhaust emissions, however, the effect of steam on the activity of ceria-zirconia solid solutions supported catalyst is still unclear. In this study, ceria-zirconia solid solutions were prepared by the traditional co-precipitation method (CZO) and the novel ammonium carbonate etching method (CZOe). After loading 1 wt% Pt, the synthesized Pt/CZOe and Pt/CZO catalysts were characterized comprehensively by XRD, HAADF-STEM, XPS, DRIFTS, and Raman spectroscopy, the results suggested that the Pt species were uniformly dispersed as Pt2+ single sites. Both Pt/CZOe and Pt/CZO catalysts could be activated under wet conditions and showed improved CO oxidation activity compared to dry conditions, especially the CO complete conversion temperature (T-100) of Pt/CZOe decreased by 100 degrees C. Furthermore, the enhancement mechanism of steam on the catalysts has been deeply studied using in-situ CO DRIFTS spectra analysis and O-18 isotope labeling experiments, which indicated that H2O molecules were adsorbed and dissociated on the surface of the catalysts, forming terminal Ce-OH bonds that facilitated the reaction rate. The Pt/CZOe catalyst showed a remarkable enhancement of low-temperature CO oxidation activity under wet conditions compared to the Pt/CZO catalyst due to the outstanding porosity which facilitates the adsorption of H2O molecules. In the (H2O)-O-18-involved experiments, the formation of (CO2)-O-18 and (COO)-O-18-O-16 and the appearance of the (CO)-O-18-Pt2+ band demonstrated that H2O molecules participated in the reaction directly as reactants, the CO bond of CO molecules adsorbed on Pt could be broken and replaced by hydroxyl oxygen of adjacent Ce-OH. The present work revealed the enhancement effect and mechanism of steam on the CO oxidation performance of ceria-zirconia solid solutions supported catalyst, and the research methods and results in this work have important reference significance for the activation research of other catalysts.