Influence of oxidizing and reducing pretreatment on the catalytic performance of CeO2 for CO oxidation

Cerium oxide (CeO2) and ceria-based materials have been extensively investigated as catalyst and support materials for various catalytic reactions, due to higher oxygen storage capacity and excellent redox properties. In the current work, we investigated the impact of pretreatment conditions (e.g., oxidation and reduction) on the physical properties of bulk CeO2 and catalytic activity for CO oxidation as a model reaction. To understand the physical properties of pretreated CeO2 catalysts, a suite of complementary characterization techniques, including X-ray diffraction (XRD), surface area analysis (BET), X-ray photoemission spectroscopy (XPS), and Raman spectroscopy, were applied. The results showed that a higher pretreatment temperature led to a decreased specific surface area (SSA), a decrease in oxygen vacancy/defect sites, and increased crystallite size, while surface Ce3+/Ce4+ ratio did not show a specific relationship to the treatment conditions. The 700 °C treated CeO2 samples under oxidizing and reducing conditions showed higher specific oxidation rate (μmolCO/s/m2) compared to other samples at 280 and 300 °C (or < 15% CO conversion). The CO conversion per total mass of catalysts, however, decreased with increasing temperatures, especially at 700 °C under reducing condition, indicating that the catalytic performance was affected by the physical properties (SSA, oxygen vacancy/defect sites, and crystallite size)..