Total oxidation of propene over Au/xCeO2-Al2O3 catalysts: Influence of the CeO2 loading and the activation treatment

This study explores the reaction of oxidation of propene (1200 ppm) under excess oxygen (9%) over Au/xCeO2/Al2O3 catalysts (x = 1.5, 3, 5, and 10 wt% CeO2) to mimic the conditions of VOC decomposition. The present study reveals the influence of several factors that affect the oxidative performance of the Au/xCeO2/Al2O3 catalysts, such as the ceria loading, the catalyst activation method, i.e., the gold oxidation state, the gold particle size and the distribution of gold on ceria and alumina. The Au/xCeO2/Al2O3 catalysts were found 100% selective to CO2. Their activity was intermediate between that of Au/Al2O3 (poorly active) and Au/CeO2 (active). Interestingly, the activity increased with the ceria loading when the samples were activated under H2 at 300 °C, but decreased when they were activated under O2 at 500 °C. Characterization of the Au/xCeO2/Al2O3 catalysts after both types of activation was performed by TEM, EFTEM, XPS and CO oxidation reaction. The results show that whatever the mode of activation, as the CeO2 loading increased, the proportion of gold particles on alumina decreased while that on ceria increased, but gold remained unreduced on ceria after calcination under O2 whereas it was metallic after reduction under H2. Gold on ceria being more active when it is metallic than when it is unreduced, this explained the evolution of the catalytic results of propene oxidation as the ceria loading varied.