Catalytic performance and characterization of Au/doped-ceria catalysts for the preferential CO oxidation reaction

The physicochemical properties and catalytic performance in the preferential CO oxidation (PROX) reaction of nanosized gold supported on doped-ceria were investigated. Zn- and Sm-doped Au/ceria catalysts were found to be more active than undoped Au/ceria, whereas the addition of lanthanum oxide had the opposite effect. A reductive pretreatment at 373 K for 1 h promoted catalytic activity. The ability of Au/doped ceria catalysts to tolerate the presence of CO2 and H2O in the feed was also studied. Adding CO2 in the reactant feed provoked a decrease in catalyst activity; however, catalyst doping improved the resistance toward deactivation by CO2. On the other hand, co-addition of CO2 and H2O counteracted the negative effect of CO2, especially in the case of doped samples. IR studies of CO adsorbed at 90 K on the catalysts after different pretreatments gave information on the type of gold species present on the catalyst. The dispersion of gold depended on the nature of the dopant. Au/Zn–CeO2 catalyst demonstrated the greatest dispersion as revealed by HRTEM measurements and comparison of FTIR intensity of the CO adsorption bands on the reduced samples. AuCex clusters were formed on this catalyst by increasing the prereduction temperature. Large amounts of CO2 were produced during the CO–O2 interaction in the presence of a high concentration of zero-valent gold sites on the surface of the modified Au catalysts, confirming their important role in the CO oxidation reaction. IR spectra were collected after exposure to CO + O2 + H2 and also after addition of water in the PROX reaction mixture over Au/Zn–CeO2 at 400 K. The evolution of the FTIR spectra run at 90 K after admission of O2 on preadsorbed CO on the most active catalyst (i.e., Au/Zn–CeO2) demonstrates the roles of the highly dispersed gold and the reduced support in activating oxygen.