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

Abstract

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 CO 2 and H 2O in the feed was also studied. Adding CO 2 in the reactant feed provoked a decrease in catalyst activity; however, catalyst doping improved the resistance toward deactivation by CO 2. On the other hand, co-addition of CO 2 and H 2O counteracted the negative effect of CO 2, 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–CeO 2 catalyst demonstrated the greatest dispersion as revealed by HRTEM measurements and comparison of FTIR intensity of the CO adsorption bands on the reduced samples. AuCe x clusters were formed on this catalyst by increasing the prereduction temperature. Large amounts of CO 2 were produced during the CO–O 2 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 + O 2 + H 2 and also after addition of water in the PROX reaction mixture over Au/Zn–CeO 2 at 400 K. The evolution of the FTIR spectra run at 90 K after admission of O 2 on preadsorbed CO on the most active catalyst (i.e., Au/Zn–CeO 2) demonstrates the roles of the highly dispersed gold and the reduced support in activating oxygen.