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

摘要

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.1R 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.AuCe_x 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.