Behaviour of oxygen species adsorbed on Al2O3-supported cerium oxide catalysts for methane oxidation

The properties and catalytic behaviour of adsorbed oxygen species on alumina-supported cerium oxides (CeO2, CeAlO3 and CeO2-x) for methane oxidation have been investigated by means of EPR, FTIR, temperature-programmed desorption (TPD) and O-18 tracer techniques. The adsorbed oxygen on the cerium oxide catalysts was found to be the side-on type O-2(-) ion by EPR and FTIR measurements. The adsorption site of the O-2(-) ion on CeO2-x/Al2O3 was assumed to be the site formed by the ensemble effect between oxygen vacancies and surface cations, while on the other catalysts the sites were cerium ions on the surface. The oxygen species desorbed after O-18(2) adsorption at 773 K were O-16(2) and O-16 O-18 in all catalysts, and the major products for methane oxidation were (CO2)-O-16 and (CO)-O-16 O-18. These suggest that the adsorbed oxygen is activated through the lattice in cerium oxides. The activities of methane oxidation were influenced by the oxygen diffusion processes on the cerium oxides.