Oxygen storage capacity (OSC) and active oxygen species of alumina-supported nonstoichiometric cerium oxide catalysts

Structural effect and oxygen storage capacity (OSC) on alumina-supported cerium oxide catalysts have been studied. The behavior and activity of active oxygen species originated from OSC also have been characterized. In those catalysts, the catalyst prepared by an alkoxide method using needle boehmite sol derived from aluminum tri-isopropoxide (AIP) and cerium nitrate dissolved in ethylene glycol gave a finely-divided nonstoichiometric cerium oxide dispersed on alumina (CeO2-x/Al2O3) after the H-2 reduction at 900 degrees 0. The presence of a finely-divided nonstoichiometric cerium oxide containing Ce3+ and Ce4+ ions was anticipated by XRD, EXAFS and fluorescent measurements. The higher OSC was achieved on CeO2-x/Al2O3 catalyst, compared with CeO2/Al2O3 and CeAlO3/Al2O3 where cerium oxides were stoichiometric structures. It was concluded by O-18 tracer studies that the higher activity of CeO2-x/Al2O3 catalyst for methane oxidation was mainly associated with the activation sites of oxygen species, where the sites consisted of oxygen vacancies formed by finely-divided nonstoichiometric structures, from the surface to the bulk and vice versa. The addition of palladium to CeO2-x/Al2O3 catalyst enhanced drastically the OSC and improved the catalytic activity on NO decomposition by the acceleration of oxygen spillover, indicating the generation of synergetic effect between Pd and CeO2-x. The good relation between OSC and NO decomposition activity on Pd/CeO2-x/Al2O3 catalyst might promise the preparation of new catalyst by the control of OSC.