STRUCTURAL CHARACTERIZATION AND CATALYTIC BEHAVIOR OF AL2O3-SUPPORTED CERIUM OXIDES

Three kinds of supported cerium oxide catalysts were prepared by an impregnation and a sol gel technique using aluminium tri-isopropoxide (AIP) and cerium(III) nitrate dissolved in ethylene glycol. One is cerium dioxide supported on alumina, and others are finely-divided nonstoichiometric cerium oxide and cerium aluminate crystallites dispersed on alumina, respectively. In order to investigate the relationship between the structure of cerium oxides and their catalytic behavior, these cerium oxides were subjected to ''OSC'' (oxygen storage capacity) measurements as well as kinetic studies for methane oxidation. The highest ''OSC'' was achieved on the finely-divided nonstoichiometric cerium oxides. Kinetics studies for methane oxidation resulted in the first order with respect to methane for all the catalysts, and nearly zero order with respect to oxygen on the cerium dioxide and cerium aluminate. While on the finely-divided nonstoichiometric cerium oxides a half order with respect to oxygen was obtained. On the basis of these results the structure and the catalytic behavior of cerium oxides was discussed in terms of the ''OSC'' associated with the oxygen vacancies existed in the finely-divided nonstoichiometric cerium oxides. A brief discussion was also made on Pd catalysts supported on these cerium oxides for methane oxidation.