STRUCTURAL CHARACTERIZATION AND CATALYTIC BEHAVIOR OF AL2O3-SUPPORTEDCERIUM OXIDES

Three kinds of supported cerium oxide catalysts were prepared by an im pregnation and a sol gel technique using aluminium tri-isopropoxide (A IP) and cerium(III) nitrate dissolved in ethylene glycol. One is ceriu m dioxide supported on alumina, and others are finely-divided nonstoic hiometric cerium oxide and cerium aluminate crystallites dispersed on alumina, respectively. In order to investigate the relationship betwee n the structure of cerium oxides and their catalytic behavior, these c erium oxides were subjected to ''OSC'' (oxygen storage capacity) measu rements as well as kinetic studies for methane oxidation. The highest ''OSC'' was achieved on the finely-divided nonstoichiometric cerium ox ides. Kinetics studies for methane oxidation resulted in the first ord er with respect to methane for all the catalysts, and nearly zero orde r with respect to oxygen on the cerium dioxide and cerium aluminate. W hile on the finely-divided nonstoichiometric cerium oxides a half orde r with respect to oxygen was obtained. On the basis of these results t he 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 discuss ion was also made on Pd catalysts supported on these cerium oxides for methane oxidation.