Oxygen Storage Capacity of Alumina-supported Rh/CeO₂ Catalyst

Abstract

One is a subsequent impregnation of alumina with an aqueous solution containing Ce ions and then with that containing Rh ions. The other method is a mixing of CeO₂/Al₂O₈ with Rh/Al₂O₂ so that the Rh: CeO₂ ratio is same as the ratio in the impregnated catalyst. The intimate contacts between rhodium and cerium oxide particles are much more expected in the former catalyst. In ord er to estimate the Oxygen Storage Capacity (OSC) values the catalysts were completely oxidized by injection of oxygen pulses, followed by cyclic pulses of oxygen and hydrogen until the consumptions of both gases on the catalyst were constant. The OSC of cerium oxide in the Rh/CeO₂/Al₂O₃ catalyst was found to be greater than that of the physically mixed catalyst, indicating that the intimate contacts between rhodium and cerium oxide particles dispersed on alumina play an important role for the OSC of cerium oxide in the catalyst. Because of these intimate contacts, hydrogen and oxygen activated on the surface of rhodium particles are easy to spill over the neighboured cerium oxide particles to react with lattice oxygens and oxygen vacancies in the ceria crystallites. Thus, the intimate contacts between rhodium and cerium oxide particles are essential for the enhanced OSC of cerium oxide.