EVIDENCE FOR A 2ND CO OXIDATION MECHANISM ON RH CERIA

The reaction properties of ceria-supported Rh for CO oxidation were investigated using model catalysts prepared by vapor deposition of Rh onto flat, low-surface-area ceria. Steady-state reaction rates were measured on this catalyst at 573 K for O2, pressures between 0.1 and 8 Torr and for CO pressures between 0.1 and 600 Torr, and the rates were compared to those measured on Rh/α-Al2O3(0001). The rates for Rh/ceria and Rh/α-Al2O3(000l) are essentially identical over most of the pressure range studied, with the reaction order for CO being inverse first-order under reducing conditions. However, for higher CO pressures, the reaction becomes zeroth-order in CO on Rh/ceria. It is suggested that this is due to a second reaction mechanism involving oxygen migration from ceria to the Rh, which had previously been observed in temperature-programmed desorption measurements on the same model catalysts (Zafiris, G. S., and Gorte, R. J., J. Catal.139, 561 (1993)). © 1993 Academic Press, Inc.