| The steady-state kinetic studies of ceria-supported metal catalysts were investigated to gain a better understanding of oxygen storage in three-way catalysts. First, CO oxidation kinetics on Rh/ceria, Pd/ceria and Pt/ceria catalysts suggest that there are two mechanisms in excess CO. The first one is identical to that observed on pure metal. The second one, which appears to involve a reaction of oxygen from ceria with CO from metal, becomes more important for smaller metal particle sizes, high CO pressures, and low temperatures, and is independent of metals.; For ceria and ceria-zirconia, deactivation, through the loss of the second mechanism, caused by high-temperature calcination, was investigated, with Pd added after calcination so that the metal particle size remained the same and did not contribute to deactivation. For ceria, there was a strong dependence on calcination temperature with almost complete loss of the second mechanism above 1170K. Results for ceria-zirconia, however, showed that the loss in this case was more gradual, with CO oxidation activity due to the second mechanism maintained to much higher calcination temperatures.; The steady-state, water-gas-shift kinetics studies on ceria-supported, Pd, Pt and Rh catalysts show identical rates for each of the metals. Similar to CO oxidation rates, the water-gas-shift rates strongly depend on ceria structure. I propose that water-gas-shift on ceria-supported metals occurs through a bifunctional mechanism in which CO adsorbed on the metals is oxidized by ceria, which in turn is oxidized by water. Deactivation of the catalyst following growth in the ceria crystallite size is due to the decreased reducibility of large ceria crystallites.; The Transmission Electron Microscopy experiments show the formation of ceria crystallites from the initially amorphous ceria film, after calcining at 670K. Annealing to 870K causes the crysyallites to grow; however, no ordering of the ceria crystallites with respect to the zirconia substrate was found. After calcining at 970K, some of the ceria films started having a preferential orientation with respect to zirconia. |
