Support and metal particle size effects on platinum and rhodium model catalysts.

摘要

Research focused on the study of support and particle-size effects on the properties of Rh and Pt catalysts. Model catalysts were prepared by evaporation of Rh and Pt onto a series of flat non-porous supports in order to model catalytic properties and simplify the interpretation of experiments. Adsorption properties were studied for Rh on ZrO{dollar}sb2{dollar}(100), Rh on CeO{dollar}sb2{dollar}, Pt on both the Zn- and the O- polar surfaces of ZnO(0001), and Pt on CeO{dollar}sb2{dollar}. Temperature programmed desorption was used to measure the adsorption properties of the catalysts, and catalyst structure was determined for some samples by transmission electron microscopy. In addition, catalytic activities were measured for CO oxidation on Pt/{dollar}alpha{dollar}-Al{dollar}sb2{dollar}O{dollar}sb3{dollar}(0001), Rh/{dollar}alpha{dollar}-Al{dollar}sb2{dollar}O{dollar}sb3{dollar}(0001), and Rh/CeO{dollar}sb2{dollar} and for NO reduction by CO on Rh/{dollar}alpha{dollar}-Al{dollar}sb2{dollar}O{dollar}sb3{dollar}(0001).; Adsorption measurements successfully predicted the particle-size dependence for CO oxidation on Pt/{dollar}alpha{dollar}-Al{dollar}sb2{dollar}O{dollar}sb3{dollar}(0001), the particle-size dependence for NO reduction by CO On Rh/{dollar}alpha{dollar}-Al{dollar}sb2{dollar}O{dollar}sb3{dollar}(0001), and the effect of ceria on CO oxidation over Rh. These results demonstrate the correlation between reaction rates and the adsorption-desorption kinetics of the reactant gases. Studies of Rh/ceria revealed that oxygen from the ceria is able to migrate onto the Rh crystallites, and that this migration is responsible for the enhanced reactivity of Rh/ceria for CO oxidation. This interaction with ceria is metal specific since no oxygen migration was observed from ceria onto Pt. Studies of Rh/ZrO{dollar}sb2{dollar} and Pt/ZnO revealed that metal-support interactions can influence both the adsorption properties and the structure of the supported metal particles. Catalytic properties may also be affected since many reactions are sensitive to the metal morphology.