MODEL CATALYSTS - FROM EXTENDED SINGLE-CRYSTALS TO SUPPORTED PARTICLES

Model oxide-supported metal catalysts have been prepared by evaporating a metal (e.g., Cu, Pd) onto an oxide (SiO2,Al2O3) thin film (similar to 100 Angstrom) which, in turn, is supported on a refractory metal (Mo, W, Ta) surface. The deposited metal films, upon annealing, form small metallic clusters on the oxide surface whose sizes are dependent upon the initial metal film thickness. The surface structures and particle morphologies have been characterized using scanning probe microscopies, temperature programed desorption, X-ray and ultraviolet photoemission, and high-resolution electron energy-loss spectroscopy/infrared reflection-absorption spectroscopy of adsorbed carbon monoxide. The catalytic properties of these particles have also been investigated with respect to several reactions including CO/O-2 and CO/NO. The chemical and electronic properties of the metal particles with respect to size are compared to the analogous properties of extended single-crystal surfaces.