Surface spectroscopic characterization of oxide thin films and bimetallic model catalysts

Abstract

Oxide thin films and bimetallic model catalysts have been studied using metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS), low energy ion scattering spectroscopy (LEISS), X – ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD) under ultra high vacuum (UHV) conditions. Of particular interest in this investigation was the characterization of the surface morphology and electronic/geometric structure of the following catalysts: SiO2/Mo(112), Ag/SiO2/Mo(112), Au–Pd/Mo(110), Au–Pd/SiO2/Mo(110), and Pd– Sn/Rh(100). Specifically, different types of oxide surface defects were directly identified by MIES. The interaction of metal clusters (Ag) with defects was examined by work function measurements. On various Pd related bimetallic alloy surfaces, CO chemisorption behavior was addressed by IRAS and TPD. Observed changes in the surface chemical properties during the CO adsorption-desorption processes were explained in terms of ensemble and ligand effects. The prospects of translating this molecular-level information into fundamental understanding of ‘real world’ catalysts are discussed.