Studies of Ru-Cu surfaces were made by applying ultraviolet photoelectron spectroscopy (UPS) to xenon physisorbed on the surfaces. Experiments were conducted on samples prepared by depositing copper on the (001) plane, i.e., the basal plane, of a ruthenium single crystal and on the surface of a ruthenium powder as well. When the amount of copper present on the surface was approximately one-third to one-half of a monolayer, the xenon photoemission spectrum obtained with the ruthenium powder differed significantly from that obtained with a well-annealed, smooth (001) surface plane. The copper appears to form islands on the smooth (001) plane, but on the surface of the ruthenium powder it is not present in this form. Consequently, copper deposited on a smooth (001) plane of ruthenium would not seem to be a good model of a ruthenium-copper catalyst. Introduction of defects into the (001) plane prior to copper deposition yields a surface which corresponds more closely to that of typical catalysts. These findings provide a reasonable way of rationalizing differences observed when studies of the effect of copper on the ethane hydrogenolysis activity of a ruthenium single crystal are compared with studies of the influence of copper on hydrogenolysis activity in actual ruthenium-copper catalysts.
Low lying electronic states of rare gas-oxide anions: Photoelectron spectroscopy of complexes of O − with Ar, Kr, Xe, and N 2 Photoelectron spectroscopy of adsorbed Xe (PAX) was used to characterize various PtlTi0 2 ( 100) surfaces on an atomic scale. The PAX data provide useful information on both geometrical and electronic states of various surface sites. For example, both Ar ion sputtering and high temperature annealing (850°C) in vacuum produce a distribution of (high charge density) surface defect sites, most likely Ti3+ and Ti2+, whose local surface potentials are higher than on a stoichiometric Ti0 2 surface by 0.5 and 1 eV, respectively. Submonolayer deposits of Pt on a stoichiometric Ti0 2 exhibits much lower local surface potentials (0.5-1 eV) than sputterroughened bulk Pt, suggesting modified charge densities at these sites.
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