Study of H-2, O-2, CO adsorption and CO+O-2 reaction on Pt(100), Pd(110) monocrystal surfaces

Nanoscale changes in the surface morphology of Pd particles that accompany the uptake of hydrogen have been studied in situ by Field Electron Microsco py (FEM). Exposure of a Pd tip to H-2 at low temperatures led to the format ion of extruding PdHx particles on top of the Pd tip. Growth of these parti cles proceeds in a "staccato'' manner. When most of the hydrogen have been removed from the sample by heating in vacuum, Pd crystallites remain on the surface. They are quite stable up to about 700 K, where they melt back int o die bulk of the tip. A sharp low temperature H-2-peak (220 K) appears in the TD spectra as a result of decomposition of PdHx hydrides on Pd(110) sin gle crystal surface. During the O-2 + H-ads reaction, a hydrogen-modified P t(100)-(hex) surface shows an increase in the population of atomic oxygen s tates: three O-ads states are observed by high resolution electron energy l oss spectroscopy (HREELS) as a result of the presence of defect sites. The reactivity of these new oxygen states to CO has been investigated with ther mal desorption spectroscopy (TDS). (C) 2000 Elsevier Science B.V. All right s reserved.