Water adsorption on clean and oxygen covered Pd(100) has been studied by electron energy loss spectroscopy and low energy electron diffraction. On the clean surface water is associatively adsorbed and reveals hydrogen bonding. Hydroxyl is produced upon water adsorption on oxygen precovered Pd(100). The hydroxyl molecule is adsorbed with its molecular axis significantly tilted away from the surface normal. A study of the reactivity of coadsorbed hydrogen and hydroxyl yields new information on the catalytic oxidation of hydrogen on Pd(100). The following reaction path could be inferred: Oad+Had→OHad, 2OHad→Oad+H2Oad→Oad+H2Og.
We report the observation of molecular H2 chemisorption at the edge sites of a stepped Ni (100) surface that is covered with a dense layer of atomic hydrogen. No such state is observed on the flat Nl (100) surface. We suggest that this H2 chemisorption state can form stably as a result of residual unfilled d states at these step sites, while the dissociative channel is blocked by the saturated atomic adsorbate layer.
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