Coadsorption of carbon monoxide and hydrogen on a Ni(111) surface: Influence of the "surface carbide"

Abstract

Vibrational electron energy loss spectroscopy (HRELS) combined with LEED, work function changes and thermodesorption measurements have been used to study H2CO interactions on a Ni(111) surface. Coadsorption of H2 and CO on a Ni(111) surface, maintained at 140°C and then cooled down to room temperature, under the reactional mixture, leads to the appearance of three surface species: (a) a weakly bonded CO thermally desorbed around 75°C and exhibiting a ν-C0 frequency loss peak near 221 meV; (b) an oxyhydrocarbonated compound characterized by vibrations at 362, 178 and 168 meV and by simultaneous desorption of H2 and CO at 180°C; (c) a hydrocarbonated species which dehydrogenates at 280°C and exhibits vibrations at 376 and 95 meV. Since disproportionation of CO occurs at 140°C and leaves the so called "surface carbide" behind, it is possible that this carbide plays an important role in the formation of the observed surface species. In fact, coadsorption of CO and H2, at room temperature on a carburized Ni(111) surface, allows the appearance of the weakly bonded CO in addition to the oxyhydrocarbonated species. Nevertheless, the third species (hydrocarbonated) is then not observed. Tentative identification of the different surface complexes is developed by reference to their vibrational spectra. © 1979.