AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoA

Paper SS2-MoA6
Carbon-Sulfur Bond Activation in Adsorbed Methylthiolate on Ni(100) with Gas Phase Atomic Hydrogen at 120 K

Monday, November 2, 1998, 3:40 pm, Room 309

Session: Surface Chemistry on Model Catalysts
Presenter: A.T. Capitano, University of Michigan
Authors: A.T. Capitano, University of Michigan
J.L. Gland, University of Michigan
Correspondent: Click to Email
Low temperature carbon-sulfur bond activation has been observed during reaction with both gas phase atomic and subsurface hydrogen. These results show for the first time that hydrogen can directly induce C-S bond activation in an adsorbed species. This new surface reaction provides exciting new opportunities for examining fundamental mechanisms of hydrodesulfurization on surfaces under UHV conditions. Gas phase atomic hydrogen breaks the C-S bond in methylthiolate resulting in the formation of methane even at 120 K on the Ni(100) surface. These results indicate that the energy for C-S bond activation is furnished by the atomic hydrogen. In contrast, coadsorbed hydrogen causes no C-S bond activation in methylthiolate. For a constant flux of gas phase atomic hydrogen, the rate of methane formation is first order in methylthiolate coverage indicating a direct Eley-Rideal reaction. Some adsorbed methyl and methylthiolate can remain on the surface after reaction, depending on atomic hydrogen exposure. During subsequent TPD experiments, addition of hydrogen to these intermediates results in three methane formation processes. Subsurface hydrogen breaks the C-S bond in methylthiolate at 200 K. Methyl hydrogenation by coadsorbed hydrogen occurs at 250 K. Or, thermal activation of the C-S bond by the surface is observed at 320 K. Taken together, these results demonstrate that energetic forms of hydrogen can break C-S bonds by direct addition to adsorbed thiolates on metal surfaces. The new mechanistic information generated using this approach may have substantial implication in fields ranging from catalytic hydrodesulfurization to stability of microelectronic devices.