AVS 45th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS2-TuA

Paper SS2-TuA8
The Reactivity of Surface Defects on the MoS@sub 2@(0001) Basal Plane: Methanethiol and Thiophene Reactivity Studies

Tuesday, November 3, 1998, 4:20 pm, Room 309

Session: Morton M. Traum Student Award Session
Presenter: C.G. Wiegenstein, Michigan Technological University
Authors: C.G. Wiegenstein, Michigan Technological University
K.H. Schulz, Michigan Technological University
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Molybdenum disulfide based materials are important industrial catalysts for the removal of aromatic organosulfur compounds from petroleum feedstocks. The removal of sulfur compounds is important since sulfur is a known catalysts poison. Although there have been significant amounts of study on the structure of the industrial hydrodesulfurization catalysts, there is still a significant amount of uncertainity as to the surface chemistry and reactivity of the organosulfur compounds on the catalyst surface. Information on surface intermediates and adsorbate structures is hindered by the high pressures used in commercial HDS reactors. MoS@sub 2@ grows large sheets of sulfur terminated <0001> planes which are not catalytically active towards thiophene. Wiegenstein and Schulz@footnote 1@ attempted to prepare basal surfaces with large defect densities using deuterium adsorption, but were not successful. Although defects were produced by adsorption of deuterium atoms on sulfur anions which subsequently desorbed as deuterium sulfide, no significant changes were observed in the population of ethyl-thiolate surface species following repeated sample exposures to atomic deuterium. However, reactive MoS@sub 2@(0001) surfaces have been prepared using short ion bombardment times. Three different surface preparation treatments were used: a freshly cleaved surface; a 30 second ion-bombarded surface; and a 60 second ion-bombarded surface. An increase in the population of the higher temperature state was observed as ion-bombardment time was increased. AES results demonstrated that surface sulfur was preferentially removed via ion-bombardment, and thus, the higher temperature state has been identified as arising from methyl-thiolate adsorption at defect sites thought to be sulfur vacancies. This paper will give the details of these studies, and will report on present efforts examining thiophene decomposition on ion-bombarded MoS@sub 2@(0001) surfaces. Finally, the usefulness of the defective basal plane as a model HDS catalyst will be discussed. @FootnoteText@ @footnote 1@Wiegenstein and Schulz, Surface Science, 396 (1998) 284.