Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 51: Surface chemical reactions I

O 51.4: Vortrag

Donnerstag, 26. März 2009, 17:00–17:15, SCH A01

Theoretical cluster studies on the catalytic sulfidation of MoO₃ — •Xuerong Shi^1,2, Jianguo Wang², and Klaus Hermann¹ — ¹Theory Department, Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin and Sfb 546 "Transition Metal Oxide Aggregates", Berlin (Germany). — ²State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, Shanxi 030001, P. R. China

Sulfidation of molybdenum trioxide, MoO₃, yielding local surface regions of molybdenum disulfide, MoS₂, is an essential step to improve the hydrotreating activity of Mo catalysts. Therefore, theoretical studies of sulfided MoO₃ surfaces can contribute to an understanding of detailed reaction mechanisms at corresponding catalyst surfaces. We apply density functional theory together with large cluster models to obtain information about the behavior of oxygen and sulfur adsorbates at local sections of the MoO₃(010) surface with and without oxygen vacancies. In all cases, adsorbed oxygen is found to bind more strongly with the substrate than sulfur with binding distances that are shorter than those for the sulfur adsorbate. S/O exchange reactions at the substrate surface are always energetically preferred over sulfur adsorption. In addition, the first and second sulfur substitution takes place preferentially at the singly coordinated oxygen site O(1). Finally, the calculations show that pre-adsorbed hydrogen can facilitate the sulfidation process at the MoO₃(010) surface.