Thiophene hydrodesulfurization on MoS2; Theoretical aspects

Hydrodesulfurization (HDS), the removal of sulfur in the form of H2S from petroleum, is a crucial step in the industrial refinement process. Using the extended Hückel tight binding method, we have examined the nature of the active site and the mechanism of desulfurization in the case of thiophene on MoS2. The η5-bound sites, in which the thiophene ring lies parallel to the surface, are particularly advantageous to weakening the SC bond. η1-bound sites are less active. The removal of sorrounding surface sulfurs increases the HDS potential of the η5 geometry, but is ineffective at promoting the poorer adsorption modes. Surface reconstruction has also been examined; the possibility of MoMo pairing is suggested. The effect of poisons and promoters is considered. The role they play in HDS catalysis may be determined by the position they occupy in the MoS2 lattice. Metals which replace a surface molybdenum tend to poison HDS, whereas those which “pseudo-intercalate” between the SS layers can serve to promote the reaction.