Hydrodesulfurization of thiophenic compounds: The reaction mechanism

Abstract

It has often been assumed that catalytic hydrodesulfurization of thiophenè and related compounds proceeds via a one-point “end-on” adsorption involving bonding of the sulfur atom with Mo ions at an anion vacancy on the catalyst surface. This interpretation is inadequate, failing to account for hydrogen-deuterium exchange results, the reactivities of benzothiophene and dibenzothiophene, and the small steric effects of methyl substituents on the adsorption and reaction of compounds in the thiophene, benzothiophene, and dibenzothiophene families of homologs. An alternative mechanism, presented here, involves a multipoint adsorption of the reactant, with a CC bond interacting with a Mo cation, and the S atom of the reactant interacting with a S ion on the surface. The new mechanism accounts for the observed deuterium exchange and hydrodesulfurization reactions and is consistent with the observed steric effects.