A Mechanistic Study of Thiophene Hydrodesulfurization by the Parahydrogen-Induced Polarization Technique

Thiophenic compounds are the least reactive organosulfur compounds in fossil fuels, and thiophene is widely used as a model substrate in studies of industrially important hydrodesulfurization (HDS) processes. It is generally presumed that the HDS process can proceed by two possible pathways, namely hydrogenation or direct desulfurization. In this work, the parahydrogen-induced polarization technique was successfully utilized in a mechanistic study of a hydrodesulfurization reaction by example of a heterogeneous hydrodesulfurization of thiophene over supported catalysts in the presence of parahydrogen. It was demonstrated that the HDS of thiophene on a MoS2/-Al2O3 catalyst proceeds preferentially by the hydrogenation pathway to form tetrahydrothiophene, followed by desulfurization. In contrast, if a Pt/TiO2 catalyst was used, direct desulfurization to 1,3-butadiene and the hydrogenation pathway both contributed to the overall reaction mechanism.