Experimental proof of thiophene hydrodesulfurization reaction steps by isotope (14C) labeled thiophene

Hydrodesulfurization of thiophene has been studied over alumina supported sulfided molybdena, nickel-promoted molybdena and over nickel (Mo, NiMo and Ni) catalysts. The experiments were carried out with a mixture of thiophene, labeled with radioactive carbon (thiophene-[G-]-14C) and of non-radioactive tetrahydrothiophene (1:1 mol ratio) in a micro catalytic system. It was established, that the main products were tetrahydrothiophene-14C, 1-butene-14C, 2-butene-14C, butane-14C. Tetrahydrothiophene-14C was a major intermediate in the conversion of thiophene—14C in the experimental condition applied. The amounts of converted tetrahydrothiophene on the catalysts were substantially higher than those of thiophene under the same conditions. Hydrothiophene and dihydrothiophene—14C were intermediate products in the hydrodesulfurization of thiophene and tetrahydrothiophene. The hydrodesulphurization of tetrahydrothiophene was paired with dehydrogenation, producing small amounts of thiophene. The experimental results have been considered in the discussion of the mechanism of thiophene and tetrahydrothiophene desulfurization reaction pathway.