Hydrodesulfurization of 4,6-dimethyldibenzothiophene and dibenzothiophene over alumina-supported Pt, Pd, and Pt-Pd catalysts

The activity and selectivity of alumina-supported Pt, Pd, and Pt-Pd in the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DM-DBT) were investigated, and all final, hydrocarbon products and partially hydrogenated intermediates were analyzed. Pd had a high activity in the hydrogenation of 4,6-DM-DBT, whereas the removal of sulfur from DBT and 4,6-DM-DBT and their intermediates occurred faster over Pt than over Pd. Bimetallic Pt-Pd catalysts were much more active than the combination of their monometallic constituents, proving a chemical synergism between the noble metals and the presence of alloyed particles. New sites with high hydrogenation activity explain why the hydrogenation of the products 3,3′3,3′-dimethylcyclohexylbenzyl and 3,3′3,3′-dimethylbiphenyl in the HDS of 4,6-DM-DBT, as well as the hydrogenation of 3,3′3,3′-dimethylbiphenyl in the presence of DBT, were significant only over the Pt-Pd catalysts. In contrast to the metal sulfide catalysts, the hydrogenation route over the noble metal catalysts was faster for 4,6-DM-DBT than for DBT, which almost compensated for the loss of activity via the desulfurization pathway.