Activities of unsupported second transition series metal sulfides for hydrodesulfurization of sterically hindered 4,6-dimethyldibenzothiophene and ofunsubstituted dibenzothiophene

The applicability of transition metal sulfides (TMS) from the second transi tion series in deep hydrodesulfurization (HDS) was examined and compared to that of a traditional, supported CoMo/Al2O3 catalyst. Sulfides of Nb, Mo, Ru, Rh and Pd were studied for HDS of dibenzothiophene (DBT) and 4,6-dimeth yldibenzothiophene (4,6-Me2DBT). Measurements were carried out with unsuppo rted TMS samples at different temperatures and H2S partial pressures. The t rend in DBT HDS activities agreed quite well with those found by previous a uthors. It was furthermore found that the activities of the metal sulfides towards the sterically hindered molecule 4,6-Me2DBT closely followed those for DBT. This is somewhat surprising since the direct sulfur abstraction ro ute was of major importance for DBT while the prehydrogenation route, in wh ich ring-hydrogenation in the DBT skeleton precedes desulfurization, was pr evalent for 4,6-Me2DBT. This suggests that common steps are involved in the two routes. For the unsupported metal sulfides, ring-hydrogenated but not desulfurized DBT and 4,6-Me2DBT products were found in much larger amounts than for supported and promoted MoS2-based catalysts. This can be rationali zed as being due to a relatively higher hydrogenation/desulfurization selec tivity ratio for the different transition metal sulfides. Inhibition by H2S was found to be most pronounced near the center of the transition series.