The Role of Cobalt on Hydrodesulfurization and Hydrogenation of Dibenzothiophene and 4,6-Dimethyldibenzothiophene Catalyzed by Co-Mo/Al2O3.

Abstract

Hydrodesulfurization (HDS) of dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) and hydrogenation (HYD) of tetralin were investigated by use of a series of Mo/Al2O3 and Co-Mo/Al2O3 catalysts in the temperature range from 240 to 340°C at 50atm. The activities of DBT and 4, 6-DMDBT for hydrodesulfurization increased with increasing amount of cobalt added at lower Co/Mo molar ratios (below 0.5). At higher Co/Mo molar ratios (above ca. 0.5), however, the promoting effect of cobalt for DBT increased only slightly. Compared with the case of DBT, the promoting effect of cobalt for HDS of 4, 6-DMDBT decreased with increasing Co/Mo molar ratio, the maximum effect was attained when the ratio was 0.5. At the same molar ratio, the rate constants of the formation of biphenyls were approximately 20 times that of unpromoted Mo/Al2O3, while the rate constants of the formation of cyclohexylbenzenes were approximately 4 times. Cobalt enhanced the activity of hydrodesulfurization more than that of hydrogenation. Further, the mode of formation of decalin and cyclohexylbenzenes was nearly the same and it was suggested that hydrogenation of tetralin and DBTs occurred on the same active sites.