Study of Hydrodesulfurization of Dibenzothiophene on Ni-Mo/Al2O3, Mo/ Al2O3, and Ni/Al2O3 Catalysts by the Use of Radioisotope 35S Tracer.

Abstract The radioisotope tracer method has been used to quantify the behavior of sulfur on sulfided Ni-Mo/Al 2 O 3 , Mo/Al 2 O 3 , and Ni/Al 2 O 3 . The apparent activation energies of HDS reaction for DBT for the three catalysts were 20 ± 1 kcal/mol. The formation rate constants of 35 S-H 2 S were determined and the amount of labile sulfur on the sulfided catalysts was estimated by tracing the changes in radioactivities of the unreacted 35 S-DBT and the formed 35 S-H 2 S during the HDS reaction of 35 S-labeled dibenzothiophene ( 35 S-DBT). It was deduced that ca. 75% of sulfur in the sulfided Mo/Al 2 O 3 was related to HDS reaction at infinite rate of HDS. Compared with the amounts of labile sulfur in the sulfided Ni-Mo/Al 2 O 3 , Mo/Al 2 O 3 , and Ni/Al 2 O 3 , it was determined that the amounts of labile sulfur were 1.6, 9.8, and 18.4 mg sulfur/g catalyst at 280°C for the three catalysts, respectively. And it was suggested that the sulfur in the form of NiS on the sulfided Ni-Mo/Al 2 O 3 was not labile and that the sulfurs attached to both Mo and Ni atom were more labile and related to HDS. The promotion of Ni for Mo-based catalysts was attributed to the sulfur bonded to both Mo and Ni in the MoS 2 phase being more labile.