Mechanism of Hydrodesulfurization of Dibenzothiophene on Co-Mo/Al2O3 and Co/Al2O3 Catalyst by the Use of Radioisotope 35S Tracer

Abstract In order to estimate the behavior of sulfur on hydrodesulfurization catalyst, the 35 S-labelled dibenzothiophene ( 35 S-DBT) was hydrodesulfurized on sulfided Co-Mo/Al 2 O 3 and Co/Al 2 O 3 in a fixed-bed pressurized flow reactor. During the reaction, the radioactivities of unreacted 35 S-DBT and formed 35 S-H 2 S were monitored. The rate of the release of sulfur on the catalyst was estimated from the rates of an increase and a decrease of the radioactivity in formed 35 S-H 2 S. The activation energies of the release of sulfur were 3.7 and 9.9 kcal/mol for sulfided Co-Mo/Al 2 O 3 and Co/Al 2 O 3 , respectively. The amount of labile sulfur (S 0 ), which could be calculated from the maximum amount of 35 S accommodated on the catalyst, increased with increasing temperature. When it was assumed that sulfur in sulfided Co-Mo/Al 2 O 3 existed in the form of Co 9 S 8 -MoS 2 /Al 2 O 3 , the ratio of labile sulfur to total sulfur did not exceed 50 %, even under conditions where the rate of DBT HDS is relatively high. On the contrary, the ratio of labile sulfur to total sulfur for Co/Al 2 O 3 exceeded 80%.