On the contribution of the cobalt sulfide phase to the global activity of industrial-type CoMo/Al2O3 catalysts in the HDS of DBT

To analyze if the HDS activity is the result of contributions of both CoMoS and cobalt sulfides phases, a series of CoMo/Al2O3 catalysts with increasing Co/(Co+Mo) ratios (r = 0.1, 0.2, 0.3 and 0.4) prepared by simultaneous impregnation, and composites formed with the CoMo/Al2O3 catalysts and Co/Al2O3, were tested in the hydrodesulfurization of dibenzothiophene. The catalysts were characterized by UV-Visible-NIR and infrared of adsorbed CO spectroscopies. The results showed that the amount of CoMoS adsorbing sites remains basically the same in the series of promoted catalysts, while an increase of the precursor of cobalt sulfide is observed. The activity experiments showed that the addition of Co/Al2O3 to Mo/Al2O3 or CoMo/Al2O3 catalysts promotes both the MoS2 and CoMoS phases, and that the rate constants of CoMo/Al2O3 r = 0.2 and CoMo/Al2O3 r = 0.3 can be closely reproduced with composites of CoMo/Al2O3 r = 0.1 with different amounts of Co/Al2O3, indicating that the increased activity in the series of Co-promoted catalysts is related to the presence of cobalt sulfide. It was evidenced that Co-promoted catalysts are complex systems in which several surface species contribute to the global hydrodesulfurization activity and that cobalt sulfide, far from being a spectator in HDS catalysis, has in fact a secondary but significant role in the global performance of industrial-type CoMo/Al2O3 hydrodesulfurization catalysts. All these contributions must be optimized to obtain highly active and selective hydrodesulfurization catalysts.

Automated summary

The study reveals the significant role of cobalt sulfide in hydrodesulfurization catalysis, emphasizing its importance in achieving highly active catalysts.