Hydrodesulfurization with classic Co-MoS₂ and Ni-MoS₂/γ-Al₂O₃ and new Pt-Pd on mesoporous zeolite catalysts

The hydrodesulfurization (HDS) of dibenzothiophene (DBT), tetrahydrodibenzothiophene (THDBT) and hexahydrodibenzothiophene (HHDBT) was studied over Co-MoS₂/γ-Al₂O₃ and Ni-MoS₂/γ-Al₂O₃ catalysts, and the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) over metallic Pt-Pd catalysts supported on mesoporous NaH-ZSM-5. The desulfurization of DBT at 300 °C was faster than that of THDBT and HHDBT, both over Co-MoS₂/γ-Al₂O₃ and Ni-MoS₂/γ-Al₂O₃. Desulfurization of THDBT occurred directly to CHEB and CHB, but desulfurization of HHDBT occurred mainly by dehydrogenation to THDBT and subsequent desulfurization of THDBT. In most cases C-S bond breaking occurred by hydrogenolysis. Pt-Pd/mesoporous NaH-ZSM-5 was much more active than Pt-Pd/γ-Al₂O₃, Pt-Pd/NaH-ZSM-5 and single metal Pt and Pd catalysts in the HDS of 4,6-DMDBT. The much higher rate of the Friedel-Crafts reaction of benzylalcohol with benzene demonstrated that mesoporous NaH-ZSM-5 had accessible mesopores. Noble metals on mesoporous zeolites are very active HDS catalysts and might be considered as catalysts in the second stage of a deep HDS process.