Ultra-deep hydrodesulfurization of 4,6-dimethyldibenzothiophene over Mo sulfide catalysts supported on TiO₂-Al₂O₃ composite

Highly dispersed TiO₂ supported on alumina surface were prepared utilizing chemical vapor deposition method. Mo/TiO₂-Al₂O₃ (TiO₂ 10 wt %) was more active in the HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) than Mo/Al₂O₃ and Mo/TiO₂ catalysts under mild operating conditions. The use of TiO₂-Al₂O₃ composites as a support for Mo sulfide catalysts promoted the HDS pathway, whereby the initial hydrogenation of one of the benzene rings adjacent to the S atom reduced the steric hindrance caused by the two methyl groups, thus increasing the 4,6-DMDBT reactivity. XPS investigations of the Mo catalysts before and after sulfidation suggested that the interaction between Mo and Al₂O₃ was stronger than that between Mo and TiO₂-Al₂O₃ composite. The results also suggested a higher reducibility from oxidic to sulfidic Mo species on TiO₂-coated alumina supports. The number of active sites for HDS, known to be the sulfur vacancies that were also called coordinatively unsaturated sites, had probably increased on TiO₂-Al₂O₃ composites.