Ultra deep hydrodesulfurization of dibenzothiophene derivatives over NiMo/TiO₂-Al₂O₃ catalysts

We have investigated the catalytic activity of NiMo sulfide catalysts supported on TiO₂-coated Al₂O₃ carriers during the HDS of dibenzothiophene, 4-methyldibenzothiophene and 4,6- dimethyldibenzothiophene at 603 K and 3 MPa. TiO₂-Al ₂O₃ supports were prepared by chemical vapor deposition of TiCl₄ on the surface of γ-Al₂O₃ (240 m² g^-1, 0.84 cm³ g^-1). Using XPS, we showed that TiO₂ is highly dispersed on the surface of Al ₂O₃ for TiO₂ loadings up to ca. 14 wt%. Moreover, TiO₂-Al₂O₃ (14 wt% TiO₂) support showed textural properties very similar to those of the parent alumina support. The composite support with TiO₂ loading around 14 wt% was used as support for NiMo sulfide catalysts. The sulfidation degree of Mo, as determined by XPS, was higher for NiMo/TiO₂-Al₂O ₃ than for NiMo/Al₂O₃. This can be attributed to the lower interaction of molybdenum species with the TiO₂-Al ₂O₃ composite support. The hydrodesulfurization (HDS) tests conducted here showed that NiMo/TiO₂-Al₂O ₃ catalysts are more active than NiMo/Al₂O₃ ones for the HDS of dibenzothiophene, 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene. Comparison of product selectivity of cyclohexylbiphenyl (CHB)/biphenyl (BP) values showed that NiMo/TiO ₂-Al₂O₃ catalysts exhibit higher hydrogenation activity than NiMo/Al₂O₃.