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-Al2O3 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 Al2O3 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-Al2O3 than for NiMo/Al2O3. This can be attributed to the lower interaction of molybdenum species with the TiO2-Al2O3 composite support. The hydrodesulfurization (HDS) tests conducted here showed that NiMo/TiO2-Al2O3 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/TiO2-Al2O3 catalysts exhibit higher hydrogenation activity than NiMo/Al2O3.