Effect of TiO2 Coating on Morphology of Active Phase on Sulfided CoMo/Al2O3 Hydrotreating Catalysts

A series of CoMo catalysts supported on various Al2O3 supports added with TiO2 were prepared to investigate the addition effect of TiO2 on formation of an active phase on sulfided CoMo/Al2O3 catalyst. The catalytic activity tests were carried out with hydrode­sulfurization (HDS) of 4,6-dimethyl­dibenzo­thiophene, hydro­denitrogenation (HDN) of acridine, and hydrode­aromatization (HDA) of o-xylene, 1-methyl­naphthalene (1-MN), and phen­anthrene. A 20 wt % TiO2 added CoMoAlTi20 catalyst showed the lowest hydrogenation activity in HDA of 1-MN and phen­anthrene and highest HDS and HDN activities. The property of a support and/or the interaction between active metal and the support significantly affect the formation of active sites for HDS and HDA. The active sites for HDS on sulfided CoMo catalysts were different from those for HDA and/or hydrogenation. The addition of TiO2 enhanced the reduction, the formation, and stacking number of CoMoS active slabs. The finding that desulfurization via the hydrogenation pathway (HYDS) activity increased while the HDA activity slightly decreased over TiO2 coated catalysts reveals that the increased amounts of formed CoMoS overcome the increase of the stacking number of CoMoS active slabs.