Enhancement of hydrotreating activity of oil-soluble CoMo6 heteropolyacid for 4,6-dimethyldibenzothiophene and vacuum residue by controlling sulfurization degree

An oil-soluble CoMo 6 heteropolyacid was synthesized by modifying the heteropolyacid with a surfactant dioctadecyl dimethyl ammonium chloride, and then was used to prepare highly active sulfided catalyst. The effect of sulfurization degree on the hydrotreating activity of the catalyst was investigated, and the results show that the incompletely sulfurized catalyst exhibited high reactivity for 4,6-dimethylbenzothiophene (4,6-DMDBT) and vacuum residue (VR). The unusual finding was attributed to more CoMoS species and surface oxysulfides, and the latter were probably generated in the partial replacement of O atoms with S atoms during the sulfurization. The acidic oxysulfides (SO 4 2- groups) not only improved the activation of 4,6-DMDBT but also facilitated the cleavage of C-C bonds of the intermediate product 3,3′-dimethylcyclohexylbenzene according to the reaction data and DFT calculation. Besides, the catalysts with incomplete sulfide state exhibited outstanding catalytic performance on the upgrading of VR. The proposed incomplete sulfurization strategy provided a new way to prepare bifunctional hydrogenation catalysts with both desulfurization and cracking activities.