Effects of surfactants on the sulfurization and hydrogenation activities of Anderson-type Co-Mo heteropolyacid catalysts

CoMo 6 heteropolyacids were modified by cationic surfactants with different alkyl chain lengths to obtain oil-soluble Co–Mo complexes, which were subsequently employed to synthesize highly dispersed hydrodesulfurization catalysts. The surfactants, as structure-directing agents, markedly affected the morphology, specific surface area, and sulfurization degree of the Co-Mo sulfides at the sulfurization stage, resulting in more accessible edge active sites and Brønsted acid sites. Among the various Co-Mo sulfides, the one derived from dodecyl trimethyl ammonium bromide (DTAB)-modified CoMo 6 heteropolyacid (DTA-CoMo-S) exhibited the highest hydrodesulfurization (HDS) reaction rate (1.1×10 −5 mol/(g cat ·s)) for 4,6-dimethylbenzothiophene (4,6-DMDBT) at 330 °C and an initial H 2 pressure of 7.0 MPa. DFT confirmed that H 2 S adsorption and S-O exchange were more likely to occur on the surface of DTA-CoMo 6 during at the sulfurization stage, which was conducive to the sulfurization of the precursor and generated more CoMoS active phases and SO 4 2- groups. These species promoted both the HDS of 4,6-DMDBT and low-temperature cracking reactions of the intermediate products. In addition, the oil-soluble DTA-CoMo 6 complex showed better hydrocracking, HDS and hydrodemetallization performance in the hydrotreatment of vacuum residue.