Unsupported NiMoW sulfide catalysts for hydrodesulfurization of dibenzothiophene by thermal decomposition of thiosalts

A family of unsupported NiMoW sulfide catalysts have been prepared by thermal decomposition of mechanically ground tetramethylammonium thiomolybdotungstate and Ni(NO3)2 for hydrodesulfurization of dibenzothiophene. The materials were characterized by Fourier transformation infrared spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric analysis, X-ray diffraction, N2 physorption, scanning electron microscopy, and transmission electron microscopy. The results showed that structures and properties of unsupported NiMoW sulfides depend on nickel content and decomposition condition. XRD revealed a decrease in the stacking along the c direction of the MoS2 and/or WS2 crystalline structures as the nickel content was increased, consistent with a higher dispersion of the metal sulfides observed by electron microscopy. The low nickel content in Ni0.5MoWSy catalyst gave a positive effect on the hydrodesulfurization of dibenzothiophene, as indicated by the greatly increased specific catalytic activity per unit surface area. In contrast, the high nickel content in Ni1.5MoWSy catalyst showed a negative effect due to the formation of nickel sulfides. Ni0.5MoWSy catalyst showed the highest activity in the hydrodesulfurization reaction compared to other samples. The results further suggest that unsupported NiMoW sulfide catalysts may be promising candidates for wide application in hydrotreating of fuel oil.

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► Tetramethylammonium trimetallates were obtained by mechanical grinding route.
► Layer and stacking degree of sulfides showed a decreasing trend with increasing Ni content.
► Low Ni content showed greatly enhanced intrinsic catalytic activity per unit surface area.
► The addition of nickel promoted the hydrogenation pathway in the HDS of DBT.