(41e) Unsupported NiMoW Sulfide Catalysts Prepared by Thermal Decomposition of Thiosalts for Hydrodesulfurization of Dibenzothiophene

More and more stringent environmental regulations and fuel specifications are demanding a significant reduction of sulfur and nitrogen containing compounds, as well as aromatics in fuels. Conventional hydrotreating processes are performed over alumina supported sulfide catalysts based on Mo or W and promoted with Ni or Co. These materials are produced by sulfidation of the corresponding oxides. It well known that incomplete sulfidation due to strong interaction between metal and support results in decreased hydrotreating activity [1]. Unsupported sulfide catalysts have attracted recent attention due to their high activity in the hydroteating reactions. The structures and catalytic properties of these sulfides obtained by comaceration [2], precipitation [3], and hydro/solvothermal route [4] depended strongly on their preparation atmosphere and thermal treatment conditions. Thiosalt decomposition provides a simple and reproducible method for obtaining unsupported sulfide materials with controlled stoichiometry and specific surface area [5]. Herein, a family of unsupported NiMoW sulfides with different ratios were prepared by thermal decomposition of tetramethylammonium thiomolybdotungstate and Ni(NO₃)₂. The catalytic 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 show that structures and properties of unsupported NiMoW sulfides depend on nickel content and decomposition condition. The layering and stacking degree of the sulfide particles shows a decreasing trend as the nickel content increases in the NiMoW sulfides. This family of catalysts was evaluated for the hydrodesulfurization (HDS) of dibenzothiophene (DBT). Low nickel content NiMoW catalysts gave a positive effect on the HDS performance, while catalysts with high nickel content showed a negative effect. The Ni_0.5MoWS_x catalyst showed the highest activity in the HDS reaction compared to other samples. The results suggest that unsupported NiMoW sulfide catalysts may be promising candidates for wide application in hydrotreating of fuel oil. 

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