Preparation of unsupported Ni–Mo–S catalysts for hydrodesulfurization of dibenzothiophene by thermal decomposition of tetramethylammonium thiomolybdates

Unsupported Ni–Mo sulfide catalysts were prepared by thermal decomposition of tetramethylammonium thiomolybdostate and nickel nitrate, which were characterized by Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, thermogravimetric and differential thermal analysis, X-ray diffraction, N2 physorption, elemental mapping and transmission electron microscopy. Hydrodesulfurization of dibenzothiophene was also performed in a fixed-bed reactor over the unsupported Ni–Mo sulfide catalysts. The results showed that the structures and properties of unsupported Ni–Mo sulfides depended on nickel content and decomposition conditions. Ni–Mo sulfides with type IV isotherms related to mesoporous structure were obtained. The layer and stacking degree of sulfide particles showed a decreasing trend, which leaded to a decrease of specific surface area, with increasing nickel content. All elements were homogeneously distributed, suggesting the “Ni–Mo–S” phase was formed. The addition of nickel promoted the dibenzothiophene conversion and the direct desulfurization pathway in the hydrodesulfurization of dibenzothiophene. The sample Ni0.1–MoS2 gave superior hydrodesulfurization activity for dibenzothiophene to other samples. The unsupported Ni–Mo sulfide catalysts exhibited desired activity in hydrodesulfurization and therefore might find wide applications in hydrotreating of fuel oil.