A family of unsupported NiMoW sulfide catalysts have been prepared by thermal decomposition of mechanically ground tetramethylammonium thiomolybdotungstate and Ni(NO(3))(2) for hydrodesulfurization of dibenzothiophene. The materials were characterized by Fourier transformation infrared spectroscopy. ultraviolet-visible spectroscopy, thermogravimetric analysis, X-ray diffraction, N(2) 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 MoS(2) and/or WS(2) 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 Ni(0.5)MoWS(y) 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 Ni(1.5)MoWS(y) catalyst showed a negative effect due to the formation of nickel sulfides. Ni(0.5)MoWS(y) 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. (C) 2011 Elsevier B.V. All rights reserved.