Unsupported cobalt molybdenum sulfide catalysts were prepared from bimetallic CoMo alkyl precursors by in situ activation during the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The bimetallic CoMo precursors were prepared by reaction of tetraalkylammonium thiomolybdate salts, (R4N)(2)MoS4 ( where R = H, methyl, butyl, pentyl or hexyl), with CoCl2 in water at a Co/Mo molar ratio of 0.3. These catalysts exhibit a "Swiss-cheese"-like morphology, high surface areas (from 52 up to 320 m(2)/g), high content of carbon (C/Mo = 2.2-3.3) and type IV adsorption-desorption isotherms of nitrogen. The in situ activation of these tetraalkylammonium thiobimetalate precursors leads to a mesoporous structure with pore size ranging from 2 to 4.5 nm. X-ray diffraction showed that the structure of unsupported cobalt molybdenum sulfide catalysts corresponds to a poorly crystalline structure characteristic of 2H-MoS2 with low-stacked layers. The nature of the alkyl group strongly affects both the surface area and the HDS activity. The catalytic activity is strongly enhanced when using carbon-containing precursors; the CoMo catalysts prepared by in situ activation of Co/[N(C4H9)(4)](2)MoS4 presents the highest HDS activity. The highest surface area of the catalysts was observed for the CoMo catalyst formed from Co/[N(C6H13)(4)N](2)MoS4.