Unsupported CoMoW sulfide hydrodesulfurization (HDS) catalysts were prepared by in situ decomposition of sulfur-containing precursors. The precursors were synthesized by reaction of the ammonium and tetraalkylammonium thiomolybdotungstates (R4N)(4)MoWS8 (where R = H, methyl, propyl) with an aqueous solution of CoCl2 center dot 6H(2)O in order to give molar ratios of Co/[Co + (Mo + W)] = 0.3. Co-promoted precursors were then in situ decomposed during the HDS of dibenzothiophene (DBT)-producing CoMoW sulfide catalysts. Solids were analyzed after the in situ activation by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction and for textural properties by using the BET and BJH methods. Catalysts with relatively high surface area and type IV N-2 adsorption-desorption isotherms were obtained. The use of the Co-promoted ammonium thiomolybdotungstate as precursor was found to be beneficial in the catalytic activity. The positive role of carbon in monometallic HDS catalysts confirmed by Chianelli and Berhault was not evidenced here since the catalytic activity decreased with the introduction of an alkyl group in the precursor. (C) 2014 Elsevier B.V. All rights reserved.