Ni(Co)-Mo-W sulphide unsupported HDS catalysts by ex situ decomposition of alkylthiomolybdotungstates

Ni(Co)-Mo-W sulphide unsupported hydrodesulphurization (HDS) catalysts were prepared by ex situ decomposition of trimetallic (Ni-Mo-W) precursors. The precursors were synthesized by reaction of the tetraalkylammonium thiomolybdotungstates salts, (R4N)4MoWS8 (where R = H, methyl, propyl) with an aqueous solution of Ni(Co)Cl2·6H2O in order to give molar ratios of Ni/[Ni + (Mo + W)] = 0.5 and Co/[Co + (Mo + W)] = 0.3. A new method by the ex situ activation was used. First, the precursors were treated in a stainless steel vessel of 45 mL volume at 523 K for 2 h under argon atmosphere. Subsequently, the respective thiosalt was decomposed under a reductive atmosphere of H2S/H2 (15 vol.% H2S) from room temperature to 673 K, dwell of 2 h at 673 K. All catalysts were tested in the HDS of dibenzothiophene (DBT) and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and BET specific surface area measurements.The ex situ activation method used in this work leads to catalysts with a wide distribution of specific surface areas (from 11.4 to 60.6 m2/g), mesoporous structure with pore size ranging from 18 to 45 Å and type IV adsorption–desorption isotherms of nitrogen, poorly crystalline structures with different morphology and high catalytic activities in the HDS of dibenzothiophene (DBT).