Nickel-Molybdenum-Tungsten Sulfide catalysts prepared by in situ activation of tri-metallic (Ni-Mo-W) alkylthiomolybdotungstates

Abstract

Unsupported nickel–molybdenum-tungsten sulfide catalysts were prepared from tri-metallic Ni-Mo-W alkyl precursors by in situ activation during the hydrodesulphurization (HDS) of dibenzothiophene (DBT). The tri-metallic Ni-Mo-W precursors were prepared by reaction of tetraalkylammonium thiomolibdotungstates salts, (R4N)4MoWS8 (where R=H, methyl, propyl, butyl, cetyl-trimetyl), with NiCl2 in water at a Ni/Mo(W) molar ratio of 2. These precursors are named Ni/(NH4)4MoWS8, Ni/[N(CH3)4]4MoWS8, Ni/[N(C3H7)4]4MoWS8, Ni/[N(C4H9)4]4MoWS8, Ni/[N(C19H42)4]4MoWS8 to give NiMoW-H, NiMoW-C1, NiMoW-C3, NiMoW-C4 and NiMoW-C C catalysts respectively. These catalysts exhibit a “Swiss-cheese”-like morphology, a wide distribution of specific areas (from 6.9–194.07 m2/g) and high content of carbon (C/Mo = 2.5–8.9). The in situ activation of these tetraalkylammonium thiotrimetallates precursors leads to a mesoporous structure with pore size ranging from 10 to 40 A and type IV adsorption–desorption isotherms of nitrogen. X-ray diffraction showed that the structure of unsupported nickel–molybdenum-tungsten sulfide catalysts corresponds to a typical structure of 2H-MoS2 poorly crystalline with low-stacked layers. The nature of the alkyl group strongly affects both the specific area and the HDS activity. The catalytic activity is strongly enhanced when using carbon-containing precursors; the NiMoW catalysts prepared by in situ activation present high HDS activity. The lowest specific area of the catalysts was observed for the NiMoW-H sample.