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 Å 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.