Influence of Ni on the active phase and hydrodenitrogenation and hydrodesulfurization activities of MoS₂ catalysts

To obtain type II active phase with higher activity, MoS₂-based catalysts were prepared by thermal decomposition of ammonium tetrathiomolybdate. The influence of Ni adding way and decomposition atmosphere on the microstructures of MoS₂ slabs, chemical state of surface elements, as well as hydrodesulfurization and hydrodenitrogenation activities were investigated. Results indicated that simultaneous impregnation of Mo and Ni precursors caused in situ deposition of amorphous NiMoS₄ over the support surface, which subsequently facilitated the substitution of Mo atoms by Ni atoms at MoS₂ edges. Accordingly, these decorated catalysts exhibited higher dispersion of MoS₂ slabs with more suitable slab length (3–5 nm) and stacking number (2–4), which attributed to larger numbers of rim and corner active sites exposed at the edges. These active sites were essential in hydrogenation and hydrogenolysis reactions. In comparison with N₂ atmosphere, thermal decomposition in H₂ atmosphere was more conducive to the substitution of Mo atoms by Ni atoms at MoS₂ edges, which provided more active Ni-Mo-S structures for the adsorption, activation and hydrogenolysis of quinoline and dibenzothiophene molecules. The catalyst prepared by thermal decomposition of NiMoS₄ in H₂ atmosphere showed superior activities in the quinoline hydrodenitrogenation with 23.8% conversion and in the dibenzothiophene hydrodesulfurization with 93.3% conversion, under the conditions of 340 °C, 3 MPa, a weight hourly space velocity of 23.4 h^–1, H₂/oil volume ratio of 600 and 0.1 g of NMS-H₂ catalysts.