Simultaneous hydrodenitrogenation and hydrodesulfurization of model compounds on unsupported Ni-Mo-W sulfide catalysts

Unsupported multimetallic sulfides are an outstanding family of hydrotreating catalysts due to their high activity and stability under demanding reaction conditions. Their complexity renders their fundamental study challenging and, therefore, scarce. Thus, the properties needed for obtaining high activity in the removal of sulfur and nitrogen are still unclear. In this work, a series of NiMoW sulfide catalysts were obtained from precursors synthesized by co-precipitation of and decomposition of salt precursors at atmospheric pressure, or hydrothermal conditions. As a result, catalysts with diverse texture and morphology features were obtained and tested in the simultaneous hydrodenitrogenation (HDN) of quinoline and hydrodesulfurization (HDS) of dibenzothiophene (DBT). The HDN of quinoline proceeds rapidly towards hydrogenated bicyclic heteroaromatic compounds, which undergo ring opening and subsequent C-N bond cleavage. The HDN rates were enhanced in the presence of DBT. All sulfide catalysts consist of mixtures of Ni-promoted Mo(W)S₂, and Ni₃S₂. However, different activity rankings are observed, which cannot be correlated with one single catalyst property. Therefore, different combinations of material properties are needed for optimum HDS and HDN rates. That is, high specific surface area and high bulk W content are needed to have high activity, whereas long Mo(W)S₂ slabs have a negative impact.