Hydrodesulfurization of Dibenzothiophene over Ni-Mo-W Sulfide Catalysts Supported on Sol-Gel Al₂O₃-CeO₂

To achieve sulfur content in gas oil at a near-zero level, new catalysts with improved hydrogenation functions are needed. In this work, new Ni-Mo-Mo hydrodesulfurization (HDS) catalysts supported by Al₂O₃-CeO₂ materials were synthesized to evaluate their efficiency in the reaction of HDS with dibenzothiophene (DBT). Al₂O₃-CeO₂ supports different CeO₂ loadings (0, 5, 10 and 15 wt.%) and supported NiMoW catalysts were synthesized by sol-gel and impregnation methods, respectively. The physicochemical properties of the supports and catalysts were determined by a variety of techniques (chemical analysis, XRD, N₂ physisorption, DRS UV-Vis, XPS, and HRTEM). In the DBT HDS reaction carried out in a batch reactor at 320 °C and a H₂ pressure of 5.5 MPa, the sulfide catalysts showed a dramatic increase in activity with increasing CeO₂ content in the support. Nearly complete DBT conversion (97%) and enhanced hydrogenation function (HYD) were achieved on the catalyst with the highest CeO₂ loading. The improved DBT conversion and selectivity towards the hydrogenation products (HYD/DDS ratio = 1.6) of this catalyst were attributed to the combination of the following causes: (i) the positive effect of CeO₂ in forcing the formation of the onion-shaped Mo(W)S₂ layers with a large number of active phases, (ii) the inhibition of the formation of the undesired NiAlO₄ spinel phase, (iii) the appropriate textural properties, (iv) the additional ability for heterolytic dissociation of H₂ on the CeO₂ surfaces, and (v) the increase in Brønsted acidity.