CoNiMo/Al2O3 sulfide catalysts for dibenzothiophene hydrodesulfurization: Effect of the addition of small amounts of nickel

Trimetallic CoNiMo hydrodesulfurization (HDS) catalysts were herein synthesized on Al2O3 support through an incipient wetness co-impregnation procedure using ammonium heptamolybdate and cobalt (and nickel) acetate as precursors. CoNiMo catalysts were obtained by adding in a small proportion of nickel with a molar amount representing between 1 and 10% of the total Co atomic loading. This addition of low amounts of nickel allows keeping the (Co + Ni)/(Co + Ni + Mo) molar ratio close to the optimum value of 0.3. The as-formed catalysts were labeled as CoNixMo/Al2O3 with x the relative stoichiometry of Ni compared to Co. Catalysts were then characterized by N-2 adsorption-desorption isotherms, X-ray diffraction, ICP-OES spectroscopy, Raman spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Catalysts were tested in the HDS of dibenzothiophene (DBT). Results show a significant impact of adding small amounts of nickel to alumina-supported Co-promoted MoS2 on the final HDS activity. While up to CoNi0.03 Mo/Al2O3, the resulting HDS activity is hardly influenced by the addition of nickel, a strong beneficial effect is observed for CoNi0.05Mo/Al2O3 with activity reaching a value of 7.2 x 10(-7) mol.g(cat)(-1).s(-1). Increasing further, the amount of nickel abruptly decreased the DBT HDS activity. Interpretation of these results is then provided considering the additional role of nickel for improving the intrinsic activity of the HDS sites.