Effect of Ni promoter in the oxide precursors of MoS2/MgO–Al2O3 catalysts tested in dibenzothiophene hydrodesulphurization

NiMoS catalysts supported on MgO–Al2O3 oxides, with 95 and 80 mol% of MgO, were synthesized by sol–gel method. In order to study the Ni promoter effect, MgO–Al2O3 supports were impregnated with a pH = 9 solution of Mo and Ni–Mo, respectively; the catalysts were dried (D) and calcinated (C). Catalytic tests showed a Ni promoter effect of 4.5 on the NiMoMg95Al5-D catalyst and 8.5 on the calcinated one. The latter catalyst is more active than a commercial NiMo/Al2O3 catalyst. On the other side, the catalyst supported on Mg80Al20 solid did not show any Ni promoter effect. Raman and UV–vis diffuse reflectance spectroscopy showed that during the impregnation step, a strong support interaction with the ion MoO42− takes place on the Mo/MgO–Al2O3 solids. After calcination, MoO42− ion remained on the catalyst surface, but increased its interaction with the support. The presence of Ni2+Th, Ni2+Oh and MoO42− ions on dried NiMo/Mg95Al5 catalysts was confirmed, as well as the presence of Ni2+Th, Ni2+Oh, MoO42− and Mo7O246− ions on the calcinated catalyst. This suggests that Ni2+ ion allows polymerization of MoO42− to Mo7O246−, produced by Ni2+Oh–MoO42− and Ni2+Oh–Mo7O246− close interactions. The NiMo/Mg80Al20 solids also showed MoO3 species and a high Ni2+Th concentration. Thus, the Ni promoter effect and therefore, catalytic activity decreased, due to the formation of Ni2+Th–MgO and Ni2+Th–Al2O3 spinels.