Effect of Ni promoter in the oxide precursors of MoS 2/MgO–Al 2O 3 catalysts tested in dibenzothiophene hydrodesulphurization

Abstract

NiMoS catalysts supported on MgO–Al 2O 3 oxides, with 95 and 80 mol% of MgO, were synthesized by sol–gel method. In order to study the Ni promoter effect, MgO–Al 2O 3 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/Al 2O 3 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 MoO 4 2− takes place on the Mo/MgO–Al 2O 3 solids. After calcination, MoO 4 2− ion remained on the catalyst surface, but increased its interaction with the support. The presence of Ni 2+ Th, Ni 2+ Oh and MoO 4 2− ions on dried NiMo/Mg95Al5 catalysts was confirmed, as well as the presence of Ni 2+ Th, Ni 2+ Oh, MoO 4 2− and Mo 7O 24 6− ions on the calcinated catalyst. This suggests that Ni 2+ ion allows polymerization of MoO 4 2− to Mo 7O 24 6−, produced by Ni 2+ Oh–MoO 4 2− and Ni 2+ Oh–Mo 7O 24 6− close interactions. The NiMo/Mg80Al20 solids also showed MoO 3 species and a high Ni 2+ Th concentration. Thus, the Ni promoter effect and therefore, catalytic activity decreased, due to the formation of Ni 2+ Th–MgO and Ni 2+ Th–Al 2O 3 spinels.