Effects of Ni–Al2O3 interaction on NiMo/Al2O3 hydrodesulfurization catalysts

A series of NiMo/γ-Al2O3 hydrodesulfurization (HDS) catalysts with different metal–support interactions were first prepared by a conventional impregnation method through changing the calcination temperature. The physicochemical properties of nickel species and molybdenum species in the oxidic and sulfidic catalysts were characterized by X-ray fluorescence spectroscopy, X-ray diffraction, N2 adsorption–desorption, ultraviolet–visible spectroscopy, Raman spectroscopy, H2 temperature-programmed reduction, X-ray photoelectron spectroscopy, and high resolution transmission electron microscopy. It was found both the interaction between nickel and γ-alumina (Ni–Al2O3 interaction) and the interaction between molybdenum and γ-alumina (Mo–Al2O3 interaction) gradually increase with increasing calcination temperature. However, the calcination temperature has a weak influence in the sulfidation degree of molybdenum species but a huge effect on the decoration degree of Ni species on edges of MoS2 nanoslabs. The decoration degree of Ni species visibly declines with increasing calcination temperature, but the sulfidation degree of molybdenum stays nearly parallel at the same time, indicating that Ni rather than Mo is more sensitive to the calcination temperature. In addition, the MoS2 morphology could be impacted by the availability of surface nickel atoms. These results suggest that the Ni–Al2O3 interaction imposes a more dominant influence on the HDS catalysts. Then the HDS performance was evaluated using dibenzothiophene as the model reactant, and through correlating the catalyst structures with the activity, an original suggestion about the effects of the Ni–-Al2O3 interaction on HDS performance was given: the Ni–Al2O3 interaction not only enhances the availability of surface nickel atoms to form more Ni–Mo–S active sites, but also improves the microstructures of MoS2, i.e., shorter nanoslabs and higher stacking layers, which together enhance the apparent activity and intrinsic activity of Ni–Mo catalysts. The present work reveals that finely adjusting Ni–Al2O3 interaction is an effective strategy for improving the performance of hydrodesulfurization catalysts.