NiMo Catalysts Supported on Al-Based Mixed Oxide Prepared By Hydrothermal Method: Effect of Zn/Al Ratio and Addition of Silica on HDS Activity

The effect of Zn/Al ratio and addition of silica to Al–Znx oxides on the structure and catalytic properties of supported NiMo catalysts in hydrodesulfurization reaction of thiophene was studied. NiMo catalysts were synthesized by simultaneous impregnation of Ni acetate and 12-molybdophosphoric acid on Al–Znx and Al–Zn0.16–Si mixed oxide (with x = Zn/Al ratio of 0.05–0.57) prepared by hydrothermal synthesis at 180 °C. Colloidal SiO2 was added to the Al–Znx oxides (Si/Al = 0.3 ratio) to modify textural and structural properties of NiMo catalysts. These materials were characterized by N2 physisorption, SEM, XRD, FTIR, UV–Vis DRS, TPR–H2, TPD–NH3, XPS, HRTEM and tested in thiophene conversion at 280–400 °C and 1.0 MPa. It was found out that the surface area of the supports calcined at 500 °C, decreases with the increasing Zn/Al ratio, which could be due to the interaction of the Zn with the alumina, leading to formation of Zn-spinel. After impregnation of the supports with NiMo active components, the presence of Zn increases the amount of surface Mo in octahedral sites at Zn/Al = 0.21 ratio. At this ratio maximum in HDS activity of NiMo/Al–Znx samples was observed. Addition of silica to Al-Zn mixed oxide (Zn/Al = 0.16) leads to more active NiMo catalyst due to formation of more Ni(Zn)–Mo–S active species as revealed by XRD and HRTEM.