Design of the Metal Precursors Molecular Structures in Impregnating Solutions for Preparation of Efficient NiMo/Al2O3 Hydrodesulfurization Catalysts

The molecular structures of metal precursors in the impregnating solution were designed so as to prepare efficient NiMo/Al2O3 hydrodesulfurization (HDS) catalysts. At first, five typical impregnating solutions were designed; the existing metal precursors, such as [Mo-4(citrate)(2)O-11](4-)-like, [P2Mo18O62](6-)-like and [P2Mo5O23](6-)-like species in the solutions were confirmed by laser Raman spectroscopy (LRS). The UV-Vis spectra results indicated that the solutions containing both phosphoric acid and citric acid could change the existing form of nickel species. Five corresponding NiMo/Al2O3 catalysts were prepared by the incipient wetness impregnation method. The LRS analysis results of dried catalysts showed that the above metal precursors could be partly retained on alumina support after impregnation and drying, although the interface reaction between different metal precursors and alumina support unavoidably took place. Then the catalysts were sulfided and characterized by N-2 physisorption, TEM and XPS analyses. The results showed that different metal precursors in impregnating solution could mainly result in the difference in both the morphology of (Ni)MoS2 slabs and the promoting effect of Ni species. The catalyst prepared mainly with [P2Mo5O23](6-)-like species used as precursors exhibited worse dispersion of (Ni) MoS2 slabs and lower ratio of Ni-Mo-S active phases than the one with [Mo-4(citrate)(2)O-11](4-)-like species. Promisingly, the catalyst prepared with co-existing [Mo-4(citrate)(2)O-11](4-)-like, [P2Mo18O62](6-)-like and [P2Mo5O23](6-)-like species showed better hydrodesulfurization activity for 4,6-DMDBT thanks to its more well-dispersed Ni-Mo-S active phases.