Preparation, Characterization Of Supported Ni₂ P Catalysts And Their Hydrodesulfurization Performance Study

Transition metal phosphides(especially nickel phosphide(Ni₂P)) exhibit broad and amazing physical and chemical properties, have recently been reported as a novel catalyst group for deep hydrotreatment and have received much attention because of their high activity for the hydrodesulfurization of fuels. However, the unsupported Ni₂P catalysts have low surface area (<1 m²/g) and low activity, therefore dispersion of the Ni₂P on a high-surface support is needed. TiO₂-Al₂O₃ may form to be a promising support for the hydrodesulfurization of catalysts since it can overcome the disadvantages of low surface of the TiO₂, with the advantages of the high activity of the TiO₂ and the skeletal structures of Al₂O₃.Composite TiO₂-Al₂O₃ supports were prepared by sol-gel method, and supported nickel phosphide catalysts, Ni₂P/TiO₂-Al₂O₃, were prepared by the impregnation method. The catalysts were characterized by X-ray diffraction(XRD), N2-adsorption specific surface area measurements(BET), transmission electron microscope(TEM), standard electronic modules(SEM), Fourier transform infrared spectroscopy(FT-IR), and X-ray photoelectron spectroscopy(XPS). The catalysts were evaluated using a lab-scale continuous flow fixed-bed reactor for the hydrodesulfurization(HDS) of dibenzothiophene(DBT). The effects of the preparation method and calcination temperature of supports, TiO₂ mass fraction, Ni₂P loading, Ni/P molar ratio, calcination temperature of catalyst, reduction temperature, immersion methods and the carrier type were studied. TiO₂ can weaken the strong interaction between Al₂O₃ and Ni₂P, suppress the aggregation of the macro particles and the formation of AlPO₄, and can promote the formation of the active Ni₂P phase. The catalytic activity of the Ni₂P/TiO₂-Al₂O₃ catalyst with a TiO₂ mass fraction of 50%, prepared by the sol-gel method, carrier calcinate at 550℃, Ni₂P loading of 30 wt%, Ni/P molar ratio of 1/1, catalyst calcinate at 500℃, reduction temperature of 700℃, and total immersion method were found to be optimal. At a reaction temperature of 333℃, a pressure of 3.0 MPa, a hydrogen/oil ratio of 500(V/V), a liquid hourly space velocity (WHSV) of 2.0 h^-1 and reaction for 72 h, the HDS conversion of DBT remained stable at 80%. The property of Ni₂P/TiO₂-Al₂O₃ is better than any other catalysts supported by HZSM-5, NaY and USY.