Al2O3 and phosphorus effect on the active phase and catalytic performance of Ni–Mo catalysts prepared by coprecipitation in hydrodesulfurization of benzothiophene

Abstract

With the Mo, Ni acting as active constituents and Al2O3, phosphorus acting as additive, Ni-Mo-P-Al unsupported catalyst is synthesized by coprecipitation route. This catalyst is applied in the fluid-bed desulfurization process, with fluid catalytic cracking(FCC) diesel oil serving as the model sulfur compound. The catalysts are characterized by X-ray diffraction (XRD), specific surface area (BET), N2 adsorption and desorption, temperature-programmed desorption of ammonia (NH3-TPD), transmission electron microscopy (TEM), infrared Spectrum (FT-IR), H2 temperature-programmed reduction(H2-TPR), Laser Raman spectroscopy(LRS) and Gas chromatography(GC-PFPD) techniques. It shows that the introduction of Al2O3 contributes a higher surface area and pore volume to the catalysts. With phosphorus addition, the amount of tetrahedral Mo species decreased, and the number of octahedral Mo species increased. The catalyst acidity is changed from strong to weak, and more dispersed MoS2 particles formed with the formation of the Ni–Mo–S phase. At 280 °C, a hydrogen pressure of 4 MPa, an liquid hourly space velocity(LHSV) of 2.0 h−1 and a hydrogen-to-oil ratio of 500, the desulfurization rate reaches 99.8% and the sulfur concentrations decrease from 3950 μg/g to 7.9 μg/g.