Abstract:

Unsupported Ni-Mo hydrodesulfurization catalysts were prepared by a coprecipitation method and characterized by X-ray diffraction(XRD), nitrogen physisorption measurement(BET), infrared spectroscopy(Py-IR, FI-IR), H₂-temperaure programmed reduction(H₂-TPR), temperature-programmed desorption of NH₃(NH₃-TPD), Laser Raman spectroscopy(LRS) and gas chromatography analysis(GC-PFPD) tests. The effects of Al₂O₃ and phosphorus addition on the structure of the catalysts were studied. The results indicate that the addition of Al₂O₃ greatly increases the pore diameter, specific surface area, the amount of the L acid sites and also promotes the formation of B acid sites. Addition of phosphorus leads to the formation of the Al-P-O structure instead of the NiAl₂O₄ structure, and weakens the interaction between active phase and Al₂O₃. The amount of tetrahedral Mo species decreases while the anount of octahedral Mo species increases. The catalysts has a longer service life. The catalyst acidity is changed from strong to weak by adding phosphorus. The hydrodesulfurization rate is increased from 94% to 99.8%. At 280 ℃, hydrogen pressure of 4 MPa, liquid hourly space velocity(LHSV) of 1.5 h^-1 and hydrogen-to-oil volume ratio of 500, 4-methyldibenzothiophene, 4,6-dimethyldibenzothiophene and 2,4,6-trimethyldibenzothiophene catalytic cracking are depthly removed in fluid catalytic cracking diesel oil; the sulphur concentration is decreased from 3950 μg/g to 7.9 μg/g.

Key words: unsupported catalysts, Ni-Mo, hydrodesulfurization, aluminium oxide