Abstract: Ni-Mo hydrocracking catalysts were prepared by incipient-wetness impregnation method using different proportions of modified Y molecular sieve and amorphous silica-aluminum as acidic components. The catalysts were characterized by N₂ adsorption-desorption, NH₃-temperature programmed desorption, pyridine adsorption infrared spectroscopy, X-ray diffraction and H₂-temperature programmed reduction. The hydrocracking performance of the catalysts was investigated in a fixed-bed reactor with mixed diesel fraction as raw material. The results showed that with the increase of the content of modified Y molecular sieve, the amount of B acid and the ratio of B/L acid in the strong acid range of the catalyst increased first and then decreased. When the content of molecular sieve was too high, the active components were accumulated. At the mass ratio of modified Y molecular sieve to amorphous silica-aluminum of 1.0, the catalyst had moderate specific surface area and pore size, and the active components were well dispersed with the highest amount of B acid in the strong acid range, and the largest ratio of B/L acid. When the catalyst with the mass ratio of Y molecular sieve to amorphous silica-aluminum of 1.0 was used in diesel hydrocracking, the catalyst exhibited the highest activity.So there was the highest conversion efficiency of aromatics in diesel oil, the highest conversion rate of fractions above 250℃, the lowest yield of tail oil and the lowest BMCI.The yield sum of heavy naphtha and jet fuel was the highest, and the aromatic hydrocarbon potential content of heavy naphtha was the highest.

Key words: Y molecular sieve, catalyst, diesel fuel, hydrocracking