Abstract: Using the modified Y, H-Beta molecular sieves and Y/H-Beta composite molecular sieves as acid components, respectively,the hydrocracking catalysts were prepared by equal volume impregnation method．The catalysts were characterized by XRD, BET, NH₃-TPD, Py-FTIR and H₂-TPR techniques. The results showed that compared with the catalysts prepared by Y molecular sieves and H-Beta molecular sieves, the catalyst prepared by modified Y/H-Beta compound molecular sieve has suitable acid amount and strength, and the active metals are uniformly dispersed, and the cracking and hydrogenation functions of the catalyst are reasonably matched. When the naphthenic straight-run diesel fraction was used as raw material, the composite catalyst could inhibite the secondary cracking obviously at high reaction temperature; and at higher conversion rate, the total liquid yield was the highest and the light naphtha yield was the lowest, while the yield of heavy naphtha was the highest, the potential aromatic of heavy naphtha and the cetane number of diesel fraction were both higher.

Key words: molecular sieve, catalyst, naphthenic straight-run diesel, hydrocracking