Abstract: Direct functional modification of fluid catalytic cracking (FCC) catalyst additives is a simple and effective method for increasing propylene production. ZSM-5 modified by alkali and different content of phosphorus named XP/A/ZSM-5 was prepared for increasing propylene production in FCC unit,in which x means the loading amount of phosphorus (calculated by the mass fraction of P₂O₅,%) . The structure, acidity and phosphorus forms of modified samples were characterized by XRD, TEM, ³¹P NMR and XPS. The performance of increasing propylene production in FCC process was studied. The results show that the propylene yield of all phosphorus modified samples is better than that of ZSM-5, which is related to the decrease of pore volume and acidity. Among the tested additives, 8.0 P/A/ZSM-5 sample had the best catalytic performance, and the yield of propylene was 8.62%. The interaction mechanism of phosphorus and ZSM-5 zeolites showed that phosphorus could interact with framework aluminum and non-framework aluminum to form AlPO₄ species which were detected on the surface of phosphorus modified zeolites.

Key words: ZSM-5 zeolite, phosphorus modification, catalytic cracking, propylene, interaction mechanism