Synthesis of cocrystallized USY/ZSM-5 zeolites from kaolin and its use as fluid catalytic cracking catalysts
A series of samples of cocrystallized USY/ZSM-5 zeolites were synthesized from kaolin and silica following a sequential two-step procedure with varying content of ZSM-5 (5–25 wt%). The presence of the ZSM-5 phases was confirmed by XRD and 29Si-NMR. The samples were stabilized by steaming and tested as FCC catalysts in the cracking of vacuum gasoil. The results obtained show that effectiveness of ZSM-5 as a propylene booster is enhanced when zeolites USY and ZSM-5 were synthesized in the same kaolin material, instead of using merely the physical mixtures of the two zeolites. This enhancement is attributed to the higher ability of ZSM-5 to crack larger olefins and suppress hydrogen-transfer to the gasoline fraction when the zeolites are grown together.