Comparison between catalytically important zeolites for their catalytic properties and deactivation

The catalytically important low-silica zeolites (viz., HY, CeNaY, CeNaX, and HKL) and highsilica zeolites (viz., HM, H-ZSM-5, H-ZSM-8, and H-ZSM-11) have been compared for their catalytic activity/selectivity in the cracking of cumene and isooctane and isomerization of o-xylene and also for their deactivation due to coke deposition in the cumene cracking. The pentasil zeolites have also been compared for their catalytic activity and shape selectivity in the conversions of methanol and ethanol to aromatics. The involvement of the strong acid sites in the cracking and isomerization reactions on the zeolites has been investigated by selectively poisoning the acid sites with pyridine. The results showed that the zeolites differ widely in their catalytic activity (per active Al and/or strong acid site), selectivity, shape selectivity, and deactivation in the catalytic reactions. The deactivation of the zeolites in cumene cracking was found to occur in the order HM > HKL > HY > CeNaY > CeNaX > H-ZSM-8 > H-ZSM-11 > H-ZSM-5