Thermal stability of high-silica zeolites of the ZSM-5 family

1. The thermal stability of sodium zeolites of the ZSM family differs from one sample to another according to the method of preparation; it increases regularly as the Na content of the crystals is reduced. Such regularity is general for all the samples examined and is independent of the nature of the organic component used in the preparation and of the Si/Al ratio in the crystals. 2. All the ZSM zeolites examined are converted to cristobalite on heating the formation of cristobalite does not seem to result from direct conversion of ZSM-5 → cristobalite; it commences only after the zeolite phase has become wholly, or largely, amorphous.