On existence of hydroxyl nests in acid dealuminated zeolite Y

• Most reviews of zeolite crystal chemistry present hydroxyl nests as structural entities.
• Mild acid treatment (25 °C) of zeolite NaY was used to create nests.
• TPD revealed no weight loss above 200 °C indicative of the full or partial dehydroxylation of nests.
• FTIR revealed no evidence of hydroxyl nests, but bands indicating the formation of isolated terminal silanol groups appeared.
• Hydroxyl (silanol) nests in zeolites are either transient, existing only below 100 °C or do not exist.

The removal of Al with acid solution from a zeolite framework is customarily associated with formation of framework defects known as hydroxyl nests, but their existence has not been unambiguously confirmed thus far. TPD and FTIR techniques were used here to identify such hydroxyl nests in a 22% acid dealuminated zeolite Y by comparing it to its non-dealuminated parent counterpart. Both zeolites, parent and dealuminated, were analyzed in fully alkaline Cs, Na ion exchanged form. TPD analysis showed that hydroxyl nests cannot be present in samples calcined above 200 °C. FTIR study did not find any evidence for the existence of such units even in hydrated samples which had never been subjected to modification at temperatures higher than 80 °C.

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