Abstract
Porotektosilicate frameworks of zeolites, including high silica materials, are considerably more reactive than we tend to think. This has been demonstrated by studies of /sup 18/O exchange between high-purity samples of sysnthetic zeolite ZSM-5 in the ammonium form and liquid water at 95/sup 0/C. The investigation of the /sup 18/O-exchange kinetics revealed a two-step reaction which can be interpreted in terms of hydroxyl groups exchanging relatively rapidly (primary exchange) and oxygen atoms from T-O-T bridges exchanging at a rate about 40 times slower (secondary exchange). Since the T sites in ZSM-5 contain mostly Si and only minor amounts of Al, the reported findings imply that not only Si-O-Al but also Si-O-Si bridges are cleaved under relatively mild conditions in the presence of water. 2 figures, 1 table.
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