Topological changes in dehydrated zeolites: breaking of T-O-T oxygen bridges

Some zeolites show heat-induced phases stable over a long period of time. This stability is a consequence of the breaking of T-O-T bridges, causing topological changesin the framework. Some zeolites whose framework are chacterized by the presence of 6R or 4-4-1 Secondary Building Units exhibit a thermal behaviour of this type. In some cases the framework of the heat-indiced pahse is topologically that of a known mineral, in others it differs from that of any know mineral. Topological changes are explained by the extraframework cation movement causing a strain on the T-O-T bridges. This favours proton attack and the consequent breaking of these bonds. The process can occur only when water is present.