ABSTRACT
Ion-Exchange ............................................................................................. 284 12.3 The Physical Mixture ................................................................................ 286 12.4 Driving Force for the Solid-State Ion-Exchange Process......................... 289
12.4.1 Moisture-Induced SSIE .............................................................. 289 12.4.2 High-Temperature-Induced SSIE ............................................... 290 12.4.3 Reaction-Induced SSIE............................................................... 291
12.5 Conclusions and Recommendations.......................................................... 292 References.............................................................................................................. 292
One of the most important properties of zeolites is their ability to undergo ionexchange. Zeolitic frameworks are inherently anionic by virtue of incorporation of trivalent cations (commonly Al3+) for quadrivalent (commonly Si4+) cations, which are central to the tetrahedral building blocks comprising most zeolites. The anionic framework charge is satisfied by cations, and these cations are often accessible to ion-exchange through the zeolitic pore system. The ability of zeolites to undergo ion-exchange leads directly to their utility in applications such as water softening, but the property also allows chemical modifications to the zeolites, which lead to their utility as catalysts. Protonic forms of zeolites, routinely derived from ionexchange of alkali-metal-containing zeolites, are the most common type of zeolite catalysts, but transition metal and other metal forms are also well known.
