ABSTRACT
Zeolites are microporous crystalline aluminosilicates, composed of TO4 tetrahedra (T=Si, Al) with O atoms connecting neighboring tetrahedra. For a completely siliceous structure, combination of TO4 (T=Si) units in this fashion leads to silica (SiO2), which is an uncharged solid. Upon incorporation of Al into the silica framework, the +3 charge on the Al makes the framework negatively charged, and requires the presence of extraframework cations (inorganic and organic cations can satisfy this requirement) within the structure to keep the overall framework neutral. The zeolite composition can be best described as having three components:
The extraframework cations are ion exchangeable and give rise to the rich ion-exchange chemistry of these materials. The novelty of zeolites stems from their microporosity and is a result of the topology of the framework.
