Editing Zeolite (section)

===Properties===
[[File:Zeolite structure as an assembly of tetrahedra.png|thumb|458x458px|Microscopic structure of a zeolite ([[mordenite]]) framework, assembled from corner-sharing {{chem|SiO|4}} tetrahedra. Sodium is present as an extra-framework cation (in green). Si atoms can be partially replaced by Al or other tetravalent metals.]]

Zeolites are white solids with ordinary handling properties, like many routine [[aluminosilicate]] minerals, e.g. [[feldspar]]. They have the general formula {{chem2|(MAlO2)(SiO2)_{x}(H2O)_{y}|}} where M<sup>+</sup> is usually H<sup>+</sup> and Na<sup>+</sup>. The Si/Al ratio is variable, which provides a means to tune the properties. Zeolites with a Si/Al ratios higher than about 3 are classified as '''high-silica zeolites''', which tend to be more hydrophobic. The H<sup>+</sup> and Na<sup>+</sup> can be replaced by diverse cations, because zeolites have [[ion exchange]] properties. The nature of the cations influences the porosity of zeolites. 

Zeolites have microporous structures with a typical diameter of 0.3–0.8&nbsp;nm. Like most aluminosilicates, the framework is formed by linking of aluminum and silicon atoms by oxides. This linking leads to a 3-dimensional network of Si-O-Al, Si-O-Si, and Al-O-Al linkages. The aluminum centers are negatively charged, which requires an accompanying cation. These cations are hydrated during the formation of the materials. The hydrated cations interrupt the otherwise dense network of Si-O-Al, Si-O-Si, and Al-O-Al linkage, leading to regular water-filled cavities. Because of the porosity of the zeolite, the water can exit the material through channels. Because of the rigidity of the zeolite framework, the loss of water does not result in collapse of the cavities and channels. This aspect – the ability to generate voids within the solid material – underpins the ability of zeolites to function as catalysts. They possess high physical and chemical stability due to the large covalent bonding contribution. They have excellent hydrophobicity and are suited for adsorption of bulky, hydrophobic molecules such as hydrocarbons. In addition to that, high-silica zeolites are {{Chem|H|+}} exchangeable, unlike natural zeolites, and are used as [[solid acid catalyst]]s. The acidity is strong enough to protonate hydrocarbons and high-silica zeolites are used in acid catalysis processes such as [[fluid catalytic cracking]] in petrochemical industry.<ref>{{Greenwood&Earnshaw2nd}} </ref>
[[File:Zeolite Mordenite (with Al substitution).png|thumb|Zeolite Mordenite with some Si atoms substituted with Al atoms. ]]