Siliceous framework, oxygen catalyst

Zeolitic catalysts are constituted of [TO4] tetrahedrons which are assembled by sharing oxygens to form one of several topologically distinct framework structures. In the case of alumino-silicates, T=Si with some A1 substitutions, while in silico-alumino-phosphates (SAPO), T sites are occupied by alternating A1 and P atoms with some Si substitutions. The substitutions destroy the electro-neutrality of the framework and necessitate the presence of compensating cations. While mono- or bivalent metallic cations usually occupy crys-tallographically well-characterized sites in the cavities, protons are chemically bonded to framework oxygens. 

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