Faujasite-Type Structures: Aluminosilicate Framework: Positions of Cations and Molecules: Nomenclature

The framework distorts in response to cations and molecules. Type X zeolite has strong Al,Si long-range order, but the order—disorder in faujasite and Type Y zeolite is equivocal. Positions of framework hydroxyls in heated NH4-exchanged faujasite were inferred from interatomic distances and infrared data. Exchangeable cations in strictly dehydrated specimens occupy sites offering minimum electrostatic energy; the center of the hexagonal prism is preferred. For incomplete dehydration (typical for most commercial catalytic processes), cations bond to residual molecules in the sodalite units. The location of exchangeable cations and water molecules in hydrated specimens is uncertain. Hydration complexes of cations occur in the supercage. In the Al-rich varieties, cations certainly enter the sodalite unit. In the Al-poor varieties, x-ray diffraction evidence on cation positions is equivocal.