Faujasite lattice, isomorphous substitution

Fe with the template ion. DTA studies indicate that Fe-faujasites have lower thermal stability than their Al—analogs.The (OH) vibration frequency shifts from 3540 and 3630 to 3570 and 3643 cm respectively on isomorphous substitution of Al by Fe. Relative changes in the intensity of the ESR peak at g = 4.3 at low temperatures also support the conclusion that iron can be inserted in the fauja-site lattice positions. 

Thomsonlte samples in which Si was replaced by Ge in the zeolite framework. Again in the fifties appeared the remarkable work of Barrer et al. [3] Thomsonite, zeolite A, Faujasite and Harmotome were obtained having gallium and/or germanium in the lattice. These works were followed by a worldwide scientific effort to identify zeolites in which isomorphous substitution could give rise to ... 

The isomorphous substitution of framework aliunimun in faujasite-type zeolites was evidenced by chemical analysis, XRD (unit cell contraction), mid-infra-red spectroscopy (shift of lattice vibrations) and adsorption measurements (hysteresis-free adsorption isotherms) [147] and later by Si MAS NMR spectroscopy [149,150,153] (see Fig. 5). 

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