Correlations between wavenumbers of skeletal vibrations, unit-cell size and molar fraction of aluminium of Y zeolites. Removal of non-skeletal Al species with H2Na2EDTA

The unit cell parameter (a0) and wavenumber of the asymmetric internal (ν1) and symmetric external (ν2) stretching vibrations of TO4 tetrahedra and of the double-six ring vibrations (ν3) have been studied for hydrated Na- and NH4-Y zeolites following synthesis and further modification by de-alumination with SiCl4 or by hydrothermal treatment. A set of linear equations were found for dependence of molar fraction of aluminium (α′) determined by chemical analysis and ν1, ν2, a0, respectively, when non-skeletal Al species were extracted with H2Na2EDTA. As the standard deviations Sα of α′ varied from 0.008 to 0.015, the determination of the content of Al in skeleton using i.r. and X.r.d. data is recommended for samples whose ratio Si:Al in the skeleton is below 10. The need for a well defined standard from non-modified zeolite then followed from a comparison of our results with equations already published in the literature. The linear relationship between ν1 and a0 has been found for samples both with and without non-skeletal Al species, which indicates the key importance of skeletal geometric factors to TO4 stretching vibrations.