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

Abstract

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 S_α 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.