The influence of cation exchange on the ²⁷Al-NMR spectra of NaA-zeolites has been
studied by ²⁷Al-MAS- and MQ-MAS-Solid State-NMR. From the ²⁷Al-spectra a characterization of the different Al sites in the A zeolites according to their chemical
environment and the structural changes on the aluminosilicate network caused by the
cation exchange are obtained. It is found that the exchange with cations with smaller
ion-radius cause stronger distortions of the ²⁷Al-NMR-spectra than exchange with larger
cations like Ba²⁺. Employing MQ-MAS spectroscopy these distortions are revealed as
second order quadrupolar effects for the smaller cations and as a combination of chemical
shift and second order quadrupolar interaction for the Ba cation. These changes of the
quadrupolar coupling are interpreted numerically via calculations of the lowering of the
symmetry of the EFG tensor. Finally it is found that the exchange with divalent cations
leads to distortions of the zeolitic framework and the formation of an extra-framework
aluminum. To the best of our knowledge this is for the first time that evidence for the
production of extra frame work aluminum by pure cation exchange without any thermal
treatment has been found in type A zeolites