Biaxial Q-shearing of 27Al 3QMAS NMR spectra: Insight into the structural disorder of framework aluminosilicates

In this contribution, we present the application potentiality of biaxial Q-shearing of Al-27 3QMAS NMR spectra in the analysis of structural defects of aluminium units in aluminosilicates. This study demonstrates that the combination of various shearing transformations of the recorded Al-27 3QMAS NMR spectra enables an under standing of the broadening processes of the correlation signals of disordered framework aluminosilicates, for which a wide distribution of Al-27 MAS NMR chemical shifts and quadrupolar parameters( i.e., second-order quadrupolar splitting and quadrupole-induced chemical shifts) can be expected. By combining the suitably selected shearing transformation procedures, the mechanisms of the formation of local defects in aluminosilicate frameworks, including Al/Si substitution effects in the next-nearest neighbouring T-sites, variations in bond angles, and/or variations in the physicochemical nature of charge-balancing counter-ions, can be identified. The proposed procedure has been extensively tested on a range of model aluminosilicate materials (kyanite, gamma-alumina, metakaolin, analcime, chabazite, natrolite, phillipsite, mordenite, zeolite A, and zeolite Y). (C) 2013 Elsevier Inc. All rights reserved.