Exploring Cation Siting in Zeolites by Solid-State NMR of Quadrupolar Nuclei

Abstract

Solid-state NMR spectroscopy of quadrupolar nuclei(e.g. 7Li, 23Na, 133Cs, 139La) offers considerable potential for determining the location and population of non-framework cation sites in zeolites. However, to obtain reliable results an array of sophisticated NMR techniques has to be applied, e.g. fast magic angle spinning(MAS), double oriented rotation(DOR), two-dimensional nutation, and experiments at different magnetic field strengths. In addition, computer simulation and decomposition of the spectra are prerequisites, and field gradient calculations are very helpful for spectra interpretation. Quantification of the spectra requires careful correction of the experimental line intensities for possible contributions from satellite transitions and/or spinning side bands. The methods for spectra registration and the strategy for line assignments and quantitative evaluation of the spectra are outlined and exemplified by 23Na NMR studies of dehydrated NaY zeolites.