Paramagnetic effect of oxygen in the 23Na MAS NMR and 23Na MQMAS NMR spectroscopy of zeolite LiNaX

The paramagnetic effects of oxygen molecules on the sodium cations in zeolite LiNaX (approximate to 70% Li; 30% Na) were investigated using variable-temperature Na-23 MAS NMR and Na-23 MQMAS NMR. The presence of the oxygen caused a downfield paramagnetic shift for the site III resonance, indicating the accessibility of these cation sites. Although a shift was realized, it is much smaller than what is observed for Li-7 by others. To understand these results, Na-23 MQMAS NMR was used to calculate the isotropic chemical shifts, quadrupolar shifts, and the quadrupolar coupling constants. The quadrupolar coupling constant and quadrupolar shift of the site m sodium remain the same irrespective of the presence or absence of oxygen; however, these values were affected by temperature changes and were found to increase at lower temperatures.