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

The paramagnetic effects of oxygen molecules on the sodium cations in zeoli te LiNaX (approximate to 70% Li; 30% Na) were investigated using variable-t emperature Na-23 MAS NMR and Na-23 MQMAS NMR. The presence of the oxygen ca used 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 the se results, Na-23 MQMAS NMR was used to calculate the isotropic chemical sh ifts, quadrupolar shifts, and the quadrupolar coupling constants. The quadr upolar 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 l ower temperatures.