The influence of adsorbed molecules on Na-sites in NaY zeolite investigated by triple-quantum 23Na MAS NMR spectroscopy.

The effect of hydration and benzene adsorption on 23Na resonance and the quadrupolar interaction in NaY zeolites is studied by triple-quantum MAS 23Na NMR spectroscopy. In the case of a C6D6/NaY system, the results show that with an increase in benzene loading, there is an up-field trend in isotropic chemical shift (delta CS) and a decreasing second order quadrupolar effect (chi s) for the site II sodium ions. It was found that adsorbed benzene molecules have a slight effect on the environment of sodium ions on site I. All the sodium sites in NaY are influenced upon hydration. The up-field shift of the sodium delta CS reflects the effect of coordination of oxygen atoms on sodium cations due to hydration. The magnitude of chi s for hydrated sodium sites increases and then falls off with water loading. The increase in chi s is due to the initial hydration among SI-, SI'- and SII-sodium ions, while the decrease is the result of approaching the final stage of saturated hydration.