CHARACTERIZATION OF SODIUM-CATIONS IN DEHYDRATED FAUJASITES AND ZEOLITE EMT BY NA-23 DOR, 2D-NUTATION, AND MAS NMR

Sodium cations localized at crystallographically distinct cation sites in dehydrated zeolites were characterized using Na-23 double rotation , two-dimensional nutation, and magic-angle-spinning nuclear magnetic resonance spectroscopy. The new DOR NMR technique has been applied at different magnetic field strengths to determine the quadrupole paramet ers of the overlapping quadrupole patterns. In the NMR spectra of dehy drated NaY and NaEMT two signals of sodium cations were identified, a low-field gaussian line at - 12 +/- 1 ppm and a high-field quadrupole pattern, with an isotropic chemical shift of - 8 +/- 1 ppm and a quadr upole coupling constant of about 4 MHz. By comparison of the Na-23 MAS NMR intensities of these signals with the population of the cation si tes determined by XRD and by calculation of the electric field gradien ts, the former signal was attributed to sodium cations at the sites SI and the latter one to sodium cations at the sites SI' as well as SII in faujasite and zeolite EMT. This assignment has further been confirm ed by Na-23 MAS NMR studies of dehydrated HNaY and BaNaY zeolites.