Resolution improvement of solid-state two-dimensional 23Na nutation NMR spectra by magic angle spinning

Sideband analysis in DOR NMR spectra. II. Real finite inner-rotor speed

DOR (double orientation rotation) solid-state NMR technique is analyzed specifically in the case where numerous (> 4) sidebands are observed on the spectrum. In this case, a rough spectrum analysis leads to the false observation of several impurity species. The total "visible" intensity is smaller than the real one. This may lead to an apparent relative concentration change when several species with very different quadrupole interactions coexist in the sample. Contrary to the MAS technique, the correct analysis of DOR spectra with sidebands very often necessitates the simultaneous introduction of CSA and quadrupole interactions.

Characterization of sodium cations in dehydrated faujasites and zeolite EMT by 23Na DOR, 2D nutation, and MAS NMR

Sodium cations localized at crystallographically distinct cation sites in dehydrated zeolites were characterized using 23Na 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 parameters of the overlapping quadrupole patterns. In the NMR spectra of dehydrated 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 quadrupole coupling constant of about 4 MHz. By comparison of the 23Na MAS NMR intensities of these signals with the population of the cation sites determined by XRD and by calculation of the electric field gradients, 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 confirmed by 23Na MAS NMR studies of dehydrated HNaY and BaNaY zeolites.