Sodium cation locations in zeolite omega studied by 23Na VASS NMR

Overlapping 23Na NMR signals of zeolite Na-omega are observed by a 2D MAS quadrupolar nutation NMR spectrum and VASS NMR spectra. The low-field Lorentzian shape component centered at − 3 ppm is assigned to the signal of mobile Na+ cations located in twelve-membered ring channels. The high-field component, varying considerably with the spinning angles of VASS NMR spectra, is assigned to the signal of less mobile Na+ cations located in gmelinite cages. The partition between two categories of Na+ cations is determined by the simulation of VASS NMR spectra with the theoretical consideration extended to more general case that both the quadrupolar and chemical shift anisotropic interactions coexist.