Two-dimensional triple-quantum 23Na MAS NMR spectroscopy of sodium cations in dehydrated zeolites.

Two-dimensional triple-quantum (2D-3Q) 23Na MAS NMR spectroscopy has been applied for the investigation of sodium cations in dehydrated zeolites NaY, NaEMT, NaZSM-5 and NaMOR. The experiments have shown that the new 2D-3Q technique allows the determination of the isotropic chemical shifts and quadrupolar couplings of sodium cations with SOQE (second-order quadrupolar effect) parameters of up to ca. 4 MHz. In the present work, SOQE parameters of 1.0-1.2 MHz were found for sodium cations located at positions SI in the hexagonal prisms of dehydrated zeolites NaY and NaEMT. The sodium cations located in the 10-ring and 12-ring channels of dehydrated zeolites NaZSM-5 and NaMOR, respectively, are characterized by a SOQE parameter of 2.0 MHz while a value of 3.1 MHz was determined for sodium cations in the sidepockets of the channels in dehydrated NaMOR.