High‐field nuclear magnetic resonance of thallium in zeolites

Abstract

Thallium-205 NMR is reported for several zeolite samples (A, X and Y; hydrated and dehydrated) with thallium(1) exchanged for sodium. Detection at high field (7.05 T) clarifies the spectrum appearance, and it is seen that chemical shift anisotropy (CSA) dominates some of the band shapes. The large CSAs dictate that the spectrum is recorded piecewise by a frequency-stepped s p i e c h o integral (FUSSI) method. Magic-angle sample spinning has been observed to give only a very minor line-narrowing effect. Threefold-coordinated zeolite A TI+ sites adjacent to six-membered rings ITI(1) and TI(3)l are both assigned to a resonance which has large CSA (aiso 1183, A6 -1842), while the remaining zeolite A site ITI(2)l gives an isotropic line shape (aLso 300). Dehydrated zeolite X gives an isotropic peak 854) which is assigned to the douhle six-ring TI(I), and a broader anisotropic resonance which is tentatively attributed to supercage TI(I1I). Data for dehydrated zeolite Y indicate that this has a disordered cation distribution.