Ion and water mobility in hydrated Li-LSX zeolite studied by 1H, 6Li and 7Li NMR spectroscopy and diffusometry

Crystallites of zeolite LSX with a diameter of about 10 mu m were synthesized. Crystals of this size are shown to allow the simultaneous investigation of intracrystalline mass transfer phenomena of water molecules and lithium ions in hydrated zeolite Li-LSX by NMR diffusometry. By MAS NMR spectroscopy with the H-1 and Li-6 nuclei, the water molecules and lithium ions are found to yield two signals, a major and a minor one, which may be attributed to locations in the sodalite cages and the supercages, respectively. By H-1 and Li-6 exchange spectroscopy the mean residence times in the sodalite cages at 373 K are found to be about 150 ms for the water molecules and about 40 ms for the lithium cations. PFG NMR self-diffusion measurements at 373 K yield a diffusivity of about 2 x 10(-11) m(2) s(-1) for the lithium ions, which is about one order of magnitude below the water diffusivity. (C) 2013 Elsevier Inc. All rights reserved.