by Dieter Freude , Steffen Beckert , Frank Stallmach , Jörg Kärger , Jürgen Haase

1. Ion and water mobility in zeolite Li-LSXstudied by 1H, 6Li and 7Li NMR spectroscopy and diffusometry rotor with sample in the rf coil zr rot  10 kHz B0 = 9  18 T θ Investigation of the water and lithium ion mobility in a crystalline porous material by Dieter Freude, Steffen Beckert, Frank Stallmach, Jörg Kärger, Jürgen Haase Universität LeipzigInstitute fürExperimentellePhysikLinnéstraße5, 04103 Leipzig, Germany The study wasrecently published in Microporous and Mesoporous Materials 172 (2013) 174–181 (15 May 2013). Reprints are available on request nowor by E-mail to freude@uni-leipzig.de. gradient coils forpulsed field gradients, maximum 1 T / m for MAS,but 35 T / m for PFG NMR

2. Pulsed field gradient (PFG) NMR diffusometry B0 5 Spin recovery by Hahn echo without diffusion of nuclei: p p /2 r.f. pulse t gradient pulse t gmax = 25 T / m d free induction Hahn echo y magnetization t D D z z z z B0 B0 B0 y y y y 1 5 4 2 M M 3 3 x x 2 4 1

3. PFG NMR: signal decay by diffusion of the nuclei PFG NMR diffusion measurements baseon radio frequency (rf) pulse sequences. They generate a spin echo, like the Hahn echo (two pulses), orthe stimulated spin echo (three pulses). At right, a sequence for alternatingsine shaped gradient pulses andlongitudinal eddy current delay (LED) consisting of 7 rf pulses, 4 magnetic field gradient pulses of duration , intensity g, observation time , and 2 eddy current quench pulses is presented. The self-diffusion coefficient D of molecules is obtained from the decay of the amplitude S of the FID in dependence on the field gradient intensity g by the equation

4. High-resolution solid-state MAS NMR Fast rotation (1-60 kHz) of the sample about an axis oriented at the angle 54.7° (magic-angle) with respect to the static magnetic field removes all broadening effects with an angular dependency of zr B0 rot θ Chemical shift anisotropy,internuclear dipolar interactions,first-order quadrupole interactions, and inhomogeneities of the magnetic susceptibility are averaged out. It results an enhancement in spectral resolution by line narrowing for solids and for soft matter. The transverse relaxation time is prolonged.

5. MAS PFG NMR  diffusometry with spectral resolution 6 5 4 3 2 d / ppm gradient strength Spectral resolution is necessary for studies of systems consisting of proton species with different mobility. The spectrum shows water molecules which are located in the sodalite cages (signal at 3.8 ppm) having a small mobility and water molecules in the large cavities (signal at 4.9 ppm) having a high mobility in the hydrated zeolite Li-LSX at 373 K (observation time is 100 ms).

6. NMR exchange spectroscopy (EXSY) 1 0 δF2 / ppm 1 0 δF1 / ppm Exchange spectroscopy is a two-dimensional NMR experiment. The free induction signal is monitored as a function of t2. Consecutive experiments give the dependence on t1. After a two-dimensional Fourier transform, we obtain cross peak intensities, which depend on the exchange between the different locations of the nuclei as a function of the mixing time tmix. 2D 6Li MAS NMR exchange spectrum of the zeolite Li-LSX obtained at 373 K with a mixing time of 1000 ms.

7. MAS NMR spectroscopy and MAS PFG NMR diffusometry 1H and 6Li MASNMR spectroscopyand 1H MAS PFG NMR diffusometrywere performed in a wide-bore magnet with the external magnetic field of 17.6 Tesla.

8. PFG NMR diffusometry 7Li PFG NMR measurements were carried out by means of the home-built PFG NMR spectrometer FEGRIS in the external field of 9.4 Tesla. The spectrometer is able to provide pulsed field gradient amplitudes up to gmax = 39.3 Tm-1.

9. Microporous zeolite Li-LSX Watermolecule Faujasite crystallite The lithium form of the low-silica X type zeolite (Li-LSX) has good properties for N2/O2 separation processes, cleaning liquid nuclear waste, CO2 capture from the atmosphere, and hydrogen storage. Li-X zeolites were also used as model systems for the investigation of the electrical properties of nano-scale host/guest compounds. The commercial zeolite Li-LSX consists of crystallites with about 3 µm diameter. A zeolite Li-LSX with a diameter of about 10 µm was used for the present study. Faujasite cage Lithium ion

10. 1H and 6 Li MAS NMR spectroscopyand the results of exchange spectroscopy Signals from species which are locatedin the large cavities and in the sodalite cages 1.0 0.0 -1.0 d / ppm 6.0 5.0 4.0 3.0 2.0 d / ppm 6Li MAS NMR spectrum of the hydrated Li-LSX at373 K 1H MAS NMR spectrum of the hydrated Li-LSX at373 K 2D 1H MAS exchange spectroscopy yields for a 91% lithium exchanged zeolite Li-LSX a value of 40 ms for the mean residence time of a water molecule in the sodalite cage before jumping into the supercage. By 2D 6Li MAS NMR, the mean residence time of a lithium ion on SIc position in the sodalite cage before exchange with a SIIc position is estimated to be 150 ms. The lithium ions on SIIcpositions are in much faster exchange with all cations in the supercage.

11. 1H MAS PFG NMR and 1H PFG NMR Semi logarithmic plot of the decay of the intensity of the 1H MAS PFG NMR (open squares) and 1H PFG NMR (filled squares) signals as a function of the applied gradient strength (-value) for an observation time of 10 ms at a temperature of 373 K. The two-component exponential decay reflects the fast inter-crystalline diffusion and the slower intra-crystalline or intra-particle diffusion. MAS PFG NMR monitors only the less important inter-crystalline effect. The stronger gradients of the PFG NMR are necessary for the observation of the intra-effect.

12. 7Li PFG NMR Semi logarithmic plot of the decay of the intensity of the 7Li PFG NMR signals as a function of the applied gradient strength (-value) for an observation time of 2 ms at a temperature of 373 K (circles), 423 K (triangles) and 473 K (squares) Stronger pulsed field gradients were used for this first 7Li PFG NMR observation of the self-diffusion of cations in zeolites. As usual, the larger crystallites favor the measurement of the intra-crystalline diffusion.

13. Result • Crystallites of zeolite LSX with a diameter of about 10 µm 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 of 1H and 6Li 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 1H and 6Li exchange spectroscopy the mean residence times in the sodalite cages at 373 K are found to be about 40 ms for the water molecules and about 150 ms for the lithium cations. • PFG NMR self-diffusion measurements at 373 K yield a diffusivity of about 2.0 × 10-11 m2s-1 for the lithium ions, whereas the self-diffusion coefficient for the water molecules amounts to D = 2.5 × 10-10 m2s-1. This finding is not trivial, since lithium is strongly hydrated and all water molecules belong to the hydration shells.

14. Conclusions • Crystallites of zeolite LSX with a diameter of about 10 µm 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 of 1H and 6Li 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 1H and 6Li exchange spectroscopy, the mean residence times in the sodalite cages at 373 K are found to be about 40 ms for the water molecules and about 150 ms for the lithium cations. • PFG NMR self-diffusion measurements at 373 K yield a diffusivity of about 2.0 × 10-11 m2s-1 for the lithium ions, whereas the self-diffusion coefficient for the water molecules amounts to D = 2.5 × 10-10 m2s-1. • The cation diffusivity is retarded by about one order of magnitude in comparison with the water diffusivity. This notably exceeds the retardation of cation diffusion in comparison with water in free solution (publication in preparation) , reflecting the particular influence of the zeolite lattice on the guest mobility.