Multidimensional NMR diffusion studies in microporous materials |
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Authors: | Marcel Gratz Markus Wehring Petrik Galvosas Frank Stallmach |
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Affiliation: | aFaculty of Physics and Earth Sciences, University of Leipzig, D-01403 Leipzig, Germany |
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Abstract: | The diffusional behavior of selected hydrocarbons adsorbed in NaX zeolites were investigated with pulsed magnetic field gradient (PFG) NMR methods in two different ways. First, the exchange time τexch of n-pentane between the interior and the exterior of the zeolite crystals was determined by two-dimensional diffusion exchange spectroscopy. The results were compared to the mean life time τintra as obtained by fast NMR tracer desorption method. Second, the diffusion of a propylene–propane mixture adsorbed in the zeolite was studied by Fourier transform PFG NMR, thus employing the chemical shift of the individual organic constituents as a second dimension for a selective evaluation of the PFG NMR signal decays and the subsequent extraction of corresponding diffusion coefficients. Modifications of NMR pulse sequences necessary for the application of ultra-high pulsed magnetic field gradients of up to in microporous materials are briefly discussed for both kind of experiments. |
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Keywords: | 2D NMR Inverse Laplace transformation Fourier transformation Diffusion Exchange NaX |
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