Application of the thermal frequency response method and of pulsed field gradient NMR to study water diffusion in zeolite NaX

Abstract

The thermal frequency response and pulsed field gradient NMR methods are applied in a comparative study of water diffusion in zeolite NaX under non-equilibrium and equilibrium conditions. The obtained results are found to be in satisfactory agreement with each other, indicating that by applying the thermal frequency response method, complications due to uncontrolled water adsorption at the chamber walls inherent in conventional frequency response measurements may be circumvented.

Mass Transfer in Micro- and Mesoporous Materials

“…Differences in molecular positions at two subsequent intervals, however, represent nothing other than their displacements. As an analytical expression of the attenuation of the NMR signal one obtains [6,9,27], Macroscopic Sorption/Desorption [10] Frequency Response (FR) [11] Zero Length Column (ZLC) [12] IR-FR [13] Positron Emission Prof. (PEP) [14] Temporal Product Analysis (TAP) [15] IR Spectroscopy [16] MembranePermeation [5] Effectiveness Factor during Catalytic Reaction [17] Tracer Sorption/Desorption [6] Tracer ZLC [12] Mesoscopic IR Microscopy [18] Single-Crystal Permeation [19] Tracer IR Microscopy [18] Microscopic Interference Microscopy [20] Pulsed Field Gradient NMR (PFG NMR) [1,6] Stray Field Gradient NMR (SFG NMR) [21] Quasi-Elastic Neutron-Scattering (QENS) [22] Exchange NMR [23] where d, g and t denote the width, amplitude and separation of the gradient pulses. The ªgyromagnetic ratioº c is a characteristic quantity of the given nucleus.…”

Diffusion Measurements by NMR Techniques

“…Once equilibrium is established, the measurements may be repeated as often as desired. There are examples [162], where more than 20 years after the first measurement, PFG NMR measurement of an adsorbate-adsorbent system within a closed sample tube yielded identical diffusivities.…”

“…Transport diffusion may be measured under both steady-state conditions (e.g., by studying the permeation rates through zeolite membranes J. Kärger 189]) and transient conditions, as for example, by measuring the rate of molecular adsorption or desorption, in the frequency response technique [162,[190][191][192][193] or in chromatographic measurements [194,195]. Among the chromatographic techniques, the zero length column (ZLC) method [186,[196][197][198] has attained particular relevance since it allows the observation of transport diffusion and-by applying isotopes-of self-diffusion with rather fast response times [199].…”

Stofftransport in mikro- und mesoporösen Materialien

“…Gl. Diese Aufgabe wird durch die unterschiedliche Spezifikation der Messverfahren, wie sie in Tab [11] Zero Length Column (ZLC) [12] IR-FR [13] Positron Emission Prof. (PEP) [14] Temporale Produkt-Analyse (TAP) [15] IR-Spektroskopie [16] Membran-Permeation [5] Porennutzungsgrad bei chem. Die erste Anwendung eines mikroskopischen Verfahrens, nämlich der PFG NMR, auf die Untersuchung der zeolithischen Diffusion lieferte Diffusionskoeffizienten, die bis zu fünf Gröûenordnungen über den bis dahin anerkannten Werten lagen [6 ± 8, 24 ± 27].…”

“…gilt in erster Näherung auch dann noch, wenn der Propagator von Gl (8). B 13. PFG NMR-Untersuchungen an porö-sen Systemen sind aber auch mit anderen Kernen wie z.…”