A High-pressure NMR Tube for PFG Diffusion Studies: Revealing the Specific Confinement in RHO Zeolite

Abstract

Diffusion is ubiquitous in nature and many technological processes, particularly in catalysis and gas separations using nanoporous materials. Interpreting the loading dependence of the self-diffusion coefficient (D_self) of guest molecules in nanopores is imperative to understanding diffusion mechanisms. Pulse gradient field (PFG) NMR is a powerful technique for measuring the D_self of target molecules under various pressures. However, the maximum pressures of commercial NMR tubes (usually<14.0 bar, 1 bar= 101325 Pa) are not high enough to investigate in realistic conditions or a wider pressure range. Herein, we developed a high-pressure tube (HP tube, up to 120 bar) for accurate D_self measurements, particularly in nanoporous material systems, featuring rapid sample loading and recovery. This HP tube bypasses the pressure-resistant design of diameter reduction and is equipped with a suite of sample fill tools, facilitating quick solids loading and non-destructive recovery. Its application to methane diffusion in DNL-6 (RHO) molecular sieve reveals the specifically confined diffusion, highlighting the confinement effect of the d8r structure. The HP NMR tube was confirmed to be a safe and reliable solution for high-pressure diffusion investigation via PFG NMR. This contribution advances molecular transport understanding and enables researchers to optimize materials for energy and catalysis technologies.

Keywords

Diffusion / Porous material / Pulse gradient field (PFG) NMR / High-pressure NMR tube / Confinement effect

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Jilin University, The Editorial Department of Chemical Research in Chinese Universities and Springer-Verlag GmbH

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