Exploring Mass Transfer in Mesoporous Zeolites by NMR Diffusometry.

Dirk Mehlhorn,Kanghee Cho,Jörg Kärger,Ryong Ryoo,Rustem Valiullin

doi:10.3390/ma5040699

Dirk Mehlhorn, Kanghee Cho + Show 3 more

Open Access

https://doi.org/10.3390/ma5040699

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Abstract

With the advent of mesoporous zeolites, the exploration of their transport properties has become a task of primary importance for the auspicious application of such materials in separation technology and heterogeneous catalysis. After reviewing the potential of the pulsed field gradient method of NMR (PFG NMR) for this purpose in general, in a case study using a specially prepared mesoporous zeolite NaCaA as a host system and propane as a guest molecule, examples of the attainable information are provided.

Highlights

In modern technologies, nanoporous materials find widespread application in shape-selective catalysis and in mass separation by molecular sieving and selective adsorption
The techniques of molecular modeling, which have vividly developed in that time, nicely reproduced the diffusivity data determined by nuclear magnetic resonance (NMR) [22,23,24]—in complete accordance with the underlying assumption that mass transfer occurs under the sole influence of the genuine pore space
The pulsed field gradient method of NMR (PFG NMR) attenuation plots for the mesoporous samples shown in Figures 8 and 9 correspond to those plotted in Figures 4 and 5 for the purely microporous ones

Summary

Introduction

Nanoporous materials find widespread application in shape-selective catalysis and in mass separation by molecular sieving and selective adsorption All these processes are prompted by the intimate contact between the guest molecules and the host surface [1,2,3], which is realized in the best possible way if the pore sizes are close to the molecular dimensions. The techniques of molecular modeling, which have vividly developed in that time, nicely reproduced the diffusivity data determined by NMR [22,23,24]—in complete accordance with the underlying assumption that mass transfer occurs under the sole influence of the genuine pore space. 2012, recognizing the most productive collaboration between his group and the group in Leipzig, in deep appreciation of his contribution to the development in the field and of the eventual break-down of the iron curtain

PFG NMR Diffusion Measurements

The Material under Study

Measurements with the Purely Microporous Samples

Measurements with the Mesoporous Samples

Conclusions