Benefit of Microscopic Diffusion Measurement for the Characterization of Nanoporous Materials

Abstract

Detailed knowledge of the transport properties of nanoporous materials is a prerequisite for their complete characterization and optimum technological exploitation. One of the best ways to attain this information is provided by the "microscopic" techniques of diffusion measurement, in particular by the pulsed field gradient technique of NMR and by interference microscopy and IR microscopy. Starting with the measuring principles, the various types of evidence as accessible by these techniques are illustrated. A large variety of host-guest systems with both ordered and random pore networks have been studied, from microporous up to macroporous materials. The information obtained concerns diffusivities in the various pore domains, extra resistances at the interfaces between them and the associated exchange rates.

Mesopore formation in zeolite H-SSZ-13 by desilication with NaOH

“…However, diffusion limitations may also severely restrict reaction rates. During the last decade, attempts have been made to enhance catalyst performance by altering the diffusion properties of the materials [2][3][4][5][6][7][8][9][10][11][12][13][14].…”

A new view of diffusion in nanoporous materials

“…Over the past few years, the understanding of diffusion in nanoporous materials has been notably enhanced by two innovations in the experimental procedure [14]. They include the microscopic observation of the evolution of the guest profiles in the interior of the individual crystallites and the determination of guest self-diffusivities as a function of the externally applied guest pressure.…”

Transport in Nanoporous Materials Including MOFs: The Applicability of Fick’s Laws

“…Examples for which exactly this behavior has been observed include purely microporous and mesoporous zeolites [12] , activated carbon [13] , nanoporous glass [14] and ordered mesoporous silica of type SBA-15. [15] The validity of the Fickian model and the physical meaning of the diffusivity appearing in Eq.…”