PFG NMR Study of Diffusion in MFI-Type Zeolites:  Evidence of the Existence of Intracrystalline Transport Barriers

Vasenkov, Sergey; Böhlmann, Winfried; Galvosas, Petrik; Geier, Oliver; Liu, and Hui; Kärger, Jörg

doi:10.1021/jp003899f

Cited by 110 publications

(124 citation statements)

References 24 publications

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“…Again the conventional notation of a diffusion coordinate was used to be in accordance with the notations of Eqs. (1), (6) and (10). Using the notation of Fig.…”

Section: Evidence From Intracrystalline Concentration Profilesmentioning

confidence: 99%

A new view of diffusion in nanoporous materials

Kärger

Chmelik

Heinke

et al. 2010

Chemie Ingenieur Technik

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Diffusion is among the rate-controlling processes in the technological application of nanoporous materials, including separation and conversion processes. Over decades, the different techniques of diffusion measurements yielded controversial results. The benefit of novel measuring techniques which, by immediate visual evidence, exemplify the self-consistency of the resulting diffusivities is shown. Furthermore, by quantifying the permeabilities through the particle surfaces and by correlating the rate of molecular uptake and release with the molecular mobilities, these techniques are able to identify and to explore additional transport resistances which so far, though being rate-limiting in numerous cases, were outside the range of direct experimental observation.

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“…Again the conventional notation of a diffusion coordinate was used to be in accordance with the notations of Eqs. (1), (6) and (10). Using the notation of Fig.…”

Section: Evidence From Intracrystalline Concentration Profilesmentioning

confidence: 99%

A new view of diffusion in nanoporous materials

Kärger

Chmelik

Heinke

et al. 2010

Chemie Ingenieur Technik

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“…QENS is the experimental technique which is least affected by the existence of internal barriers. 95,96 As the internal Figure 27. Simulation results for the diffusion of methane in MFItype silica as a function of the adsorbate loading, together with results obtained by several other groups, through simulation [13][14][15][16][17] and experiment.…”

Section: Comparison With Experimental Datamentioning

confidence: 99%

Loading Dependence of the Diffusion Coefficient of Methane in Nanoporous Materials

2006

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In this work, we use molecular simulations to study the loading dependence of the self-and collective diffusion coefficients of methane in various zeolite structures. To arrive at a microscopic interpretation of the loading dependence, we interpret the diffusion behavior in terms of hopping rates over a free-energy barrier. These free-energy barriers are computed directly from a molecular simulation. We show that these free-energy profiles are a convenient starting point to explain a particular loading dependence of the diffusion coefficient. On the basis of these observations, we present a classification of zeolite structures for the diffusion of methane as a function of loading: three-dimensional cagelike structures, one-dimensional channels, and intersecting channels. Structures in each of these classes have their loading dependence of the free-energy profiles in common. An important conclusion of this work is that diffusion in nanoporous materials can never be described by one single effect so that we need to distinguish different loading regimes to describe the diffusion over the entire loading range.

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“…This type of information was, in particular, provided by the pulsed field gradient technique of NMR (PFG NMR) which allows a controlled variation of the observation distance from less than 100 nm up to several tens of μm. [4][5][6] However, in contrast to the situation that prevails during catalytic conversion and separation processes, diffusion measurements by PFG NMR are carried out under equilibrium conditions. This limitation has been overcome by the recent application of micro-imaging to diffusion studies with nanoporous materials, 7,8 notably by the application of interference microscopy (IFM) and IR micro-imaging (IRM).…”

Section: Introductionmentioning

confidence: 99%

Micro-imaging of transient guest profiles in nanoporous host systems of cylindrical symmetry

Binder

Hibbe

Chmelik

et al. 2012

The Journal of Chemical Physics

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Nanoporous host materials giving rise to transient guest profiles of cylindrical symmetry during molecular uptake and release are shown to provide particularly advantageous conditions for the study of guest diffusion by micro-imaging. Considering zeolites of structure type DDR (Deca-dodecasil 3R) as a host system and short-chain length hydrocarbons as guest molecules, the benefits thus attainable in micro-imaging studies using interference microscopy are shown to include the determination of transient concentration profiles with improved accuracy, the option to overcome the disturbing impact of surface imperfections, and easy access to concentration-dependent diffusivities.

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PFG NMR Study of Diffusion in MFI-Type Zeolites: Evidence of the Existence of Intracrystalline Transport Barriers

Cited by 110 publications

References 24 publications

A new view of diffusion in nanoporous materials

A new view of diffusion in nanoporous materials

Loading Dependence of the Diffusion Coefficient of Methane in Nanoporous Materials

Micro-imaging of transient guest profiles in nanoporous host systems of cylindrical symmetry

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