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386 results on '"Ruthven, Douglas M."'

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

Author

Titze, Tobias, Lauerer, Alexander, Heinke, Lars, Chmelik, Christian, Zimmermann, Nils ER, Keil, Frerich J, Ruthven, Douglas M, and Kärger, Jörg

Subjects
Biological Transport, Magnetic Resonance Spectroscopy, Microscopy, Models, Chemical, Nanostructures, Porosity, diffusion, Fick's laws, metal-organic frameworks, nanoporous materials, zeolites, Fick’s laws, Chemical Sciences, Organic Chemistry
Abstract

Diffusion in nanoporous host-guest systems is often considered to be too complicated to comply with such "simple" relationships as Fick's first and second law of diffusion. However, it is shown herein that the microscopic techniques of diffusion measurement, notably the pulsed field gradient (PFG) technique of NMR spectroscopy and microimaging by interference microscopy (IFM) and IR microscopy (IRM), provide direct experimental evidence of the applicability of Fick's laws to such systems. This remains true in many situations, even when the detailed mechanism is complex. The limitations of the diffusion model are also discussed with reference to the extensive literature on this subject.

Published
2015

42. Surface barriers and symmetry of adsorption and desorption processes

Author

Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Economía y Competitividad (España), SASTRE NAVARRO, GERMAN IGNACIO [0000-0003-0496-6331], Sastre, Germán, Kärger, Jörg, Ruthven, Douglas M., Ministerio de Ciencia, Innovación y Universidades (España), Ministerio de Economía y Competitividad (España), SASTRE NAVARRO, GERMAN IGNACIO [0000-0003-0496-6331], Sastre, Germán, Kärger, Jörg, and Ruthven, Douglas M.

Abstract

Adsorption and desorption of hydrocarbons in a realistic model (2496 atoms) of ZSM-5 zeolite (MFI), including an external surface and a reservoir for molecules, have been studied using classical molecular dynamics, with special focus on surface barriers. Different degrees of surface blocking have been modeled according to experimental observations. Using previ-ous molecular dynamics results, from the analysis of adsorption and desorption path lengths, we demonstrate that surface barriers are symmetric, i.e. with equal paths for desorption and adsorption, in agreement with the principle of microscopic reversibility and in contradiction with a model proposed recently. A new thermodynamic analysis confirms the symmetry of adsorption/desorption paths.

Published
2020

47. The diffusion path reversibility confirms symmetry of surface barriers

Author

Sastre, German, Kärger, Jörg, and Ruthven, Douglas M.

Subjects
ddc:530, diffusion, reversibility
Abstract

The resistance perceived by guest molecules upon entering or leaving a microporous host material (the “surface barrier”) is known to often surpass the influence of diffusion in its interior on the overall rate of molecular uptake and release [1, 2]. Our knowledge of the relevant mechanisms of surface permeation, however, is still rather limited. This is related to the difficulties in its direct measurement which, given the “nanoscopic” extension of the relevant space scale, notably exceed the difficulties which do exist with already the diffusion measurement. A question discussed in this context refers to the possibility that the resistance perceived by the molecules on entering the pore space may differ from that perceived upon leaving [3-5].

Published
2019

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