Special Issue "Diffusion in Micropores"

Guest Editor
Prof. Dr. Sergey Vasenkov
Department of Chemical Engineering, University of Florida, 423 ChE Bldg., PO Box 116005, Gainesville, FL 32611, USA
Website: http://www.che.ufl.edu/faculty/vasenkov/
E-Mail:
Phone: +1 352 392 0315
Fax: +1 352 392 9513
Interests: transport in porous materials with hierarchy of pore sizes; dynamics in room temperature ionic liquids; single-file diffusion in nanochannels; separations of greenhouse gases

Guest Editor
Dr. Siegfried Fritzsche
Department of Molecular Dynamics/Computer Simulation, Faculty of Physics and Geosciences, Institute for Theoretical Physics (ITP),University of Leipzig, Postfach 100920, 04009 Leipzig, Germany
E-Mail:
Interests: molecular dynamics computer simulations (MD); diffusion in porous materials; transport processes; surface effects; zeolites; metal - organic frameworks (MOF)

Dear Colleagues,

Last decade is characterised by the most remarkable progress in the introduction and further development of advanced microporous materials such as metal-organic framework materials (MOFs), single wall carbon nanotubes, and zeolites. These materials are important for many applications including catalysis, separations, molecular storage and sensor development. The majority of these applications involves transport of molecules and ions in micropore networks of these matarials. Hence, detailed fundamental understanding of transport properties of guest species in micropores is crucial for both applied and basic research related to microporous solids. Recent studies of sorbate diffusion in microporous materials resulted in fascinating discoveries related to normal diffusion, and also anomalous diffusion, such as single-file diffusion in micropores. These discoveries become possible due to most recent development of many new experimental techniques allowing monitoring molecular transport on various length scales of displacements under different experimental conditions and by the further development and application of multiscale computer simulations.

Dr. Siegfried Fritzsche
Prof. Dr. Sergey Vasenkov
Guest Editors

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• advanced membranes
• hybrid materials
• anomalous transport
• surface diffusion
• pore diffusion
• channel diffusion
• sorption properties

Type of Paper: Review
Title: Sorbate Transport in Carbon Molecular Sieve Membranes and FAU/EMT Intergrowth by Diffusion NMR
Authors: Robert Mueller ¹, Rohit Kanungo ¹, Amrish Menjoge ¹, Mayumi Kiyono-Shimobe ², William J Koros ², Steven A. Bradley ³, Douglas B Galloway ³, John J. Low ³, Sesh Prabhakar ³ and Sergey Vasenkov ¹
Affiliations: ¹ Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA; E-Mail: svasenkov@che.ufl.edu
² School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
³ UOP LLC, A Honeywell Company, 25 E. Algonquin Road, Des Plaines, Il 60017-5017, USA
Abstract: In this paper we present and discuss selected results of our recent studies of sorbate self-diffusion in microporous materials.  The main focus is given to transport properties of carbon molecular sieve (CMS) membranes as well as of the intergrowth of FAU-type and EMT-type zeolites. CMS membranes show promise for applications in separations of mixtures of small gas molecules, while FAU/EMT intergrowth can be used as an active and selective cracking catalyst. For both types of applications diffusion of guest molecules in the micropore networks of these materials is expected to play an important role. Diffusion studies were performed by a pulsed field gradient (PFG) NMR technique that combines advantages of high field (17.6 T) NMR and high magnetic field gradients (up to 30 T/m). This technique has been recently introduced at the University of Florida in collaboration with the National Magnet Lab. In addition to a more conventional proton PFG NMR, also carbon-13 PFG NMR was used.
Keywords: carbon molecular sieve; zeolite; FAU/EMT intergrowth; diffusion; NMR

Title: Simulating Microwave-Driven Diffusion in Anisotropic Zeolites
Authors: Julian E. Santander ¹, W. Curtis Conner, Jr. ², Hervé Jobic ³, and Scott M. Auerbach ^1,2
Affiliation: ¹ Department of Chemistry, University of Massachusetts, Amherst, MA 01003, USA; E-Mail: auerbach@chem.umass.edu
² Department of Chemical Engineering, University of Massachusetts, Amherst, MA 01003, USA
³ Institut de Recherches sur la Catalyse, Ecole Normale Superiore de Lyon, France
Abstract: We studied the effects of microwave (MW) heating on diffusion of methanol along silicalite, a spatially anisotropic zeolite framework.  We computed the conventionally heated and MW heated diffusion coefficients for this host-guest system.  We benchmarked the effects of framework anisotropy by comparing to diffusion of methanol in all-silica FAU zeolite.  We modeled single-crystal MW-driven diffusion experiments wherein the direction of the MW field can be controlled, changed from along the Z-axis to the X- and Y-axes.  We found that for low temperatures, methanol diffusion in silicalite takes place almost entirely along the (a-axis) zigzag channels, and upon heating conventionally above 500 K we observe diffusion in the straight channels.  This phenomenon was quite different in the MW heated systems.  In this case, the MW selectively heats the methanol molecules, and even though the average system temperature was below 500 K, methanol's translational temperature was well above, allowing diffusion to equally take place through the zigzag and straight channels.  Finally, we found that the MW field orientation has no substantial influence on either methanol heating or diffusion.