Guest-specific diffusion anisotropy in nanoporous materials: Molecular dynamics and dynamic Monte Carlo simulations |
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Authors: | P Bräuer A Brzank L A Clark R Q Snurr J Kärger |
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Institution: | 1. Universit?t Leipzig, Fakult?t für Physik und Geowissenschaften, D-04103, Leipzig, Germany 2. Department of Chemical & Biological Engineering, Northwestern University, Evanston, IL, 60208, USA
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Abstract: | For anisotropic nanoporous materials, guest diffusion is often reflected by a diffusion tensor rather than a scalar diffusion
coefficient. Moreover, the resulting diffusion anisotropy may notably differ for different guest molecules. As a particular
class of such systems, we consider an array of two types of channels, mutually intersecting each other, where the rates of
diffusion in the different directions depend on the nature of the guest molecules. The simultaneous adsorption of two types
of guest molecules is considered, as in technical applications of porous materials such as catalysis. A case study is presented
in which atomistic molecular dynamics (MD) and coarse-grained dynamic Monte Carlo (DMC) simulations are compared and shown
to yield qualitatively similar results for non-steady-state diffusion. The two techniques are complementary. MD simulations
are able to predict the details of molecular propagation over distances of a few unit cells, whereas the evolution of sorption
profiles over distances comparable with entire crystallites can be studied with DMC simulations. Consideration of these longer
length and time scales is necessary for applications of such systems in chemical separations and heterogeneous catalysis. |
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Keywords: | Diffusion Molecular traffic control Zeolites Molecular simulation |
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