Diffusion of pentane isomers in faujasite-type zeolites : NMR and molecular dynamics study

Rajappa, Chitra and Krause, C and Borah, BJ and Adem, Z and Galvosas, P and Kaerger, J and Subramanian, Y (2013) Diffusion of pentane isomers in faujasite-type zeolites : NMR and molecular dynamics study. In: MICROPOROUS AND MESOPOROUS MATERIALS, 171 . pp. 58-64.

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Abstract

Diffusion of pentane isomers in zeolites NaX has been investigated using pulsed field gradient nuclear magnetic resonance (PFG-NMR) and molecular dynamics (MD) techniques respectively. Temperature and concentration dependence of diffusivities have been studied. The diffusivities obtained from NMR are roughly an order of magnitude smaller than those obtained from MD. The dependence of diffusivity on loading at high temperatures exhibits a type I behavior according to the classification of Karger and Pfeifer 1]. NMR diffusivities of the isomers exhibit the order D(n-pentane) > D(isopentane) > D(neopentane). The results from MD suggest that the diffusivities of the isomers follow the order D(n-pentane) < D(isopentane) < D(neopentane). The activation energies from NMR show E-a(n-pentane) < E-a(isopentane) < E-a(neopentane) whereas those from MD suggest the order E-a(n-pentane) > (isopentane) > E-a(neopentane). The latter follows the predictions of levitation effect whereas those of NMR appears to be due to the presence of defects in the zeolite crystals. The differences between diffusivities estimated by NMR and MD are attributed to the longer time and length scales sampled by the NMR technique, as compared to MD. (C) 2012 Elsevier Inc. All rights reserved.

Item Type:	Journal Article
Publication:	MICROPOROUS AND MESOPOROUS MATERIALS
Publisher:	ELSEVIER SCIENCE BV
Additional Information:	Copyright for this article belongs to the ELSEVIER SCIENCE BV, NETHERLANDS.
Keywords:	Diffusion; Zeolite; NMR; Simulation; Concentration dependence
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	23 Apr 2013 06:18
Last Modified:	23 Apr 2013 06:18
URI:	http://eprints.iisc.ac.in/id/eprint/46426

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