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Transport in nanoporous zeolites: Relationships between sorbate size, entropy, and diffusivity

Borah, Bhaskar J and Maiti, Prabal K and Chakravarty, Charusita and Yashonath, S (2012) Transport in nanoporous zeolites: Relationships between sorbate size, entropy, and diffusivity. In: JOURNAL OF CHEMICAL PHYSICS, 136 (17). 174510-1-174510-8.

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Official URL: http://dx.doi.org/10.1063/1.4706520

Abstract

Molecular dynamics simulations have been performed on monatomic sorbates confined within zeolite NaY to obtain the dependence of entropy and self-diffusivity on the sorbate diameter. Previously, molecular dynamics simulations by Santikary and Yashonath J. Phys. Chem. 98, 6368 (1994)], theoretical analysis by Derouane J. Catal. 110, 58 (1988)] as well as experiments by Kemball Adv. Catal. 2, 233 (1950)] found that certain sorbates in certain adsorbents exhibit unusually high self-diffusivity. Experiments showed that the loss of entropy for certain sorbates in specific adsorbents was minimum. Kemball suggested that such sorbates will have high self-diffusivity in these adsorbents. Entropy of the adsorbed phase has been evaluated from the trajectory information by two alternative methods: two-phase and multiparticle expansion. The results show that anomalous maximum in entropy is also seen as a function of the sorbate diameter. Further, the experimental observation of Kemball that minimum loss of entropy is associated with maximum in self-diffusivity is found to be true for the system studied here. A suitably scaled dimensionless self-diffusivity shows an exponential dependence on the excess entropy of the adsorbed phase, analogous to excess entropy scaling rules seen in many bulk and confined fluids. The two trajectory-based estimators for the entropy show good semiquantitative agreement and provide some interesting microscopic insights into entropy changes associated with confinement.

Item Type: Journal Article
Additional Information: copyright for this article belongs to American Institute of Physics
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Division of Physical & Mathematical Sciences > Physics
Date Deposited: 18 Jul 2012 11:48
Last Modified: 18 Jul 2012 11:48
URI: http://eprints.iisc.ernet.in/id/eprint/44659

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