Transition State Theory Based Model for Molecular Anisotropic Diffusion in ITQ-3 Zeolite Narrow Channels

Chem. J. Chinese Universities ›› 2010, Vol. 31 ›› Issue (7): 1431.

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Transition State Theory Based Model for Molecular Anisotropic Diffusion in ITQ-3 Zeolite Narrow Channels

HUO Rui-Xia¹, LIU Jun², YANG Xiao-Feng^1,3*, QIN Zhang-Feng³, WANG Jian-Guo³

1. Department of Physics,
2. Department of Electronics Science and Technology, North University of China, Taiyuan 030051 China;
3. State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China

Received:2009-12-11 Online:2010-07-10 Published:2010-07-10
Contact: YANG Xiao-Feng. E-mail: yangxf@nuc.edu.cn
Supported by:
国家自然科学基金(批准号: 50730009)和山西省自然科学基金(批准号: 2009011001-2)资助.

Abstract

Abstract:

A model of molecular diffusion in the narrow pores of zeolite ITQ-3, which is based on transition-state theory, is proposed. In this model, the movement of molecules is treated as hopping from one adsorption site to another in connected cavities and the potential barriers between them are thought to be large. This assumption could simplify the potential at the windows between the cavities as pure repulsive form, from which the formula for the dependence of diffusion upon temperature and Lennard-Jones parameters can be obtained analytically. The model is compared with molecular dynamics simulations of carbon tetrafluoride CF₄ diffusing on ITQ-3. The diffusion activated energy, the barrier height, and the potential at adsorption sites given by simulations are in accordance with the actual values. This indicates that molecular diffusion behaves in the same way assumed in the model. The simulations also show that the diffusion coefficients first increase and then decrease in response to the loadings. The changes of the activated energy calculated at different loadings have explained this dependence behavior. The increasing of the loading will elevate the potential energy of molecules at cavities, namely lower the activated energy, and consequently give rise to the increasing of diffusion coefficients. Further increasing of the loadings would lead the decreasing trend of the diffusion owing to the blocking effect.

Key words: Molecular dynamics; ITQ-3 zeolite; Diffusion coefficient; Transition-state theory

TrendMD:

HUO Rui-Xia, LIU Jun, YANG Xiao-Feng*, QIN Zhang-Feng, WANG Jian-Guo. Transition State Theory Based Model for Molecular Anisotropic Diffusion in ITQ-3 Zeolite Narrow Channels[J]. Chem. J. Chinese Universities, 2010, 31(7): 1431.

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Transition State Theory Based Model for Molecular Anisotropic Diffusion in ITQ-3 Zeolite Narrow Channels

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