A molecular dynamics investigation of a variety of influences of temperature on diffusion in zeolites

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• 作者：R. Krishna ; J.M. van Baten
• 关键词：Maxwell– ; Stefan diffusivity ; Self diffusivity ; Molecular dynamics ; Zeolites ; Activation energy ; Loading dependence ; Correlations
• 刊名：Microporous and Mesoporous Materials
• 出版年：2009
• 出版时间：1 October 2009
• 年：2009
• 卷：125
• 期：1-2
• 页码：126-134
• 全文大小：1330 K

文摘

Molecular dynamics (MD) simulations were performed to determine both the Maxwell–Stefan diffusivity, Đ_i, and the self-diffusivity, D_i,self, of a variety of molecules (Ne, Ar, Kr, CH₄, C₂H₄, CO₂, O₂, and N₂) in five different zeolites (LTA, DDR, CHA, FAU, MFI) for a range of temperatures, T, and molecular loadings, q_i. The simulation results show that for cage-type zeolites with narrow windows (LTA, CHA, and DDR) with guest molecules such as CH₄ and Kr, that are tightly constrained at the window regions, the Đ_i − q_i dependence varies significantly with T. Furthermore, the activation energy changes with the loading q_i. The model of Reed and Ehrlich (D.A. Reed, G. Ehrlich, Surf. Sci. 102 (1981) 588) provides a convenient description of the combined influence of q_i and T on Đ_i. For other guest–host combinations that were investigated the Đ_i − q_i dependence was found to depend relatively weakly on T. The strength of correlations, quantified by (Đ_i/D_i,self − 1) is found to be practically T-independent for all guest–host combinations examined. Generally speaking, for a specified loading q_i, the activation energy for Đ_i − T and D_i,self − T variations are different; the difference is about 10 % when the strength of correlations is large.