Temperature Dependence of Volume Change of NaX and NaY Zeolites Using Molecular Dynamics Simulations

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• 作者：Hyein Guk ; Daejin Kim ; Heeju Lee ; Yong Nam Choi ; Sun Young Kang ; Seung-Hoon Choi ; Dong Hyen Chung
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：June 19, 2014
• 年：2014
• 卷：118
• 期：24
• 页码：12811-12816
• 全文大小：299K
• 年卷期：v.118,no.24(June 19, 2014)
• ISSN：1932-7455

文摘

The thermal expansion behavior of faujasite zeolites, dealuminated Y (DAY), NaX, and NaY, has been studied by means of molecular dynamics (MD) simulations. In this work, harmonic potential parameters for the bond stretching and the angle bending are optimized for the MD simulations. The simulation results show that DAY and NaY monotonously contract over the entire temperature range 50鈥?00 K, but the coefficient of thermal expansion of DAY is a more negative value (鈭?.2 脳 10^鈥? K^鈥?) than that of NaY (鈭?.9 脳 10^鈥? K^鈥?). On the other hand, NaX contracts up to room temperature and expands upon further heating. The analysis of bond lengths and angles shows that the volume change behaviors are highly correlated to the bond angle changes with temperature. The nonmonotonous volume change behavior of NaX is also directly related to the bond angle changes. From the radial distribution function of Na⁺ ions, we found that the highly concentrated Na⁺ ions in NaX can exert repulsive forces on each other, such that the volume change direction above room temperature can be reversed.