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Pressure- and Temperature-Induced Monoclinic-to-Orthorhombic Phase Transition in Silicalite-1
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2018-02-28 00:00:00 , DOI: 10.1021/acs.jpcc.8b00400 Nikolaos Lempesis 1 , Natalia Smatsi 1 , Vlasis G. Mavrantzas 1, 2 , Sotiris E. Pratsinis 1
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2018-02-28 00:00:00 , DOI: 10.1021/acs.jpcc.8b00400 Nikolaos Lempesis 1 , Natalia Smatsi 1 , Vlasis G. Mavrantzas 1, 2 , Sotiris E. Pratsinis 1
Affiliation
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The thermal, mechanical, and volumetric behavior of silicalite-1, an all-silica Mobil Five (MFI) zeolite, is elucidated by atomistic simulations. A flexible force field was selected and validated from a set of force fields to capture the intramolecular interactions of the crystal lattice. This force field accounts for realistic bond, angle, and torsional interactions among atoms of the framework alongside with conventional Lennard-Jones and Coulomb interactions. By monitoring the behavior of silicalite-1 as a function of pressure and temperature, a fully reversible monoclinic-to-orthorhombic phase transition (polymorphism) was revealed in accordance with experimental data. Thermodynamic considerations dictate that this is a second-order phase transition in the Ehrenfest classification. Additionally, reversible pressure-induced amorphization was captured by our model and was associated with the formation of linear zones of increased distortion running parallel to the straight and sinusoidal channels of this zeolite. Remarkably high isothermal compressibility (small bulk modulus) was calculated for orthorhombic silicalite-1, in excellent agreement with experimental data, rendering silicalite-1 as the most compressible zeolite known to date. The rigid unit mode model was identified as the dominant structural mechanism for negative thermal expansion (NTE), typically observed over a wide temperature range in MFI zeolites. Better understanding of the monoclinic-to-orthorhombic phase transition and molecular mechanisms associated with energy dissipation and NTE in zeolites provides control over the framework microstructure, allowing for enhanced molecular sieving, tunable selectivity in separation processes, mechanical stability, and substantially amplified catalytic efficiency in petrochemical applications.
中文翻译：
Silicalite-1中压力和温度诱导的单斜晶向正交晶相转变
通过原子模拟来阐明了全硅Mobil Five（MFI）沸石Siliconelite-1的热，机械和体积行为。从一组力场中选择并验证了一个柔性力场，以捕获晶格的分子内相互作用。该力场说明了框架原子之间的实际键合，角度和扭转相互作用，以及常规的Lennard-Jones和库仑相互作用。通过监测作为压力和温度的函数的silicalite-1的行为，根据实验数据揭示了完全可逆的单斜晶向斜方晶相转变（多态性）。热力学因素表明，这是埃伦菲斯特（Ehrenfest）分类中的二级相变。此外，可逆压力诱导的非晶化被我们的模型捕获，并与线性增加的畸变线性区域的形成相关，该线性区域平行于该沸石的直通道和正弦通道延伸。正交晶硅沸石-1计算出的等温压缩率极高（小体积模量），与实验数据高度吻合，使硅沸石-1成为迄今为止已知的最易压缩的沸石。刚性单位模式模型被确定为负热膨胀（NTE）的主要结构机制，通常在MFI沸石的宽温度范围内观察到。更好地了解单斜晶向斜方晶的相变以及与分子中的能量耗散和NTE相关的分子机理，可以控制骨架的微观结构，
更新日期：2018-02-28
中文翻译：
Silicalite-1中压力和温度诱导的单斜晶向正交晶相转变
通过原子模拟来阐明了全硅Mobil Five（MFI）沸石Siliconelite-1的热，机械和体积行为。从一组力场中选择并验证了一个柔性力场，以捕获晶格的分子内相互作用。该力场说明了框架原子之间的实际键合，角度和扭转相互作用，以及常规的Lennard-Jones和库仑相互作用。通过监测作为压力和温度的函数的silicalite-1的行为，根据实验数据揭示了完全可逆的单斜晶向斜方晶相转变（多态性）。热力学因素表明，这是埃伦菲斯特（Ehrenfest）分类中的二级相变。此外，可逆压力诱导的非晶化被我们的模型捕获，并与线性增加的畸变线性区域的形成相关，该线性区域平行于该沸石的直通道和正弦通道延伸。正交晶硅沸石-1计算出的等温压缩率极高（小体积模量），与实验数据高度吻合，使硅沸石-1成为迄今为止已知的最易压缩的沸石。刚性单位模式模型被确定为负热膨胀（NTE）的主要结构机制，通常在MFI沸石的宽温度范围内观察到。更好地了解单斜晶向斜方晶的相变以及与分子中的能量耗散和NTE相关的分子机理，可以控制骨架的微观结构，
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