蒙脱石粘土-沸石复合材料中封闭反应水的动力学,Journal of the American Chemical Society

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蒙脱石粘土-沸石复合材料中封闭反应水的动力学
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2012-02-01 , DOI: 10.1021/ja208894m
Michael C. Pitman ₁ , Adri C. T. van Duin ₂

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限制在膨胀粘土和沸石等矿物中介孔区域的水的动力学是影响全球范围内许多过程的广泛资源管理问题的基础，包括放射性废物遏制、海水淡化和提高石油采收率。限制在硅沸石笼中的低水合条件下自由扩散的多层蒙脱石颗粒的大规模原子模型用于研究复合环境中的水动力学，其中 ReaxFF 反应力场在 300-647 K 的温度范围内。力场使一系列相关的表面化学得以出现，包括夹层水合钙中的酸/碱平衡以及粘土边缘和沸石外壳内表面上的硅烷醇形成。退火后，由此产生的粘土模型表现出单层和双层水化结构。粘土表面水化显着重新分布并屈服于硅沸石水负载。我们发现，水动力学的绝对速率和温度依赖性分别与来自 Ca-蒙脱石和硅沸石相关样品的中子散射数据和脉冲场梯度测量结果相比较。在原子的、反应性的背景下，我们的结果将夹层 Ca(OH)(2)·nH(2)O 环境中的水动力学与流过粘土表面的水和硅质岩内扩散的水区分开来。我们发现，当与 Ca 水合物复合时，水的扩散比在粘土表面上自由扩散的水慢得多，

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Dynamics of Confined Reactive Water in Smectite Clay–Zeolite Composites

The dynamics of water confined to mesoporous regions in minerals such as swelling clays and zeolites is fundamental to a wide range of resource management issues impacting many processes on a global scale, including radioactive waste containment, desalination, and enhanced oil recovery. Large-scale atomic models of freely diffusing multilayer smectite particles at low hydration confined in a silicalite cage are used to investigate water dynamics in the composite environment with the ReaxFF reactive force field over a temperature range of 300-647 K. The reactive capability of the force field enabled a range of relevant surface chemistry to emerge, including acid/base equilibria in the interlayer calcium hydrates and silanol formation on the edges of the clay and inner surface of the zeolite housing. After annealing, the resulting clay models exhibit both mono- and bilayer hydration structures. Clay surface hydration redistributed markedly and yielded to silicalite water loading. We find that the absolute rates and temperature dependence of water dynamics compare well to neutron scattering data and pulse field gradient measures from relevant samples of Ca-montmorillonite and silicalite, respectively. Within an atomistic, reactive context, our results distinguish water dynamics in the interlayer Ca(OH)(2)·nH(2)O environment from water flowing over the clay surface, and from water diffusing within silicalite. We find that the diffusion of water when complexed to Ca hydrates is considerably slower than freely diffusing water over the clay surface, and the reduced mobility is well described by a difference in the Arrhenius pre-exponential factor rather than a change in activation energy.

更新日期：2012-02-01

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