In metal-containing zeolites, sintering and redispersion processes exercise control over the identity of metal site structures, but the thermodynamic and kinetic factors that influence these molecular-level processes are not completely understood. Here, we assess the ability of first principles informed free energy models (for supported and unsupported nanoparticles) and kinetic models integrating Ostwald ripening with atom trapping to describe the interconversion between Pt cations and nanoparticles encapsulated in chabazite (CHA) zeolites. Density functional theory-derived thermodynamic phase diagrams show that the interconversion between cations, favored in oxidizing environments, and particles, favored in reducing environments, is fully reversible within a wide range of their respective conditions (temperatures and pressures) for CHA and several other zeolite topologies. Kinetic Monte Carlo simulations of Pt redispersion are consistent with experimentally observed redispersion kinetics of encapsulated Pt nanoparticles in CHA zeolites, and model results suggest the zeolite host imparts additional stability for Pt nanoparticles. We envision our thermodynamic and kinetic models for Pt-CHA are also capable of describing nanoparticle and cation interconversions for other zeolite frameworks under similar conditions.

中文翻译：

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铂纳米颗粒与沸石中阳离子相互转化的热力学和动力学


在含金属沸石中，烧结和再分散过程对金属位点结构的特性进行控制，但影响这些分子水平过程的热力学和动力学因素尚未完全了解。在这里，我们评估了基于第一性原理的自由能模型（对于有支撑和无支撑的纳米颗粒）和将奥斯特瓦尔德熟化与原子捕获相结合的动力学模型来描述 Pt 阳离子和封装在菱沸石 (CHA) 沸石中的纳米颗粒之间相互转化的能力。密度泛函理论导出的热力学相图表明，对于 CHA 和其他几种沸石，氧化环境中有利的阳离子与还原环境中有利的颗粒之间的相互转化在各自的条件（温度和压力）范围内是完全可逆的拓扑。 Pt 再分散的动力学蒙特卡罗模拟与实验观察到的 CHA 沸石中封装的 Pt 纳米颗粒的再分散动力学一致，模型结果表明沸石主体赋予 Pt 纳米颗粒额外的稳定性。我们预计 Pt-CHA 的热力学和动力学模型也能够描述类似条件下其他沸石框架的纳米颗粒和阳离子相互转化。