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Migration of zeolite-encapsulated Pt and Au under reducing environments

机译：在还原环境下，沸石封装的PT和AU的迁移

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The encapsulation of noble metal atoms into zeolites is a promising route to generate controlled size distributions of stable metal catalysts. Pinning of single metal atoms to particular binding sites represents the optimal atom-efficiency and is a desirous outcome, despite the propensity of metal clusters to sinter. Currently, sintering resistance of noble metals in siliceous and high-silica frameworks is incompletely understood, while the role of influencing factors such as adsorbates and metal element identity, have not been ascertained. Here, we investigate the nature of metal–zeolite interactions, via density functional global structure optimisation and kinetic Monte Carlo simulations of the binding and migration of Pt and Au in a siliceous zeolite with framework topology LTA. We show that strong binding of Pt atoms to the framework severely hinders migration, even in the absence of framework heteroatoms, while Au diffuses freely through the pore. Reducing agents CO and H2 change the preferred binding site of Pt and flatten the potential energy surface, which reduces migration barriers and thereby promotes particle growth. PtCO is found to represent a compromise between strongly framework-bound Pt1, and bulky, volatile Pt(CO)x clusters, exhibiting fast diffusion. This work provides an atomistic picture of single metal atom kinetics inside high-silica zeolites, which represent a fundamental basis for understanding nano-catalyst deactivation.
机译：贵金属原子封装到沸石中是产生稳定金属催化剂的受控尺寸分布的有前途的途径。将单个金属原子固定到特定的结合位点代表了最佳原子效率，尽管金属簇倾向于烧结，但仍是一个渴望的结果。目前，尚未确定硅质金属在硅质和高硅框架中的烧结抗性，而尚未确定影响因素（如吸附物和金属元素身份）的作用。在这里，我们通过密度功能全局结构优化和动力学蒙特卡洛模拟PT和AU在硅质沸石中与框架拓扑LTA中Pt和Au的结合和迁移来研究金属与氮醇相互作用的性质。我们表明，即使在没有框架杂原子的情况下，PT原子与框架的强大结合也会严重阻碍迁移，而AU则通过孔自由扩散。还原剂CO和H2改变了PT的首选结合位点，并使势能表面变平，从而降低了迁移障碍，从而促进了颗粒的生长。发现PTCO代表了强大的框架结合的PT1和笨重的挥发性PT（CO）X簇之间的折衷，表现出快速扩散。这项工作提供了高硅沸石内部金属原子动力学的原子图，这是理解纳米催化剂失活的基本基础。

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