Aging mechanisms of nanoceria and pathways for preserving optimum morphology
Aging mechanisms of nanoceria and pathways for preserving optimum morphology
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纳米陶瓷的老化机制和保持最佳形态的途径
DOI：
10.1016/j.nantod.2023.101916
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发表时间：
2023
期刊：
影响因子：
17.4
通讯作者：
Sayle D
中科院分区：
文献类型：
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作者：
Sayle D
热老化可以通过结构变化来改变纳米材料的独特性质。从机理上理解老化过程，包括高温操作条件下的加速老化，是通过控制、限制或抑制与老化相关的过程来实现财产保护的第一步。在这里，我们使用分子动力学来模拟纳米CeO_3立方体和纳米棒的热老化，它们转变为纳米多面体；同时还给出了与实验的电子显微镜图像的比较。我们发现，形态的变化是通过CexOy表面团簇从纳米陶瓷的一个部分到另一个部分的湍流迁移性进行的。对于纳米棒和纳米立方体，具有催化重要性的{100}和{110}表面被侵蚀，而{111}表面的相对面积增加。对模拟的详细分析表明，CexOy星团中的原子并不都同时运动。相反，(-O-Ce-O-Ce-O-)n‘链(较大的CexOy簇的子集)以集体运动的方式运动，而链中的原子以“蠕虫”的方式运动。这降低了与链中所有原子同时进入激活(鞍点)构型相关的激活能垒。我们预测，由氧空位补偿电荷的Gd掺杂的CeO2纳米立方体，比未掺杂和完全氧化的CeO2纳米立方体老化更快。特别是，提高催化活性的掺杂剂也可能通过引入氧空位来加速老化，这些空位将(-O-Ce-O-O-Ce-O-)链断裂成活化能降低的更小的链。因此，我们主张，当使用掺杂来赋予催化活性时，实验也应该针对表面(-O-Ce-O-O-Ce-O-)核链的集体运动，以最大化热稳定性。
Thermal aging can modify the unique properties of a nanomaterialviastructural change. Mechanistic understanding of the aging process, including accelerated aging under high-temperature operating conditions, is a first step towards property preservationviacontrolling, limiting, or suppressing aging-related processes. Here, we use molecular dynamics to simulate thermal aging of ceria nanocubes and nanorods, which transform into nanopolyhedra; comparisons with experimental TEM images are presented alongside. We find that morphology changes proceedviathe turbulent mobility of CexOysurface clusters from one part of the nanoceria to another. For nanorods and nanocubes, catalytically important {100} and {110} surfaces are eroded, whereas the relative area of {111} surfaces increase. Detailed analysis of the simulations reveals that atoms in the CexOyclusters do not all move simultaneously. Rather, (-O-Ce-O-Ce-O-)n‘chains’ (subsets of the larger CexOyclusters) move with collective motion, while the atoms inside the chains move in a ‘worm-like’ fashion. This reduces the activation energy barrier associated with all the atoms in the chain simultaneously moving into an activated (saddle point) configuration. We predict gadolinium-doped ceria nanocubes, charge-compensated by oxygen vacancies, age faster than undoped and fully oxidised ceria nanocubes. In particular, dopants that increase catalytic activity, may also accelerate aging by introducing oxygen vacancies that break the (-O-Ce-O-Ce-O-)nchains into smaller chains with reduced activation energies. Accordingly, we advocate that when doping is used to confer catalytic activity, experiment should also target the collective motion of surface (-O-Ce-O-Ce-O-)nchains to maximise thermal stability.