Abstract

Alloying metals to form intermetallics has been proven effective in tuning the chemical properties of metal-based catalysts. However, intermetallic alloys can undergo structural and chemical transformations under reactive conditions, leading to changes in their catalytic function. Elucidating and understanding these transformations are crucial for establishing relevant structure-performance relationships and for the rational design of alloy-based catalysts. In this work, we used CuZn alloy nanoparticles (NPs) as a model material system and employed in situ transmission electron microscopy (TEM) to investigate the structural and chemical changes of CuZn NPs under H₂, O₂ and their mixture. Our results show how CuZn NPs undergo sequential transformations in the gas mixture at elevated temperatures, starting with gradual leaching and segregation of Zn, followed by oxidation at the NP surface. The remaining copper at the core of particles can then engage in dynamic behavior, eventually freeing itself from the zinc oxide shell. The structural dynamics arises from an oscillatory phase transition between Cu and Cu₂O and is correlated with the catalytic water formation, as confirmed by in situ mass spectrometry (MS). Under pure H₂ or O₂ atmosphere, we observe different structural evolution pathways and final chemical states of CuZn NPs compared to those in the gas mixture. These results clearly demonstrate that the chemical state of alloy NPs can vary considerably under reactive redox atmospheres, particularly for those containing elements with distinct redox properties, necessitating the use of in situ or detailed ex situ characterizations to gain relevant insights into the states of intermetallic alloy-based catalysts and structure-activity relationships.

中文翻译：

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CuZn 合金纳米粒子在反应性氧化还原气氛下的结构和化学转变：原位 TEM 研究

摘要

事实证明，将金属合金化形成金属间化合物可以有效调节金属基催化剂的化学性能。然而，金属间合金在反应条件下会发生结构和化学转变，导致其催化功能发生变化。阐明和理解这些转变对于建立相关的结构-性能关系以及合金基催化剂的合理设计至关重要。在这项工作中，我们使用CuZn合金纳米粒子（NPs）作为模型材料系统，并采用原位透射电子显微镜（TEM）研究了CuZn NPs在H ₂、O ₂及其混合物下的结构和化学变化。我们的结果表明，CuZn 纳米颗粒如何在高温下在气体混合物中经历顺序转变，首先是锌的逐渐浸出和偏析，然后是纳米颗粒表面的氧化。然后，颗粒核心剩余的铜可以参与动态行为，最终从氧化锌壳中释放出来。正如原位质谱 (MS)所证实的，结构动力学源自 Cu 和 Cu ₂ O之间的振荡相变，并且与催化水的形成相关。在纯H ₂或O ₂气氛下，我们观察到CuZn NPs 与气体混合物中不同的结构演化途径和最终化学状态。这些结果清楚地表明，合金纳米粒子的化学状态在反应性氧化还原气氛下可能会发生很大变化，特别是对于那些含有具有不同氧化还原性质的元素的合金纳米粒子，需要使用原位或详细的非原位表征来获得对金属间合金状态的相关见解基于催化剂和结构-活性关系。