Visualizing the Cu/Cu2O Interface Transition in Nanoparticles with Environmental Scanning Transmission Electron Microscopy
Visualizing the Cu/Cu2O Interface Transition in Nanoparticles with Environmental Scanning Transmission Electron Microscopy
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DOI：
10.1021/jacs.6b08842
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发表时间：
2017-01-11
影响因子：
15
通讯作者：
Boyes, Edward D.
中科院分区：
文献类型：
--
作者：
LaGrow, Alec P.;Ward, Michael R.;Boyes, Edward D.
了解具有催化活性的过渡金属纳米颗粒的氧化和还原机理对于提高其在各种化学过程中的应用是重要的。在纳米催化中，纳米颗粒可以原位进行氧化或还原，因此氧化还原物质不是反应前后观察到的物质。我们使用了新的环境扫描透射电子显微镜（ESTEM）与0.1 nm分辨率的复杂的动态氧化和还原机制的铜纳米粒子的系统研究。先前已经报道铜的氧化取决于其晶体学及其与衬底的相互作用。通过在ESTEM中使用高角度环形暗场成像在真实的时间内原位跟踪动态氧化过程，我们使用理想的条件来跟踪氧化前沿，因为它通过跟踪原子序数（Z）对比度随时间的变化而在铜纳米颗粒上进行。氧化通过氧化物相（Cu 2 O）从纳米颗粒的一个区域成核而发生，然后氧化物相（Cu 2 O）在颗粒上单向前进，其中Cu与Cu 2 O的界面具有Cu{111}//Cu 2 O {111}的关系。氧化动力学与温度和氧分压有关。当该过程在氢气中逆转时，观察到还原过程与氧化过程相似，两相之间具有相同的晶体学关系。动态观察提供了独特的见解氧化还原机制，这是重要的理解和控制的铜基纳米粒子的氧化和还原。
Understanding the oxidation and reduction mechanisms of catalytically active transition metal nano particles is important to improve their application in a variety of chemical processes. In nanocatalysis the nanoparticles can undergo oxidation or reduction in situ, and thus the redox species are not what are observed before and after reactions. We have used the novel environmental scanning transmission electron microscope (ESTEM) with 0.1 nm resolution in systematic studies of complex dynamic oxidation and reduction mechanisms of copper nanoparticles. The oxidation of copper has previously been reported to be dependent on its crystallography and its interaction with the substrate. By following the dynamic oxidation process in situ in real time with high-angle annular dark-field imaging in the ESTEM, we use conditions ideal to track the oxidation front as it progresses across a copper nanoparticle by following the changes in the atomic number (Z) contrast with time. The oxidation occurs via the nucleation of the oxide phase (Cu2O) from one area of the nanoparticle which then progresses unidirectionally across the particle, with the Cu-to-Cu2O interface having a relationship of Cu{111}//Cu2O{111}. The oxidation kinetics are related to the temperature and oxygen pressure. When the process is reversed in hydrogen, the reduction process is observed to be similar to the oxidation, with the same crystallographic relationship between the two phases. The dynamic observations provide unique insights into redox mechanisms which are important to understanding and controlling the oxidation and reduction of copper-based nanoparticles.