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Visualizing the Cu/Cu2O interface transition in nanoparticles with environmental scanning transmission electron microscopy

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JournalJournal of the American Chemical Society
DateAccepted/In press - 23 Aug 2016
DateE-pub ahead of print - 12 Dec 2016
DatePublished (current) - 11 Jan 2017
Issue number1
Volume139
Number of pages7
Pages (from-to)179-185
Early online date12/12/16
Original languageEnglish

Abstract

Understanding the oxidation and reduction mechanisms of catalytically active transition metal nanoparticles 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 (Cu20) from one area of the nanoparticle which then progresses unidirectionally across the particle, with the Cu-to-Cu20 interface having a relationship of Cu{111}//Cu20{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.

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© 2016 American Chemical Society. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

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