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Issue 9, 2018
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Metastable morphological states of catalytic nanoparticles

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During the catalytic synthesis of graphene, nanotubes, fibers, and other nanostructures, many intriguing phenomena occur, such as phase separation, precipitation, and analogs of capillary action. Here, we demonstrate, using in situ, real-time transmission electron microscope imaging and modeling, that the catalytic nanoparticles display functional, metastable states, reminiscent of some protein ensembles in vivo. As a carbon nanostructure grows, the nanoparticle elongates due to an energetically favorable metal–carbon interaction that overrides the surface energy increase of the metal. The formation of subsequent nested tubes, however, drives up the particle's free energy, but the particle remains trapped until an accessible free energy surface allows it to exit the tube. During this time, the nanoparticle continues to catalyze tube growth internally to the nested structure. This universal nonequilibrium thermodynamic cycle of elongation and retraction is heavily influenced by tapering of the structure, which, ultimately, determines the final product and catalyst lifetime. Our results provide a unifying framework to interpret similar phenomena for other catalytic reactions, such as during CO oxidation and boron nitride tube growth, and suggest routes to the practical optimization of such processes.

Graphical abstract: Metastable morphological states of catalytic nanoparticles

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The article was received on 16 Nov 2017, accepted on 01 Feb 2018 and first published on 01 Feb 2018

Article type: Paper
DOI: 10.1039/C7NR08579F
Citation: Nanoscale, 2018,10, 4528-4537
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    Metastable morphological states of catalytic nanoparticles

    P. Ann Lin, B. Natarajan, M. Zwolak and R. Sharma, Nanoscale, 2018, 10, 4528
    DOI: 10.1039/C7NR08579F

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