Atom-Resolved Imaging of Dynamic Shape Changes in Supported Copper Nanocrystals

Abstract

In situ transmission electron microscopy is used to obtain atom-resolved images of copper nanocrystals on different supports. These are catalysts for methanol synthesis and hydrocarbon conversion processes for fuel cells. The nanocrystals undergo dynamic reversible shape changes in response to changes in the gaseous environment. For zinc oxide-supported samples, the changes are caused both by adsorbate-induced changes in surface energies and by changes in the interfacial energy. For copper nanocrystals supported on silica, the support has negligible influence on the structure. Nanoparticle dynamics must be included in the description of catalytic and other properties of nanomaterials. In situ microscopy offers possibilities for obtaining the relevant atomic-scale insight.

Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions

“…Prominent examples in which TEM was used to gain insights into dynamic structure changes of catalysts are the restructurings of Cu surfaces of a Cu/ZnO catalyst in different gas atmospheres (see also Figures 5 and 6),46, 47 carbon nanofiber growth on a Ni catalyst during methane decomposition,14 and the refacetting of Pt nanocrystals during CO oxidation in a nanoreactor at 1 bar and at elevated temperatures 89…”

“…Systems composed of several components often feature strong metal–support interactions. Changing redox potentials of the reaction mixtures may lead to differing adhesion between metal particles and the oxide support, which in turn might result in morphological changes (Figure 4 d),13, 46 or decoration effects47, 48, 49, 50 on the metal surface. In extreme cases this may lead to composite formation (Figure 4 c) 51…”

“…With the help of operando EXAFS,13 in situ IR spectroscopy,57 and in situ electron microscopy46 morphological changes induced by different reaction atmospheres could be detected (Figure 5). Formation of metallic Zn was recently evidenced by titration and electron microscopy corroborated by DFT‐calculations 58.…”

In Situ Industrial Bimetallic Catalyst Characterization using Scanning Transmission Electron Microscopy and X‐ray Absorption Spectroscopy at One Atmosphere and Elevated Temperature

“…Although these results are encouraging, recent work has demonstrated that surface structures can vary dramatically in UHV environments from those appropriate to the working conditions of industrial catalysts 20. This has led to an explosion of interest in in situ TEM, where materials are studied under more realistic environmental conditions 21, 22, 23.…”

“…Since different nanoparticle structures may have varying catalytic activity,13 an understanding of the different particle types observed gives additional insight into catalytic performance. This is particularly important in cases where particle morphology is affected by the environment 20, 21, 22. In systems such as these, in situ high spatial resolution EDS is required to observe the true nanostructures and their compositional distribution as shown in Figure 3 f. …”