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Journal of Electron Microscopy Advance Access published online on April 1, 2009
Journal of Electron Microscopy, doi:10.1093/jmicro/dfp016
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Evolution of gold structure during thermal treatment of Au/FeOx catalysts revealed by aberration-corrected electron microscopy

Lawrence F. Allard1,*, Albina Borisevich1, Weiling Deng2, Rui Si2, Maria Flytzani-Stephanopoulos2 and Steven H. Overbury3

1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6064
2 Department of Chemical and Biological Engineering, Tufts University, Medford, MA 02155
3 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6201, USA

* To whom correspondence should be addressed. E-mail: allardLFjr{at}ornl.gov

High-resolution aberration-corrected electron microscopy was performed on a series of catalysts derived from a parent material, 2 at.% Au/Fe2O3 (WGC ref. no. 60C), prepared by co-precipitation and calcined in air at 400°C, and a catalyst prepared by leaching surface gold from the parent catalyst and exposed to various treatments, including use in the water–gas shift reaction at 250°C. Aberration-corrected JEOL 2200FS (JEOL USA, Peabody, MA) and Vacuum Generators HB-603U STEM instruments were used to image fresh, reduced, leached, used and re-oxidized catalyst samples. A new in situ heating technology (Protochips Inc., Raleigh, NC, USA), which permits full sub-Ångström imaging resolution in the JEOL 2200FS was used to study the effects of temperature on the behavior of gold species. A remarkable stability of gold to redox treatments up to 400°C, with atomic gold decorating step surfaces of iron oxide was identified. On heating the samples in vacuum to 700°C, it was found that monodispersed gold began to sinter to form nanoparticles above 500°C. Gold species internal to the iron oxide support material was shown to diffuse to the surface at elevated temperature, coalescing into discrete nanocrystals. The results demonstrate the value of in situ heating for understanding morphological changes in the catalyst with elevated temperature treatments.

Keywords     aberration-corrected, high-resolution microscopy, gold, iron oxide, water–gas shift catalyst, in situ heating

Received      8 January 2009, accepted 5 March 2009


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