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Behavior of Au Species in Au/Fe2O3 Catalysts Characterized by Novel In Situ Heating Techniques and Aberration-Corrected STEM Imaging

Published online by Cambridge University Press:  22 June 2010

Lawrence F. Allard ,
Maria Flytzani-Stephanopoulos  and
Steven H. Overbury
Lawrence F. Allard*
Affiliation:
Physical Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
Maria Flytzani-Stephanopoulos
Affiliation:
Department of Chemical and Biological Engineering, Tufts University, Medford, MA 02155, USA
Steven H. Overbury
Affiliation:
Physical Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
*
Corresponding author. E-mail: allardLFjr@ornl.gov
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Abstract

The recent advent of a novel design of in situ heating technology for electron microscopes has permitted unprecedented control of elevated temperature studies of catalytic materials, particularly when coupled with the sub-Ångström imaging performance of a modern aberration-corrected scanning transmission electron microscope (STEM). Using micro-electro-mechanical-systems (MEMS)-based Aduro™ heating chips from Protochips, Inc. (Raleigh, NC, USA) allows nearly instantaneous heating and cooling of catalyst powders, avoiding effects of temperature ramping as experienced with standard heating stages. The heating technology also provides stable operation limited only by the inherent drift in the microscope stage, thus allowing full image resolution to be achieved even at elevated temperatures. The present study details the use of both the high X-Y spatial resolution in both dark-field and simultaneous bright-field imaging, along with the high resolution in Z (depth sectioning) provided by the large probe incidence semiangle in the aberration-corrected instrument, to characterize the evolution of microstructure in a commercial Au/Fe2O3 water-gas shift catalyst during elevated temperature treatment. The phenomenon of Au diffusion to the surface of hematite support particles to form discrete crystalline Au nanoparticles in the 1–2 nm size range, after a prior leaching treatment to remove surface Au species has been characterized.

Keywords

STEMaberration correctionin situAu catalystsdepth sectioningHAADF
Type
Special Section—Aberration-Corrected Electron Microscopy
Information
Microscopy and Microanalysis , Volume 16 , Issue 4 , August 2010 , pp. 375 - 385
Copyright
Copyright © Microscopy Society of America 2010

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References

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