Evolution of Gold Structure During Thermal Treatment of Au/FeOx Catalysts Revealed by Aberration-Corrected Electron Microscopy

Journal Article · Thu Jan 01 04:00:00 EST 2009 · Journal of Electron Microscopy

OSTI ID:972017

Allard, Jr, Lawrence Frederick ^[1]; Borisevich, Albina Y ^[1]; Deng, Weiling ^[2]; Si, Rui ^[2]; Flytzani-Stephanopoulos, Prof. Maria ^[2]

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1. ORNL
2. Tufts University

High-resolution aberration-corrected electron microscopy was performed on a series of catalysts derived from a parent material, 2 at.% Au/Fe{sub 2}O{sub 3} (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-Angstrom 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.

• Research Organization: Oak Ridge National Laboratory (ORNL); Center for Nanophase Materials Sciences; High Temperature Materials Laboratory
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 972017
• Journal Information: Journal of Electron Microscopy, Journal Name: Journal of Electron Microscopy Journal Issue: 3 Vol. 266
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CATALYSTS
GOLD
HEAT TREATMENTS
IRON OXIDES
MORPHOLOGICAL CHANGES