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Science 5 September 2008:
Vol. 321. no. 5894, pp. 1331 - 1335
DOI: 10.1126/science.1159639
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Reports

Identification of Active Gold Nanoclusters on Iron Oxide Supports for CO Oxidation

Andrew A. Herzing1,2, Christopher J. Kiely1*, Albert F. Carley3, Philip Landon3 and Graham J. Hutchings3*

1 Center for Advanced Materials and Nanotechnology, Lehigh University, 5 East Packer Avenue, Bethlehem, PA 18015–3195, USA.
2 National Institute of Standards and Technology, Surface and Microanalysis Science Division, 100 Bureau Drive, Mailstop 8371, Gaithersburg, MD 20899–8371, USA.
3 Cardiff Catalysis Institute School of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK.


Figure 1 Fig. 1. Low-magnification aberration-corrected HAADF-STEM images from (A) the inactive, tube furnace catalyst (sample 1) and (B) the highly active, GC oven catalyst (sample 2). Au particle size distribution in both samples appears to be very similar at this magnification. [View Larger Version of this Image (61K GIF file)]
 

Figure 2 Fig. 2. High-magnification aberration-corrected STEM-HAADF images of (A and B) the inactive (sample 1) and (C and D) the active (sample 2) Au/FeOx catalysts acquired with the aberration-corrected JEOL 2200FS. The white circles indicate the presence of individual Au atoms, whereas the black circles indicate subnanometer Au clusters consisting of only a few atoms. Note the presence and image intensity difference of two distinct cluster-types: In (C) there are 0.5 nm higher-contrast clusters, whereas in (D) 0.2- to 0.3-nm low-contrast clusters dominate. This difference indicates that bilayer and monolayer subnanometer Au clusters are present in the active catalyst. [View Larger Version of this Image (191K GIF file)]
 

Figure 3 Fig. 3. Aberration-corrected STEM-HAADF images of the active 2.9 atomic % Au/FeOx catalyst 2 calcined for 3 hours at (A and B) 400°C (sample 3), (C and D) 550°C (sample 4), and (E and F) 600°C (sample 5). The heat-treatment procedures have substantially decreased the population of subnanometer Au clusters relative to the highly active, dried catalyst, while at the same time they have increased the population of particles in the 1- to 3-nm range. [View Larger Version of this Image (110K GIF file)]
 

Figure 4 Fig. 4. Relative populations of (i) dispersed Au atoms, (ii) 0.2- to 0.3-nm monolayer Au clusters, (iii) 0.5-nm bilayer Au clusters, and (iv) Au nanoparticles >1 nm in diameter, as a function of catalyst calcination temperature and measured CO conversion. The error bars correspond to two SDs on the size measurements. [View Larger Version of this Image (30K GIF file)]
 

Figure 5 Fig. 5. O(1s) photoemission spectra from the Au/Fe2O3 catalysts (A) dried at 120°C and then calcined at (B) 400°C, (C) 550°C, and (D) 600°C. [View Larger Version of this Image (17K GIF file)]
 

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Science. ISSN 0036-8075 (print), 1095-9203 (online)