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Dopants Adsorbed as Single Atoms Prevent Degradation of Catalysts

A. Y. Borisevich1, S. J. Pennycook1, S. Wang2, S. N. Rashkeev2, S. T. Pantelides2, M. V. Glazoff3, K. Sohlberg4

Nature Materials, 3, 143 (2004)

Full Article (PDF 372 KB)

The aberration-corrected 300 kV scanning transmission electron microscope at ORNL now produces the world's smallest beam, 0.7 Å diameter, providing unprecedented sensitivity for imaging single atoms. Lanthanum (La) is used as a dopant to stabilize commercial catalysts, but the mechanism was unknown. The new sensitivity has revealed isolated La atoms on the alumina surface. First-principles calculations show strong binding to a gamma alumina surface, the desired form of catalyst support, but binding to alpha alumina is much weaker. Conversion of the support from gamma to alpha is therefore retarded when La is present. The catalyst survives longer at high temperature, bringing economic, energy and environmental benefits.

 
 






Figure 1: (a) STEM image of La atoms on off-axis flake of γ-Al2O3 (b) corresponding size distribution histogram with maximum at ~0.7-0.8Å.
Figure 2: Dynamical simulation of La atom images shows those on the bottom surface are brightest (yellow), those on the top are less bright (blue) and interstitials are weakest (green).
   
 
  1. Condensed Matter Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
  2. Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, USA
  3. Alcoa Technical Center, Alcoa Center, Pennsylvania 15069-0001, USA
  4. Department of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104, USA

 Oak Ridge National Laboratory