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Revealing the Atomic Surface Structures of CeO2 Nanocrystals via
High Resolution Electron Microscopy

Scientific Achievements: 
The (100), (110), and (111) surface structures of CeO2 nanoparticles were determined at atomic resolution including the O atoms using aberration corrected high resolution electron microscopy.

Significance and Impact:
“Seeing is believing”, direct observation of the atomic surface structures of CeO2 nanoparticles for the first time provide insight into the shape-selective catalysis of CeO2 nanoparticles.

Research Details:

•  The (100) surface has Ce, O and reduced CeO terminations on the outermost surface as well as the partially occupied atom positions in the near-surface region (~1 nm from the surface).

•  The (110) surface has a combination of reduced flat CeO2-x outermost surface layers and “sawtooth-like” (111) nanofacets.

•  The (111) surface is O layer terminated.

•  The surface results derived from the High Resolution Electron Microscopy (HREM) study are consistent with our infrared spectroscopy study.

Figure 1Figure b

The HREM images show the atomic surface structures of different facets.
The spots in HREM images can be interpreted: the atomic models are overlaid on the simulated images.

 

Additional Description:
Atomic surface structures of CeO2 are of particular interest in chemical and electrochemical catalysis. The previous surface studies on CeO2 are either not on nanoparticles or incapable of “seeing” the O atoms. As a result, the conclusions are often contradictory. In this work, we determined the (100), (110) and (111) surfaces of CeO2 nanocubes at atomic resolution including the O atoms using aberration corrected high resolution electron microscopy. For the predominantly exposed high energy (100) surface, we directly observed the presence of Ce, O and reduced CeO terminations on the outermost surface as well as the partially occupied atoms in the near-surface region (~1 nm from the surface). The previously often assumed CeO termination of the (100) surface is oversimplified. For the (110) surface, there is a combination of reduced flat CeO2-x outermost surface layers and “saw-like” (111) nanofacets. For the (111), the surface is O layer terminated. Furthermore, all the surface results derived from the HREM study are consistent with our infrared spectroscopy study.

Credit:
This work was published by Yuyuan Lin, Zili Wu, Jianguo Wen, Kenneth R. Poeppelmeier and Laurence D. Marks, Nano Letters, (2013) DOI:10.1021/nl403713b. Research sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy. 

 

Surface Chemistry and Catalysis R&D Projects

Provided by Oak Ridge National Laboratory's Chemical Sciences Division
Rev:   December 2013