Imaging of cerium oxide nanocrystals provides insights into the different behaviors of catalyst for emission control, other uses.
When it comes to reducing the toxins released by burning gasoline, coal, or other such fuels, the catalyst needs to be reliable. Yet, a promising catalyst, cerium dioxide (CeO2), seemed erratic. The catalyst’s three different surfaces behaved differently.
Image courtesy of Northwestern University
The image on the left shows the general shape of a cubic cerium dioxide nanoparticle. The images on the right show edge-on views of three exposed surfaces at atomic resolution. The atomic models are overlaid on the simulated images to illustrate atom positions.
For the first time, researchers got an atomically resolved view of the three structures, including the placement of previously difficult-to-visualize oxygen atoms. This information may provide insights into why the surfaces have distinct catalytic properties.
Solving the three different atomic surface structures of CeO2 nanoparticles provides insight into how to potentially control the morphology of the nanoparticles to improve catalytic selectivity, activity and stability. This knowledge provides an opportunity to potentially improve the catalytic properties of CeO2 nanoparticles in catalytic converters in vehicles and other applications.
Cerium oxide (CeO2) nanoparticles are widely used in chemical catalysis. Typical CeO2 catalytic nanoparticles have three main surfaces exposed: (100), (110) and (111). Previous studies show that the differing catalytic properties of each surface are closely related to the atomic structure of the surface. Unfortunately, scientists had difficulties in visualizing the oxygen atoms that pack these surfaces.
The challenge was overcome by a team of researchers at Northwestern University, Oak Ridge National Laboratory, and Argonne National Laboratory. The researchers determined the surface structures using the most advanced chromatic and spherical aberration-corrected electron microscope at Argonne National Laboratory. The microscope enables clear imaging of both cerium and oxygen atoms.
For the high energy (100) surface, the presence of cerium, oxygen, and reduced cerium oxide terminations on the outermost surface as well as the partially occupied lattice sites in the near-surface region (~1 nm from the surface) were directly observed. The disordered surface demonstrates that the previous understanding of the (100) surface was oversimplified.
For the (110) surface, a combination of reduced flat CeO2-x surface layers and “sawtooth-like” (111) nanofacets exist. The (111) surface is terminated by an oxygen layer, precisely as anticipated from previous models, and consistent with its high stability.
Further, the surface structures derived from the microscopy study are consistent with results from a macroscopic infrared spectroscopy investigation. The variation in surface defect density between these three facets appears to be responsible for their differences in catalytic activity and potentially opens options to modify faces of CeO2 nanoparticles to develop face selective catalysts.
DOE Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences.
Y. Lin, Z. Wu, J. Wen, K. R. Poeppelmeier, L. D. Marks, “Imaging the atomic surface structures of CeO2 nanoparticles.” Nano Letters 14, 191 (2014). [DOI: 10.1021/nl403713b]
Z. Wu, M. Li, D. R. Mullins, S. H. Overbury, “Probing the surface sites of CeO2 nanocrystals with well-defined surface planes via methanol adsorption and desorption.” ACS Catalysis 2, 2224 (2012). [DOI: 10.1021/cs300467p]
Kristin Manke | newswise
Nano 'sandwich' offers unique properties
28.02.2017 | Rice University
Sustainable ceramics without a kiln
28.02.2017 | ETH Zurich
On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded after a glide flight with an Airbus A320 in ditching on the Hudson River. All 155 people on board were saved.
On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded...
In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
28.02.2017 | Physics and Astronomy
28.02.2017 | Materials Sciences
28.02.2017 | Health and Medicine