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
Physics, photosynthesis and solar cells
01.12.2016 | University of California - Riverside
New process produces hydrogen at much lower temperature
01.12.2016 | Waseda University
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.
The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...
Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water
In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...
The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.
Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
02.12.2016 | Medical Engineering
02.12.2016 | Agricultural and Forestry Science
02.12.2016 | Physics and Astronomy