New technique combines electron microscopy and synchrotron X-rays to track chemical reactions under real operating conditions
A new technique pioneered at the U.S. Department of Energy's Brookhaven National Laboratory reveals atomic-scale changes during catalytic reactions in real time and under real operating conditions.
A team of scientists used a newly developed reaction chamber to combine x-ray absorption spectroscopy and electron microscopy for an unprecedented portrait of a common chemical reaction. The results demonstrate a powerful operando technique--from the Latin for "in working condition"--that may revolutionize research on catalysts, batteries, fuel cells, and other major energy technologies.
"We tracked the dynamic transformations of a working catalyst, including single atoms and larger structures, during an active reaction at room temperature," said study coauthor and Brookhaven Lab scientist Eric Stach. "This gives us unparalleled insight into nanoparticle structure and would be impossible to achieve without combining two complementary operando techniques."
The results were published online June 29, 2015, in the journal Nature Communications.
To prove the efficacy of this new mosquito-sized reaction chamber--called a micro-reactor--the scientists tracked the performance of a platinum catalyst during the conversion of ethylene to ethane, a model reaction relevant to many industrial synthesis processes. They conducted x-ray studies at the National Synchrotron Light Source (NSLS) and electron microscopy at the Center for Functional Nanomaterials (CFN), both DOE Office of Science User Facilities.
"The size, shape, and distribution of catalysts affect their efficiency and durability," said study coauthor Ralph Nuzzo of the University of Illinois at Urbana-Champaign. "Now that we can track those parameters throughout the reaction sequence, we can better determine the ideal design of future catalysts--especially those that drive energy-efficient reactions without using expensive and rare materials like platinum."
Hidden behind the curtain
In transmission electron microscopy (TEM), a focused electron beam passes through the sample and captures images of the nanoparticles within. This is usually performed in a pristine environment--often an inactive, low-pressure vacuum--but the micro-reactor allowed the TEM to operate in the presence of an atmosphere of reactive gases.
"With TEM, we take high-resolution pictures of the particles to directly see their size and distribution," said Stach, who leads CFN's Electron Microscopy Group. "But with the micro-reactor, some signals were too small to detect. Particles smaller than a single nanometer were hidden behind what we call the resolution curtain of the technique."
Another technique was needed to peer behind the curtain and reveal the full reaction story: x-ray absorption spectroscopy (XAS).
In XAS, a beam of x-rays bombards the catalyst sample and deposits energy as it passes through the micro-reactor. The sample then emits secondary x-rays, which are measured to identify its chemical composition--in this instance, the distribution of platinum particles.
"The XAS and TEM data, analyzed together, let us calculate the numbers and average sizes of not one, but several different types of catalysts," said coauthor and Yeshiva University scientist Anatoly Frenkel, who led the x-ray experiments. "Running the tests in an operando condition lets us track broad changes over time, and only the combination of techniques could reveal all catalytic particles."
The new micro-reactor was specifically designed and built to work seamlessly with both synchrotron x-rays and electron microscopes.
"Everything was exquisitely controlled at both NSLS and CFN, including precise measurements of the progress of the catalytic reaction," Frenkel said. "For the first time, the operando approach was used to correlate data obtained by different techniques at the same stages of the reaction."
A relatively straightforward mathematical approach allowed them to deduce the total number of ultra-small particles missing in the TEM data.
"We took the full XAS data, which incorporates particles of all sizes, and removed the TEM results covering particles larger than one nanometer--the remainder fills in that crucial sub-nanometer gap in our knowledge of catalyst size and distribution during each step of the reaction," Frenkel said.
Added Stach, "In the past, scientists would look at data before and after the reaction under model conditions, especially with TEM, and make educated guesses. Now we can make definitive statements."
Brighter, faster experiments
The collaboration has already extended this operando micro-reactor approach to incorporate two additional techniques--infrared and Raman spectroscopy--and plans to introduce other complex and complementary x-ray and electron probe techniques over time.
NSLS ended its 32-year experimental run in the fall of 2014, but its successor--the just-opened National Synchrotron Light Source II (NSLS-II)--is 10,000 times brighter and promises to rapidly advance operando science.
"Each round of data collection took six hours at NSLS, but will take just minutes at NSLS-II," Stach said. "Through Laboratory Directed Research and Development funding, we will be part of the initial experiments at the Submicron Resolution X-ray (SRX) Spectroscopy beamline this summer, dramatically increasing the time resolution of the experiments and letting us track changes in a more dynamic fashion. And that's just one of the NSLS-II beamlines where we plan to deploy this technique."
The ethylene to ethane reaction happens at room temperature, but other new micro-reactors can operate at up to 800 degrees Celsius--more than hot enough for most catalytic reactions-- and will increase the versatility and applicability of the approach.
In the near future, this same micro-reactor approach will be used to explore other crucial energy frontiers, including batteries and fuel cells.
"We are seeing the emergence of a very powerful and versatile technique that leverages both NSLS-II and the CFN," said Stach, who was recently named Special Assistant for Operando Experimentation for Brookhaven's Energy Sciences Directorate. "This approach complements the many facilities being developed at Brookhaven Lab for operando energy research. Our goal is to be world leaders in operando science."
Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization.
Justin Eure | EurekAlert!
Innovative LED High Power Light Source for UV
22.06.2017 | Omicron - Laserage Laserprodukte GmbH
Spin liquids − back to the roots
22.06.2017 | Universität Augsburg
Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.
Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...
Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.
As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...
Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.
With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...
Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine
Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...
Germany counts high-precision manufacturing processes among its advantages as a location. It’s not just the aerospace and automotive industries that require almost waste-free, high-precision manufacturing to provide an efficient way of testing the shape and orientation tolerances of products. Since current inline measurement technology not yet provides the required accuracy, the Fraunhofer Institute for Laser Technology ILT is collaborating with four renowned industry partners in the INSPIRE project to develop inline sensors with a new accuracy class. Funded by the German Federal Ministry of Education and Research (BMBF), the project is scheduled to run until the end of 2019.
New Manufacturing Technologies for New Products
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
22.06.2017 | Life Sciences
22.06.2017 | Materials Sciences
22.06.2017 | Materials Sciences