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Researchers use LCLS to get real-time view of chemical reaction; important insight into how catalysts work
15 March 2013
An international team of researchers has used the ultrafast, ultrabright X-ray pulses of the Linac Coherent Light Source (LCLS) at the US Department of Energy’s (DOE) SLAC National Accelerator Laboratory (earlier post) to gain unprecedented views of a catalyst in action, an important step in the effort to develop cleaner and more efficient energy sources. A paper on their work is published in the journal Science.
The scientists used LCLS, together with computerized simulations, to probe the electronic structure of CO molecules as their chemisorption state on a ruthenium catalyst sample changed upon exciting the substrate. The study revealed surprising details of a short-lived early state in the chemical reaction, offering important clues about how catalysts work and launching a new era in probing surface chemistry as it happens.
Catalysts, which can speed up chemical reactions and make them more efficient and effective, are essential to most industrial processes and to the production of many chemicals. Catalytic converters in cars, for example, reduce emissions by converting exhaust to less toxic compounds.
Understanding how catalysts work, at ultrafast time scales and with molecular precision, is essential to producing new, lower-cost synthetic fuels and alternative energy sources that reduce pollution, said said Anders Nilsson, deputy director for the Stanford and SLAC SUNCAT Center for Interface Science and Catalysis and a leading author in the research.
|How LCLS views surface chemistry (Credit: Hirohito Ogasawara / SLAC National Accelerator Laboratory) Click to enlarge.|
In the LCLS experiment, the scientists shot the crystal’s surface with a pulse from a conventional laser, which caused carbon monoxide molecules to begin to break away. They then probed this state of the reaction using X-ray laser pulses, and observed that the molecules were temporarily trapped in a near-gas state and still interacting with the catalyst.
“We never expected to see this state,” Nilsson said. “It was a surprise.”
Not only was the experiment the first to confirm the details of this early stage of the reaction, it also found an unexpectedly high share of molecules trapped in this state for far longer than what was anticipated, raising new questions about the atomic-scale interplay of chemicals that will be explored in future research.
Some of the early stages of a chemical reaction are so rapid that they could not be observed until the creation of free-electron lasers such as LCLS, said Jens Nørskov, director of SUNCAT. Future experiments at LCLS will examine more complex reactions and materials, Nilsson said.
Important preliminary research was conducted at SLAC’s Stanford Synchrotron Radiation Lightsource (SSRL), and this direct coupling of research at SLAC’s synchrotron and X-ray laser proved essential, said Hirohito Ogasawara, a staff scientist at SSRL.
Collaborators participating in the research were from SLAC; Stanford University; University of Hamburg, Center for Free-Electron Laser Science, Helmholtz-Zentrum Berlin for Materials and Energy, University of Potsdam and Fritz-Haber Institute of the Max Planck Society in Germany; Stockholm University in Sweden; and the Technical University of Denmark. This work was supported by DOE’s Office of Science, the Swedish National Research Council, the Danish Center for Scientific Computing, the Volkswagen Foundation and the Lundbeck Foundation.
SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the US Department of Energy Office of Science. LCLS and SSRL are supported by the DOE’s Office of Science.
M. Dell’Angela, T. Anniyev, M. Beye, R. Coffee, A. Föhlisch, J. Gladh, T. Katayama, S. Kaya, O. Krupin, J. LaRue, A. Møgelhøj, D. Nordlund, J. K. Nørskov, H. Öberg, H. Ogasawara, H. Öström, L. G. M. Pettersson, W. F. Schlotter, J. A. Sellberg, F. Sorgenfrei, J. J. Turner, M. Wolf, W. Wurth, and A. Nilsson (2013) Real-Time Observation of Surface Bond Breaking with an X-ray Laser. Science 339 (6125), 1302-1305. doi: 10.1126/science.1231711
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