X-Ray Pulses Expose Surface Reaction | Chemical & Engineering News
Volume 93 Issue 7 | p. 27 | Concentrates
Issue Date: February 16, 2015

X-Ray Pulses Expose Surface Reaction

Technique illuminates steps in a catalytic mechanism
Department: Science & Technology
News Channels: Materials SCENE, Analytical SCENE, Organic SCENE
Keywords: heterogeneous catalyst, oxidation, transition state

Femtosecond X-ray laser pulses can reveal new details of the mechanisms of surface-catalyzed reactions, reports an international team of researchers using the X-ray free-electron laser at SLAC National Accelerator Laboratory’s Linac Coherent Light Source (Science 2015, DOI: 10.1126/science.1261747). The method probes how electronic structure evolves in bimolecular interactions, resolving events that happen within hundreds of femtoseconds. The experiments were led by Anders Nilsson of SLAC and Stockholm University and Henrik Öström and Lars Pettersson of Stockholm University. The scientists studied carbon monoxide oxidation on a ruthenium surface. They used a so-called pump-probe approach, applying a 400-nm laser as the “pump” to excite the molecules, then X-ray pulses as the “probe” to generate X-ray absorption spectra of the reactants CO and O as they form the product CO2. Coupling the experimental data with theoretical modeling, the researchers suggest that the reactants go through a first transition state in which the reactants reorient on the surface and come together to form a long OC—O bond. The species then goes through a second transition state that involves a bent CO2 molecule with a shorter, but still elongated, OC–O bond.

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During CO oxidation on a ruthenium surface, the reactants go through two transition states before finally forming CO2, a study indicates (C = green, O = red, Ru = blue).
Credit: Adapted from Science
Models of CO, O, and CO2 on a ruthenium surface (C in green, O in red, Ru in blue).
 
During CO oxidation on a ruthenium surface, the reactants go through two transition states before finally forming CO2, a study indicates (C = green, O = red, Ru = blue).
Credit: Adapted from Science
 
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