Reactive Surface Structure Observed In Real Time

To understand exactly how a catalytic material works or a surface corrodes, it helps to understand their structures and how they change during reactions. Typical techniques that enable structure determination with high resolution also require ultrahigh vacuum, however, making it difficult to watch materials change in real time under industrially relevant conditions. A group led by Johan Gustafson of Sweden’s Lund University has now demonstrated use of high-energy synchrotron X-rays and a larger-than-standard detector to study a palladium surface as it catalyzes oxidation of carbon monoxide to carbon dioxide (Science 2014, DOI: 10.1126/science.1246834). The approach does not require a vacuum and eliminates the need to move a detector around the sample to catch diffracted X-rays—the higher energy X-rays diffract at a smaller angle and can be caught in one place by the larger detector. Using a flow chamber, Gustafson collected diffraction data at intervals of 0.5 seconds as the team exposed the Pd to CO and O₂. At high O₂ concentrations, the researchers observed a PdO film grow over the surface as CO₂ production commenced. The approach should also work to study buried structures or those at solid-liquid interfaces, the researchers say.