Credit: Oak Ridge National Laboratory, U.S. Dept. of Energy; illustrator Adam Malin
Neutrons probed two mechanisms proposed to explain what happens when hydrogen gas flows over a cerium oxide (CeO2) catalyst that has been heated in an experimental chamber to different temperatures to change its oxidation state. The first mechanism suggests hydrogen (H) atoms each associate with only oxygen (O) atoms to produce only OH species on the surface. The ORNL-led study instead provides evidence for the second mechanism, in which one H atom associates with an O atom to make OH and the other H associates with cerium (Ce) to make CeH—a hydride that may serve as a source of H for industrially important hydrogenation reactions. Color code: hydrogen, blue; oxygen, red; surface Ce, light yellow; bulk Ce, green.