Operando Monitoring of Homolytic Cleavage of H2 into Surface Hydrides on Defective Cerium Dioxide Nanoparticles

The use of ceria as catalyst in hydrogenation reactions is a recent trend. While some studies focused on well-defined shapes, others emphasized the interest of defective structures. Overall, there is a need to characterize the surface reactivity vs. H2 for a number of textures, while preserving the features of the materials. It is key to assess the formation of surface hydride through homolytic H2 splitting, at cerium sites rather than at the oxygen one. We designed a low-temperature synthetic route for CeO2 nanorods. We employed near-ambient-pressure X-ray photoelectron spectroscopy to monitor the cerium surface oxidation state and the presence of hydroxyls during the initial annealing of the nanopowder, followed by exposure to a moderate pressure of H2. We demonstrate that H2 homolytic splitting at cerium sites is the main activation process at 100 °C, leading to the oxidation of 30% of the surface cerium atoms, while the H2 splitting at oxygen sites was absent. The surface hydride species were unstable at 250 °C, H2 was released, and cerium reduced back to Ce3+. Overall, we report here that CeO2 nanorods show an interesting surface reactivity for future application in hydrogenation, and we expose a straight operando methodology to delineate suitable temperatures.