Elucidating the Nature of the Active Phase in Copper/Ceria Catalysts for CO Oxidation

The active phase responsible for low-temperature CO oxidation in nanoparticulate CuO/CeO2 catalysts was identified as surface-substituted CuyCe1-yO2-x. Contrary to previous studies, our measurements on a library of well-defined CuO/CeO2 catalysts have proven that the CuO phase is a spectator species, whereas the surface-substituted CuyCe1-yO2-x phase is active for CO oxidation. Using in situ X-ray absorption spectroscopy, we found that the copper ions in CuyCe1-yO2-x remain at high oxidation states (Cu3+ and Cu2+) under oxygen-rich catalytic conditions without any evidence for Cu+. Artificial neural network potential Monte Carlo simulations suggest that Cu3+ and Cu2+ preferentially segregate to the {100} surface of the CuyCe1-yO2-x nanoparticle, which is supported by aberration-corrected electron microscopy measurements. These results pave the way for understanding, at the atomic level, the mechanisms and descriptors pertinent for CO oxidation on these materials and hence the rational design of next-generation catalysts.