High-Temperature Growth of CeO on Au(111) and Behavior under Reducing and Oxidizing Conditions

Inverse oxide-metal model catalysts can show superior activity and selectivity compared with the traditional supported metal-oxide architecture, commonly attributed to the synergistic overlayer-support interaction. We have investigated the growth and redox properties of ceria nanoislands grown on Au(111) between 700 and 890 °C, which yields the CeO₂-Au(111) model catalyst system. We have observed a distinct correlation between deposition temperature, structural order, and oxide composition through low-energy electron microscopy, low-energy electron diffraction, intensity-voltage curves, and X-ray absorption spectroscopy. Improved structural order and thermal stability of the oxide have been achieved by increasing the oxygen chemical potential at the substrate surface using reactive oxygen (O/O₂) instead of molecular O₂ during growth. In situ characterization under reducing (H₂) and oxidizing atmospheres (O₂, CO₂) indicates an irreversible loss of structural order and redox activity at high reduction temperatures, while moderate temperatures result in partial decomposition of the ceria nanoislands (Ce³⁺/Ce⁴⁺) to metallic cerium (Ce⁰). The weak interaction between Au(111) and CeO would facilitate its reduction to the Ce⁰ metallic state, especially considering the comparatively strong interaction between Ce⁰ and Au⁰. Besides, the higher reactivity of atomic oxygen promotes a stronger interaction between the gold and oxide islands during the nucleation process, explaining the improved stability. Thus, we propose that by driving the nucleation and growth of the ceria/Au system in a highly oxidizing regime, novel chemical properties can be obtained.