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

Abstract

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_x 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.