Persistence of Ce³⁺ species on the surface of ceria during redox cycling: a modulated chemical excitation investigation

Summary

<i>Operando</i> resonant photoelectron spectroscopy (RPES) combined with modulated chemical excitation revealed the dynamic evolution of Ce³⁺/Ce⁴⁺ redox states at the surface of CeO₂ during the CO oxidation reaction. Using alternating CO and O₂ pulses as chemically modulated signals, we monitored the surface states in the valence band region, unveiling the evolution of electronic structure during the catalytic process. The analysis with different gas flow ratios revealed that under CO-rich conditions (CO : O₂ ≥ 1), only partial conversion from Ce³⁺ to Ce⁴⁺ occurred. In contrast, complete Ce³⁺ to Ce⁴⁺ conversion was achieved when pulsing O₂ into O₂-rich environments. Furt