Vibrational fingerprint of the catalytically-active FeO2-x iron oxide phase on Pt(1 1 1)

We report here on the oxidation of monolayer FeO islands on Pt(1 1 1) into the highly-reactive FeO phase by high-temperature oxidation under Ultra High Vacuum (UHV) conditions. The chemical composition and characteristic phonon modes of both FeO and FeO films were investigated by X-ray photoemission Spectroscopy (XPS) and High Resolution Electron Energy Loss Spectroscopy (HREELS). The reactivity and thermal stability of the "oxygen-rich" FeO phase were studied with respect to the CO oxidation reaction at 450 K and to annealing in UHV at 563 K, respectively. By performing repeated oxidation/reduction cycles, we have identified the vibrational mode at 76 meV as the unique signature of the FeO phase and confirmed the already reported ability of CO to reduce such oxide at 450 K. The latter process is not fully reversible, suggesting a modification of the active sites upon CO adsorption.