CO adsorption, activation, and oxidation on CeO₂(111)-supported Fe model catalyst surfaces

Elucidating the synergistic effect of Fe on CeO₂ is challenging in CO-related reactions but attractive owing to the improvement in the oxygen storage/release capacity of ceria with the addition of Fe. Here, using CeO₂(111)-supported Fe model catalysts, CO adsorption, activation, and oxidation on catalyst surfaces was carefully investigated using synchrotron radiation photoemission spectroscopy (SRPES), temperature-programmed desorption (TPD), and infrared reflection absorption spectroscopy (IRRAS). The precursor π-bonding state for CO dissociative adsorption has been identified through unusually low CO vibration frequencies and a low dissociation temperature on Fe/CeO₂(111) surfaces. CO is oxidized by dissociated atomic O followed by the Langmuir–Hinshelwood mechanism, whereas the lattice oxygen of CeO₂ exhibits low activity. The CO₂ yield displays a volcanic curve as a function of Fe coverage. On the 0.6 ML Fe/CeO₂ surface, weakly bound atomic O on Fe²⁺ results in the best catalytic activity. While on high Fe coverage surfaces, the CO₂ yield is limited due to the capture of atomic O by Fe⁰. Our results provide comprehensive insights into the adsorption, activation, and oxidation of CO on Fe/CeO₂ and identify the reaction mechanism, and the active site, which provides deeper insights into CO-related reaction mechanisms over CeO₂-supported Fe catalysts.