Probing the persistence of Ce3+ species on ceria during redox cycling by modulation‑excitation and resonant photoelectron spectroscopy (MES–RPES)

Luis Cardenas^a, Cyril Hachemi^a, Hadi Dib^b, Mourad Debbichi^c, Michael Badawi^d, Calley Eads^e^,^f, Maya Ibrahim^b, Stéphane Loridant^a, Jan Knudsen^e^,^f, Helena Kaper^b

^aIRCELYON, CNRS, Université Claude Bernard Lyon 1, France

^bSaint Gobain Recherche Provence, France

^cLaboratoire de la matière condensée et nanosciences, Université de Monastir, Tunisia

^dUniversité de Lorraine, CNRS, L2CM, France

^eDivision of Synchrotron Radiation Research, Department of Physics, Lund University, Sweden

^fMAX IV Laboratory, Lund University, Sweden

Proceedings of MATSUS Spring 2026 Conference (MATSUSSpring26)

G4 In situ/operando characterization of energy-related materials with synchrotron X-ray techniques

Barcelona, Spain, 2026 March 23rd - 27th

Organizers: Carlos Escudero and Juan Jesús Velasco Vélez

Oral, Luis Cardenas, presentation 719
Publication date: 15th December 2025

Many in situ, surface-sensitive studies assume that the most detectable surface species explains catalytic activity, overlooking fast, short‑lived species. Here, we combine modulation excitation (MES)[1] with resonant photoelectron spectroscopy (RPES)[2] to follow transient valence‑band signals during CO oxidation on ceria. Alternating O₂ and CO pulses every 40 seconds switches the surface between Ce⁴⁺ and Ce³⁺. RPES tracking of Ce 4f (Fig. 1), together with simultaneous O2 and CO mass spectrometry, shows Ce³⁺ forming under CO and vanishing under O₂ in repeatable cycles.
Varying gas ratios reveals that CO‑rich feeds (CO:O2 ≥ 1) yield only partial Ce³⁺ → Ce⁴⁺conversion (Fig 1(a)), while O₂‑rich pulses achieve complete reoxidation (Fig. 1(c)). This behavior reflects the temperature-dependent availability of Intermediate oxygen species: in pure O2, peroxo and OH coexist between 330–360 °C, while above 390 °C only OH remains stable.[3] Overall, controlled chemical modulation distinguishes active intermediates from spectators and connects ceria’s surface redox oscillations to catalytic turnover.

References:

[1] [1] Roger, M.; Artiglia, L.; Boucly, A.; Buttignol, F.; Agote-Arán, M.; Bokhoven, J. A. van; Kröcher, O.; Ferri, D. Improving Time-Resolution and Sensitivity of in Situ X-Ray Photoelectron Spectroscopy of a Powder Catalyst by Modulated Excitation. Chem. Sci. 2023, 14 (27), 7482–7491

[2] [2] Lykhach, Y.; Kozlov, S. M.; Skála, T.; Tovt, A.; Stetsovych, V.; Tsud, N.; Dvořák, F.; Johánek, V.; Neitzel, A.; Mysliveček, J.; Fabris, S.; Matolín, V.; Neyman, K. M.; Libuda, J. Counting Electrons on Supported Nanoparticles. Nat. Mater. 2016, 15 (3), 284–288

[3] [3] Hachemi, C.; Dib, H.; Debbichi, M.; Badawi, M.; Eads, C.; Ibrahim, M.; Loridant, S.; Knudsen, J.; Kaper, H.; Cardenas, L. Persistence of Ce3+ Species on the Surface of Ceria during Redox Cycling: A Modulated Chemical Excitation Investigation. Phys. Chem. Chem. Phys. 2025, 27 (22), 12069–12079

Acknowledgements:

We thank the following funding sources for this project: The LABEX iMUST of the University of Lyon (PINCELL: ANR-10-LABX-0064) and ANR-NACELL (Project-ANR-22-CE42-0011), created within the ‘‘Plan France 2030’’ set up by the French government and managed by the French National Research. This work was supported by Carnot MICA within the Photoacteur project

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