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O: Fachverband Oberflächenphysik
O 63: Oxides and Insulator Surfaces: Adsorption and Reaction of Small Molecules II
O 63.5: Talk
Wednesday, March 19, 2025, 11:30–11:45, H25
Tracking the redox cycle of CeO2 by Infrared spectroscopy via a titration of the defect states by O2 adsorption. — •Lachlan Caulfield, Eric Sauter, Hicham Idriss, and Christof Wöll — Karlsruhe Institute of Technology
CeO2 is probably the most stable reducible metal oxide known. It is the main component of automobile three-way catalysts and is the chief prototype for the thermochemical water splitting to H2 and O2 reaction as well as for CO2 thermal reduction to CO. This is largely due to the relative stability of the Ce4f1 electron formed upon the removal of surface oxygen atoms during the reduction process. While these are commonly studied by photoelectron spectroscopy (XPS Ce3d or UPS Ce4f), less attention in general has been given to the Ce3+ (2F5/2 to 2F7/2) spin orbit transition of this process that appears in infrared spectroscopy at ca. 2150 cm−1. In this work we have monitored the formation of these transition on reduced polycrystalline CeO2 exposed to molecular O2 as a function of temperature using the DRIFT technique. Results have shown that there is a linear relationship between the disappearance of the observed electronic transition at ca. 2130-2160 cm−1 and the IR signal of the superoxo (O2−). species upon exposure of the reduced surface to different partial pressures of O2. Moreover, it was found that the oxidation process is irreversible: the spin-orbit transition signal does not recover upon the removal of adsorbed oxygen species. Work in progress to track the catalytic activity of these adsorbed O2 species and spin-orbit transition by probe molecules suitable for the redox cycle.
Keywords: Oxygen; Activation; Infrared; Ceria; Defects