Unusual Redox Behavior of Ceria and Its Interactionwith Hydrogen
2019
The
reaction between ceria and hydrogen has been subject to numerous
theoretical and experimental studies because of its importance as
a catalytic material. Here, we present dynamic and reversible evolution
of the cerium oxidation states observed through X-ray absorption spectroscopy
experiments in addition to the investigation of associated lattice
expansion and contraction through X-ray diffraction and PDF methods.
Employing a novel calculation of the temperature dependence of the
Gibbs free energy through consideration of the relationship between
the instantaneous thermal lattice expansion and the rate of change
of the cerium oxidation state, the unusual redox chemistry is reported
here. This unusual behavior is interpreted to be due to the formation
of a metastable cerium oxyhydride as suggested.
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