Raman Analysis of Mode Softening in Nanoparticle CeO2−δ and Au-CeO2−δ during CO Oxidation

Oxygen vacancy levels are monitored during the oxidation of CO by CeO2−δ nanorods and Au-CeO2−δ nanorods, nanocubes, and nanopolyhedra by using Raman scattering. The first-order CeO2 F2g peak near 460 cm–1 decreases when this reaction is fast (fast reduction and relatively slow reoxidation of the surface), because of the lattice expansion that occurs when Ce3+ replaces Ce4+ during oxygen vacancy creation. This shift correlates with reactivity for CO oxidation. Increases in the oxygen deficit δ as large as ∼0.04 are measured relative to conditions when the ceria is not reduced.