The low temperature reducibility of Ce4+ ions in Ce0.7Yb0.2Pd0.1O2-δ: in situ XANES study

Cerium mixed oxides are interesting materials for the oxygen storage capacity due to the Ce ability to valence state changes and oxygen vacancy formation. The mixed-valence state Ce4+/Ce3+ in Ce0.7Yb0.2Pd0.1O2-δ has been studied by in situ Ce L3 X-ray Absorption Near Edge Structure (XANES) spectroscopy during the reduction from room temperature to a 500 °C. The cerium ions start to reduce in the mixed oxide lattice at a temperature of 70 °C. 13% of Ce3+ has been detected in the studied sample during the reduction at a temperature of 70 °C. 26% of Ce4+ were reduced to Ce3+ at a temperature of 200 °C. No other changes were found in the Ce valence state up to the temperature of 500 °C. The most interesting result is that the reduction of Ce4+ to Ce3+ starts clearly before the reduction of the noble metal. The redox activity temperature range of Ce in mixed oxides is significantly lower than reported by other authors.