Abstract
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.The total density of states (DOS) of Ce0.7Yb0.2Pd0.1O2-δ is very similar to that of Ce0.875Pd0.125O2. The theoretical calculations using the Density Functional Theory method supported the experimental Ce L3 XANES spectra. It was shown that the presence of Yb and Pd ions could enhance the formation of oxygen vacancies in cerium mixed oxides.
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