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-delta has been studied by in situ Ce L-3 X-ray Absorption Near Edge Structure (XANES) spectroscopy during the reduction from room temperature to a 500 degrees C. The cerium ions start to reduce in the mixed oxide lattice at a temperature of 70 degrees C. 13% of Ce3+ has been detected in the studied sample during the reduction at a temperature of 70 degrees C. 26% of Ce4+ were reduced to Ce3+ at a temperature of 200 degrees C. No other changes were found in the Ce valence state up to the temperature of 500 degrees 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-delta is very similar to that of Ce0.875Pd0.125O2. The theoretical calculations using the Density Functional Theory method supported the experimental Ce L-3 XANES spectra. It was shown that the presence of Yb and Pd ions could enhance the formation of oxygen vacancies in cerium mixed oxides.

Automated summary

The presence of mixed-valence state Ce4+/Ce3+ in Ce0.7Yb0.2Pd0.1O2-delta was confirmed, and the reduction activity temperature of Ce was found to be significantly lower than previously reported, with Yb and Pd ions enhancing oxygen vacancy formation.