New doubly doped cerium oxide Ce1-x-yYbyPdxO2-δ: The effect of ytterbium doping on stabilization of reduced palladium species on doped ceria oxide

The doubly and mono doped nanocrystalline mixed oxides Ce1-x-yYbyPdxO2-δ (y up to 0.4, x up to 0.2) were synthesized with the reversed microemulsion method. The morphology, microstructure and composition of the samples were investigated by TEM, EDS, XRD, XAFS, and DFT calculations of XANES spectra. The main aim of the study was the determination of the influence of an additional ytterbium content on structural and electronic properties of the Pd-doped ceria mixed oxide, i.e., the comparative discussion of the results obtained for Ce1-xPdxO2-δ and Ce1-x-yYbyPdxO2-δ. All samples were homogeneous fluorite-type nanocrystallites with very small size (3–5 nm). Reducibility studies revealed strong hydrogen consumption in these systems at low temperatures without any changes of their structure. The XANES and EXAFS spectra for Ce1-x-yYbyPdxO2-δ indicate a partial reduction of palladium at 200 °C and almost complete (90%) at 500 °C in hydrogen. The presence of ytterbium in Ce1-x-yYbyPdxO2-δ prevents the formation of metallic particles in reducing atmosphere (up to 500 °C) and strongly inhibits crystal growth of the mixed oxide.