Materials Chemistry and Physics, Vol.229, 49-55, 2019
New doubly doped cerium oxide Ce1-x-yYbyPdxO2-delta: 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-delta (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 OFT 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-delta and Ce1-x-yYbyPdO2-delta. 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 EXAES spectra for Ce(1-x-Y)b(y)Pd(x)O(2-delta) indicate a partial reduction of palladium at 200 degrees C and almost complete (90%) at 500 degrees C in hydrogen. The presence of ytterbium in Ce1-x-yYbyPdxO2-delta prevents the formation of metallic particles in reducing atmosphere (up to 500 degrees C) and strongly inhibits crystal growth of the mixed oxide.