Electronic and Geometric Structure of Ce3+Forming Under Reducing Conditions in Shaped Ceria Nanoparticles Promoted by Platinum

The structure of Ce 3+, which is responsible for the low-temperature oxygen storage capacity of ceria, was determined by high-energy-resolution fluorescence detected X-ray absorption spectroscopy at the Ce L 3 and L 1 edges. Well-defined ceria nanoparticles (rods, truncated octahedra, and cubes) were synthesized hydrothermally and promoted by platinum nanoparticles. The electronic structure of Ce 3+ does not depend significantly on the nature of the exposed crystallographic planes of CeO 2 particles; it does, however, differ from the electronic structure of known stable compounds containing Ce 3+ ions, such as CeAlO 3, Ce(NO 3 ) 3 ·6H 2 O, and Ce 2 Zr 2 O 7 . Theoretical simulation of Ce L 1 and L 3 X-ray absorption spectra, quantitative analysis of the oxygen storage capacity, and X-ray diffraction data suggest that Ce 3+ ions form both at the surface and in the near-surface layer. Surface and bulk Ce 3+ ions are characterized by elongated Ce–O distances in the first coordination shell and almost the same Ce–Ce distances in the second coordination shell with respect to Ce 4+ in stoichiometric CeO 2 . Ce 3+ ions on the surface of the nanoparticles surface may have a smaller number of oxygen neighbors (as low as six), while in the near-surface layer they tend to have an 8-fold coordination, thus producing oxygen deficit structures similar to Ce 11 O 20 .