Aqueous co-precipitation of Pd-doped cerium oxide nanoparticles: chemistry, structure, and particle growth

Nanoparticles of palladium-doped cerium oxide (Pd–CeO2) have been prepared by aqueous co-precipitation resulting in a single phase cubic structure after calcination according to X-ray diffraction (XRD). Inhomogeneous strain, calculated using the Williamson–Hall method, was found to increase with palladium content, and the lattice contracts slightly, relative to nano-cerium oxide, as palladium content is increased. Moreover, high resolution transmission electron microscopy reveals some instances of defective microstructure. These factors combined imply that palladium is in solid solution with CeO2 in these nanoparticles, but palladium (II) oxide (PdO) peaks in the Raman spectra indicate that solid solution formation is partial and that highly dispersed PdO is present as well as the solid solution. Nevertheless, the addition of palladium to the CeO2 lattice inhibits the growth of the 6% Pd–CeO2 particles compared to pure CeO2 between 600 and 850 C. Activation energies for grain growth of 54 ± 7 and 79 ± 8 kJ/mol were determined for 6% Pd–CeO2 and pure CeO2, respectively, along with pre-exponential Arrhenius factors of 10 for the doped sample and 600 for pure cerium oxide. Abbreviations XRD X-ray diffraction TWC Three-way catalyst Ceria Cerium oxide Zirconia Zirconium oxide PGM Platinum group metals HMT Hexamethylenetetramine ICP–OES Ion-coupled plasma/optical emission spectrometry FWHM Full-width at half-maximum CCD Charge coupled device TEM Transmission electron microscopy HRTEM High resolution transmission electron microscopy BNL Brookhaven National Laboratory XANES X-ray absorption near edge spectroscopy I.C.D.D. International Centre for Diffraction Data Ea Activation energy