Enhanced Thermal Stability and Oxygen Storage Capacity for CexZr1-xO2 (x = 0.4−0.6) Solid Solutions by Hydrothermally Homogenous Doping of Trivalent Rare Earths

Trivalent rare-earth (RE = La, Pr, Nd, Y)-doped Ce x Zr 1- x O 2 ( x = 0.4−0.6) solid solutions were synthesized via a urea hydrolysis-based hydrothermal method, followed by calcination at 1000 °C for 100 h. The X-ray absorption near-edge structure (XANES) tests for the Ce LIII edge determine that the chemical valence of the Ce atom in either undoped or RE-doped CeO 2 −ZrO 2 samples was mainly +4. The measurements of X-ray fluorescence (XRF) and energy-filtered transmission electron microscopy (EFTEM) testify to the good compositional homogeneity for Ce, Zr, and RE atoms in both bulk and microdomain of the as-calcined Ce x Zr 1- x - y RE y O 2- z ( x = 0.4−0.6, y = 0−0.16, and z is the number of oxygen vacancy) samples. The characterizations with X-ray diffraction (XRD) and vis-Raman demonstrate the high structural homogeneity for ternary CeO 2 −ZrO 2 −RE 2 O 3 solid solutions after calcination at 1000 °C for 100 h. The aliovalent substitution of the RE 3+ ion for the Ce 4+ or Zr 4+ ion has been concluded to stabilize the pseudo cubic t ‘ ‘ -structure, to improve the surface area and to enhance the oxygen storage capacity (OSC) for the binary CeO 2 −ZrO 2 system. The reducibility of the as-calcined Ce x Zr 1- x - y RE y O 2− z by CO seems dependent upon the nature and concentration of the RE dopant. The highest CO−OSC value obtained in this work appeared for Ce 0.5 Zr 0.42 Nd 0.08 O 2- z in 558 μmol CO g -1 at 700 °C, while the undoped samples gave a value of less than 460 μmol CO g -1 .