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

摘要

Trivalent rare-earth (RE = La, Pr, Nd, Y)-doped CexZr1-xO2 (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 CeO2-ZrO2 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 CexZr1-x-yREyO2-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 CeO2-ZrO2-RE2O3 solid solutions after calcination at 1000 C for 100 h. The aliovalent substitution of the RE3+ ion for the Ce4+ or Zr4+ 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 CeO2-ZrO2 system. The reducibility of the as-calcined CexZr1-x-yREyO2-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 Ce0.5Zr0.42Nd0.08O2-z in 558 mol CO g-1 at 700 C, while the undoped samples gave a value of less than 460 mol CO g-1.