Urea-Based Hydrothermally Derived Homogeneous Nanostructured Ce_(1-x)Zr_xO_2 (x = 0-0.8) Solid Solutions:A Strong Correlation between Oxygen Storage Capacity and Lattice Strain

摘要

Ce_(1-x)Zr_xO_2 (x = 0-0.8) nanoparticulate powders were prepared via a mild urea hydrolysis based hydrothermal method through homogeneous nucleation at 413 K followed by calcination at 773 or 1173 K.X-ray fluorescence (XRF) and energy-dispersive X-ray analysis (EDAX) measurements testify to the good stoichiometric homogeneity of Ce and Zr cations in the as-obtained Ce_(1-x)Zr_xO_2 products.X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible (UV-vis) spectra exhibit that both surface and bulk ratios of Ce~(3+) to Ce~(4+) for the as-prepared Ce_(1-x)Zr_xO_2 nanocrystals increased with the zirconium content x.Powder X-ray diffraction (PXRD) patterns and Raman spectra demonstrate that the present Ce_(1-x)Zr_xO_2 samples were single-phase solid solutions with good structural homogeneity and high thermal stability up to 1273 K,and those with x = 0.4-0.6 retained a pseudocubic structure (t" phase) due to the small crystallite size effect.Transmission electron microscopy (TEM) micrographs reveal that the as-prepared CeO_2-ZrO_2 nanocrystals were highly crystallized with narrow size distribution.Nitrogen adsorption measurements show that the BET specific surface areas of the Ce_(1-x)Zr_xO_2 powders were improved by the incorporation of ZrO_2.The PXRD data and high-resolution TEM (HRTEM) images illuminate that the as-prepared and as-calcined Ce_(1-x)Zr_xO_2 (x = 0.4-0.6) powders kept a rather high strain level in the crystal lattice.The lattice strains in our Ce_(1-x)Zr_xO_2 catalysts show a linear relationship with their oxygen storage capacity (OSC) values.This linear correlation is explained on the basis of qualitative structural and defective analysis,and might find use in the screening and design of better-performing three-way catalysts (TWCs).The highest CO-OSC values of the studied CeO_2-ZrO_2 catalysts appeared for Ce_(0.5)Zr_(0.5)O_2 (543 mumol of CO g~(-1) at 773 K and 628 mumol of CO g~(-1) at 973 K).