Urea-based hydrothermally derived homogeneous nanostructured Ce1-xZrxO2 (x=0-0.8) solid solutions:: A strong correlation between oxygen storage capacity and lattice strain

Ce1-xZrxO2 (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 Ce1-xZrxO2 products. X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible (UV-vis) spectra exhibit that both surface and bulk ratios of Ce3+ to Ce4+ for the as-prepared Ce1-xZrxO2 nanocrystals increased with the zirconium content x. Powder X-ray diffraction (PXRD) patterns and Raman spectra demonstrate that the present Ce1-xZrxO2 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 CeO2-ZrO2 nanocrystals were highly crystallized with narrow size distribution. Nitrogen adsorption measurements show that the BET specific surface areas of the Ce1-xZrxO2 powders were improved by the incorporation of ZrO2. The PXRD data and high-resolution TEM (HRTEM) images illuminate that the as-prepared and as-calcined Ce1-xZrxO2 (x = 0.4-0.6) powders kept a rather high strain level in the crystal lattice. The lattice strains in our Ce1-xZrxO2 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 CeO2-ZrO2 catalysts appeared for Ce0.5Zr0.5O2 (543 mumol of CO g(-1) at 773 K and 628 mumol of CO g(-1) at 973 K).