General and facile synthesis of ceria-based solid solution nanocrystals and their catalytic properties

Uniform Ce1−xZrxO2 (x=0.2–0.8) nanocrystals with ultra-small size were synthesized through a thermolysis process, facilitated by the initial formation of precursor (hydrated (Ce,Zr)-hydroxides) at low temperature. TEM, XRD, EDAX, and Raman spectra were employed to study the formation of the solid solutions with various Ce/Zr ratios. Ultraviolet–visible (UV–vis) spectra showed that the ratios of Ce3+ to Ce4+ in both surface and bulk for the as-prepared Ce1−xZrxO2 nanocrystals increased with the zirconium content x. The well-distributed Zr and Ce in the hydrated (Ce,Zr)-hydroxides before their thermolysis became the crucial factor for the structural homogeneity of the products. In addition, this strategy was extended to the synthesis of Ce1−xGdxO1−x/2, Ce1−xSmxO1−x/2, and Ce1−xSnxO2 solid solutions. Catalytic measurements indicated that the ceria-based catalysts were active for CO oxidation at temperatures beyond 250 °C and the sequence of catalytic activity was Ce0.5Zr0.5O2>Ce0.8Zr0.2O2>Ce0.2Zr0.8O2>Ce0.5Sm0.5O1.75.