Ce–Zr-Sm ternary oxides synthesized via a template free urea-hydrothermal method

Abstract

Nano-crystalline Ce0.9Zr0.1-xSmxO2-δ (0 ≤ x ≤ 0.10) mixed oxides were synthesized for the first time by a urea-hydrothermal method without the use of template or structure directing agents. The use of a high molar ratio of urea to metal cations and temperature reaction ensures the formation of a single-phase homogeneous ternary solid solution. The (NH4)2Ce(NO3)6 precursor, in a greater proportion, together with urea acts as a structure directing agent towards the completion of a self-assembly shuttle to dumbbells to sphere sequence. The analysis of the obtained morphologies has demonstrated that the physicochemical nature of the doping precursor in solution has a strong influence on the final morphology without losing morphological control. Thus, the ZrO(NO3)2 precursor favors the formation of cauliflower-type particles whereas Sm(NO3)3 favors the formation of spheres. As a result, the morphology of the samples evolves from cauliflowers to spheres as Sm content increases in the mixed oxides, with a great effect on the high specific surface area (80–115 m2.g−1) and total pore volume (0.109–0.315 cm3.g−1) obtained in all cases. Solids reduce in three stages reaching high reduction percentages (≈50%).