Catalysis by shapely nanocrystals of the Ce1−xYbxO2−x/2 mixed oxides — Synthesis and phase stability

Abstract This work presents results of studies on the shape and structural stability of the crystalline ceria-based Ce 1−x Yb x O 2−(x/2) mixed oxides with increasing Yb content (x = 0–0.50). The cube-like, and octahedral nanocrystals of the oxides were synthesized by the hydrothermal method using two different heating methods of the stainless steel Teflon-lined autoclaves — conventional (the heating mantle) and microwave assisted one. It was observed that the predetermined shape of the investigated samples was kept up to x = ~0.2. Above this value, the co-product of synthesis as a rice-like Yb-phosphates have been observed near to octahedron-like Ce 1−x Yb x O 2−(x/2) mixed oxides. In case of cube-like samples, for concentrations of Yb-ions over 20–30%, the shape of crystals starts to be round. Moreover, weaker incorporation of the Yb 3+ -ions into the CeO 2 structure was noticed in case octahedron-like samples than cube-like ones. Additionally, it was found that the mean particle sizes of the octahedral ceria based mixed oxides prepared by the conventional hydrothermal method were larger than the same materials prepared by the microwave assisted method. Thanks to enhanced reducibility at low temperatures and good thermal stability of Ce 1−x Yb x O 2−(x/2) , the investigated oxides are good candidates for catalysts of soot oxidation. For the octahedron-like Ce 0.9 Yb 0.1 O 1.95 the temperature of half oxidation (T 50%  = 423 °C) was 154 °C lower than that for non-catalysed oxidation (T 50%  = 577 °C). On the other hand, the most stable catalysts were cube-like oxides, both pure and doped ceria (CeO 2 — T Icycle 50%  = 438 °C; T IIcycle 50%  = 454 °C and Ce 0.9 Yb 0.1 O 1.95 — T Icycle 50%  = 435 °C; T IIcycle 50%  = 453 °C).