Redox behavior of nanocrystalline Ce 1− xLu xO 2− x/2 mixed oxide obtained by microemulsion method

Abstract

Nanocrystalline Ce 1− x Lu x O 2− x/2 ( x = 0.17, 0.25, 0.5) mixed oxides with narrow size distribution (4–5 nm) were prepared by a water-in-oil (W/O) microemulsion method. Microstructure and reduction–reoxidation properties of the oxides were analyzed by HRTEM, STEM-EDX, XRD, H 2-TPR and TPO. The presence of Lu 3+ ion in the cation sublattice generates strain in the ceria lattice through the creation of crystal imperfections and oxygen vacancies and drastically affects redox properties of the system. All synthesized samples had fluorite structure of CeO 2 from XRD and all exhibited significant, low temperature reducibility (max. at 368 °C), persisting after repeated reduction and low temperature oxidation cycles at 500 °C. Oxidation treatment at higher temperature (950 °C) destroyed completely the low temperature reducibility of the mixed oxides, that could not be accounted for to particle growth. TPO data indicated that Ce 3+ species formed after reduction at 930 °C in the Ce 0.83Lu 0.17O 1.915 and Ce 0.75Lu 0.25O 1.875 samples were very sensitive to oxygen atmosphere even at room temperature. However, some Ce 3+ species formed in the Ce 0.5Lu 0.5O 1.75 sample were very stable in air. Additionally, the existence of biphasic region (F + C) was also unequivocally detected by HRTEM and TPO method in nanocrystalline Ce 0.5Lu 0.5O 1.75 after oxidation treatment at 950 °C.