Redox behavior of nanocrystalline Ce1−xLuxO2−x/2 mixed oxide obtained by microemulsion method
Nanocrystalline Ce1−xLuxO2−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, H2-TPR and TPO. The presence of Lu3+ 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 CeO2 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 Ce3+ species formed after reduction at 930 °C in the Ce0.83Lu0.17O1.915 and Ce0.75Lu0.25O1.875 samples were very sensitive to oxygen atmosphere even at room temperature. However, some Ce3+ species formed in the Ce0.5Lu0.5O1.75 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 Ce0.5Lu0.5O1.75 after oxidation treatment at 950 °C.
Graphical abstractMicrostructure and reduction–reoxidation properties of nanocrystalline (∼5 nm) Ce1−xLuxO2−x/2 (x = 0.17, 0.25, 0.5) mixed oxides prepared by a microemulsion method was studied. The oxides exhibited significant, low temperature reducibility (max. at 368 °C), persisting after repeated reduction and low temperature oxidation cycles at 500 °C. Oxidation at high temperature (950 °C) destroyed the low temperature reducibility due to nanoscale phase separation.Figure optionsDownload full-size imageDownload as PowerPoint slide
Journal: Applied Catalysis A: General - Volume 368, Issues 1–2, 31 October 2009, Pages 71–78