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要旨

CoFe₂O₄ nanoparticles (NPs) were synthesized by using a colloidal one-pot synthesis method based on the decomposition of metal acetylacetonates in the presence of oleyl amine. The characterization by X-ray diffraction, transmission electron microscopy and N₂ physisorption revealed non-porous spinel phase CoFe₂O₄ NPs with an average particle size of 4 nm. The unsupported metal oxide NPs were applied in the selective oxidation of 2-propanol in a continuously operated fixed-bed reactor under quasi steady-state conditions using a heating rate of 0.5 k min^-1. 2-Propanol was found to be oxidatively dehydrogenated over CoFe₂O₄ yielding acetone and H₂O with high selectivity. Only to a minor extent dehydration to propene and total oxidation to CO₂ was observed at higher temperatures. The detected low-temperature reaction pathway with maxima at 430 and 510 K was inhibited after the initial 2-propanol oxidation up to 573 K, but an oxidative treatment in O₂ or N₂O atmosphere led to full regeneration. No correlation between the desorbing amount or the surface oxygen species investigated by O₂ temperature-programmed desorption experiments and the low-temperature activity was observed. The amounts of evolving CO₂ during the TPO experiments indicate deactivation due to formation of carbonaceous species. Inhibition experiments with pre-adsorbed reaction intermediates and infrared spectroscopy identified acetate species as reversible poison, whereas carbonates are rather spectators. In addition, carbon deposition was detected by X-ray photoelectron spectroscopy, which also revealed a minor influence of cobalt reduction during the deactivation process as confirmed by X-ray absorption spectroscopy studies.