Preparation, characterisation and catalytic property of ultrafine Ce-La-Mn mixed oxides

摘要

Using cerium carbonate, lanthanum oxide and manganese nitrate as raw materials, ultrafine particles of Ce-La-Mn mixed oxides were prepared by the sol-gel method combined with supercritical drying technology. The prepared materials were characterised by thermo-gravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscope. The catalytic properties of ultrafine Ce-La-Mn mixed oxides were tested by the reaction '2CO+2NO=2CO_2+N_2'. The key aim was to examine the effect of supercritical fluid drying technology and Ce-doping on the crystal structure, morphology and catalytic activity of ultrafine Ce-La-Mn mixed oxides. The results show that at 260℃, Ce-La- Mn mixed oxides are brown loose flocculent powders with good dispersibility. The particles are spherical about 10nm in size. The main crystal components are CeO_2, MnO, La_5O_7NO_3 and La(OH)_2NO_3. After thermal treating at 850℃, Ce-La-Mn mixed oxides were made up of plenty of quasi-global grains smaller than 20 nm; the main crystal components of the Ce-La-Mn mixed oxides are LaMnO_(3+λ), La_2O_3 and CeO_2; heat treatment can enhance the crystallinity of the materials. Cerium-doped mixtures just exist as crystal CeO_2, which contributes to the crystallisation of Ce-La-Mn mixed oxides in the process of supercritical fluid drying at 260℃, enhancing the catalytic activity of ultrafine Ce-La-Mn mixed oxides which are thermal treated at 850℃.