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

Abstract

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 = 2CO2 + N2’. 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°C, Ce–La–Mn mixed oxides are brown loose flocculent powders with good dispersibility. The particles are spherical about 10 nm in size. The main crystal components are CeO2, MnO, La5O7NO3 and La(OH)2NO3. After thermal treating at 850°C, 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 LaMnO3+ λ , La2O3 and CeO2; heat treatment can enhance the crystallinity of the materials. Cerium-doped mixtures just exist as crystal CeO2, which contributes to the crystallisation of Ce–La–Mn mixed oxides in the process of supercritical fluid drying at 260°C, enhancing the catalytic activity of ultrafine Ce–La–Mn mixed oxides which are thermal treated at 850°C.