PARTIAL OXIDATION OF METHANE TOSYNGAS BY LACOO3 OXIDATIVE CATALYST

摘要

The LaCoO3 perovskites were prepared by modified wet powder dispersion (LaCoO3-wd) and co-precipitation (LaCoO3-cp) methods. Both prepared samples were characterized by means of x-ray diffraction (XRD), BET surface area, scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and x-ray adsorption near edge spectroscopy (XANES). XRD results suggested that the main crystalline phase of all prepared LaCoO3 was a rhombohedral perovskite structure. The particle size of LaCoO3 was calculated by Scherrer's equation giving the size of 28 nm from both modified wet powder dispersion and co-precipitation methods. From BET surface area analysis, the surface areas of LaCoO3 were 11.75 and 11.69 m~2g~(-1) for modified wet powder dispersion and co-precipitation methods, respectively. Moreover, SEM and TEM images showed the difference in morphology which strongly depended on the preparation methods. From XPS, the ratio of adsorbed and lattice oxygen in the LaCoO3-wd was 5.51 and 4.11 for LaCoO3-cp catalyst. From XANES results, the peak edge energy for LaCoO3-cp was 7720.8 eV, giving an average Co oxidation state close to 2. For the LaCoO3-wd peak edge energy of 7722.0 eV, an average Co oxidation was between 2 and 3. The reactivity of the LaCoO3 perovskites with respect to partial oxidation of methane (POM) was studied. Both CH4 conversion and CO yield were found to increase at the high reaction temperature. For POM testing, LaCoO3 from the modified wet powder dispersion method gave high CH4 conversion of 90% and the H2 yield of 1.15% compared with 78-85% CH4 conversion and 0.9% H2 yield from co-precipitation method at 700-900°C. The LaCoO3-wd and LaCoO3-cp catalysts showed the close POM catalytic activity. The modified wet powder dispersion could be an alternative method to synthesize LaCoO3.