Study of the formation of LaMO3 (M=Co, Mn) perovskites by propionates precursors: application to the catalytic destruction of chlorinated VOCs

LaMO3 (M=Co, Mn) have been obtained by a sol–gel-like method with propionic acid as solvent. The influence of the nature of the metallic source (metal, nitrate or chloride) on the gel formation has been studied by fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis ATD–ATG. After calcination, the obtained perovskites have been characterised by X-ray diffraction (XRD), FTIR, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) in order to investigate the influence of the preparation parameters on the final product. These mixed oxides have been used as catalyst for the destruction of chlorinated compounds. For each compound, the perovskite structure of LaCoO3 decomposes in the same manner as LaOCl and Co3O4. Under the same test conditions, the perovskite with Mn is not altered. The stability of the structure has been explained by the formation of an oxygen overstoichiometric phase (LaMnO3+δ) which is thermodynamically more resistant to chlorination than the stoichiometric LaMnO3. The catalytic behaviour of these oxides shows that two ways (hydrolysis and oxidation) are involved in the destruction of chlorinated hydrocarbons. The first one requires acidic sites and is less sensitive to the modification of the catalyst surface induced by chlorine than the second one requiring metallic oxidation sites.