Perovskite catalysts for the catalytic flameless combustion of methane - Preparation by flame-hydrolysis and characterisation by TPD-TPR-MS and EPR

A new method was employed for the preparation of a set of lanthanum cobalti tes of general formula La1-xMxCoO3+delta with M=Ce, Eu and x=0O, 0.05, 0.1, 0.2. All the samples thus prepared were nanostructured, thermally very sta ble and characterised by highly crystalline perovskite-like structure and h igh surface area. Their activity as catalysts for the catalytic flameless c ombustion (CFC) of methane was by ca. one order of magnitude higher than th at of their analogues, prepared through the usual calcination-milling (CM) procedure. Adsorption of oxygen was accompanied by formation of paramagneti c species. Desorption of preadsorbed oxygen was dependent on the nature of the doping element and on the value of the stoichiometric coefficient x of their formula. A correlation between the temperature of the maximal rate of oxygen release and catalytic activity was found. The following scale of ac tivity for the title reaction versus x values could be set up: 0.1Ce>0.05Ce >0>0.05Eu>0.1 Eu congruent to 0.2Ce. The higher activity of Ce-doped cataly sts as compared to those doped with Eu was found to be related to the stren gth of the bond between oxygen and Co ions. (C) 2000 Elsevier Science B.V. All Fights reserved.