High surface area nano-sized catalysts with general formula La_0.9M_0.1CoO₃ (M=Ce, Pr, Tb) were synthesised by a novel flame-spray-pyrolysis method, based on spraying a solution of the corresponding metals salts (acetates in the present case, dissolved in propionic acid), together with oxygen, in a nozzle burner, where the mixed oxides particles form, followed by collection of the latter by means of an electrostatic precipitator.

All the prepared samples possessed the LaCoO₃ perovskite-like structure and consisted of 30-60 nm particles, lumped into larger (80-200 nm) agglomerates. Their surface area ranged from 45 to 60 m²/g. All of the catalysts showed a very high activity for the methane flameless combustion, attaining 100% conversion at a temperature T_f (temperature of full conversion) ranging between 495 and 515°C, depending on the nature of the M doping ions. The results of life-tests did not show any decreasing of catalytic activity after 50 h under reaction conditions at T_f. Thermal stability under high temperature exploitation was investigated by overheating the catalysts two times for 1h at 800°C in flowing reacting gas mixture (fast deactivation cycles) and then measuring again methane conversion at T_f. All the catalysts showed a more or less considerable decrease of activity, depending on chemical composition. For example, conversion after the second cycle decreased from 100% down to 80% for LaCoO₃ and to 48% for La_0.9Tb_0.1CoO₃. Taking into account the results of SEM analysis, this was attributed to sintering, connected with Gibbs instability of nano-sized materials.

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