Catalytic activity for methane flameless combustion and thermal stability of nano-sized lanthanum cobaltites doped with Ce, Pr and Tb

High surface area nano-sized catalysts with the general formula La0 9M0 1CoO3 (M=Ce, Pr, Tb) were synthesised by a novel flame-spray-pyrolysis method. All the prepared samples possessed the LaCoO3 perovskite-like structure and consisted of 30-60 rim particles, but existing as large (80-200 nm) agglomerates. Their surface area ranged front 45 to 60m(2)/g. All the catalysts showed a very high activity for methane flameless combustion, attaining 100% conversion at temperatures T-f, between 495 and 5 15 degrees C, depending on the nature of the M doping ion. The results of life-tests did not show any decreasing of catalytic activity after 50 It under the reaction conditions at T-f. The thermal stability under high temperature application was investigated by overheating the catalysts twice at 800 degrees C for 1 hr in a flowing reacting gas mixture, fast deactivation cycles, and then measuring methane conversion at T-f. All the catalysts showed a significant decrease of activity, depending on the chemical composition. Taking account of the results of SEM analysis, this was attributed to sintering, connected with the Gibbs instability of nano-sized materials.