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

Alexander Y. Kryukov 1Anatoly V. Vishniakov 1Lucio Forni 2Cesare Oliva 2

1. D.I.Mendeleyev University of Chemical Technology of Russia (MUCTR), Miusskaya sq. 9, Moscow 125047, Russian Federation
2. Università di Milano, Dipartimento di Chimica Fisica ed Elettrochimica, via Golgi, 19, Milano 20133, Italy

Abstract

High surface area nano-sized catalysts with general formula La0.9M0.1CoO3 (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 Tf (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 Tf. 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 Tf. 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 La0.9Tb0.1CoO3. 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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Presentation: Poster at E-MRS Fall Meeting 2006, Symposium B, by Alexander Y. Kryukov
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-10 11:24
Revised:   2009-06-07 00:44
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