Oxygen storage capacity of La1-xA′xBO3 perovskites (with A′ = Sr, Ce; B=Co, Mn)-relation with catalytic activity in the CH4 oxidation reaction

The aim of this work was to study the effect of cation-substitution on the reducibility of the perovskite, as well as the effect on the catalytic activity for the CH4 oxidation reaction. Six perovskites (LaCoO3, LaMnO3, La1-x,SrxMnO3 (x = 0.2, 0.4), and La1-xCexMnO3 (x = 0.05, 0.1)) were synthesized by reactive grinding. The reducibility of the perovskite was studied by means of the oxygen storage capacity (OSC) measurement. OSC was performed at different temperatures on LaCoO3 and LaMnO3, in order to elucidate the different mechanisms of reduction involved at each temperature. The substituted samples showed that reduction profile is modified at high-substitution degrees;, however. no differences were observed on the OSC values (amount of most active oxygen, calculated after one pulse of CO) between the pure lanthanum sample and the substituted ones. Tested in the CH4 oxidation reaction, the LaCoO3 sample was found to present a little higher activity than LaMnO3, even if the cobalt-based sample presented a smaller specific surface area. Moreover, all the substituted samples presented very slightly higher activities than the pure LaMnO3 solid. Because of the supposed redox oxidation mechanism (Mars-Van-Krevelen), this agrees well with the OSC results obtained for the reducibility of the manganese on these samples, by which it was observed that substitution does not clearly affect the immediate reduction of the manganese. (c) 2004 Published by Elsevier B.V.