Physicochemical and catalytic properties in methane combustion of La1-xCaxMnO3±y (0≤X≤1; -0.04≤y≤0.24)

The objective of this work is to understand the role of physicochemical properties of pure and calcium substituted lanthanum, manganite perovskite with a particular attention to the importance of the degree of non-stoichiometry. The La1-xCaxMnO3 +/- y (0 <= x <= 1; -0.04 <= y <= 0.24) oxides were prepared by thermal decomposition of a liquid precursor of lanthanum and calcium nitrates and manganese acetate followed by calcination for 24 h at 973 K. XRD analysis showed that all samples were single-phase perovskite-type oxides with distorted structure depending on the substitution level. Presently, we have investigated the catalytic activities in methane combustion of this group of oxides. Bulk and surface physicochemical characteristics were determined and reported in this study. XPS analysis revealed the significant changes in the La3d, 4d; Ca2p; O1s and Mn2p characteristics as well as the excess of concentration with respect to the bulk resulting from the incorporation of Ca in La sublattice. Substitution with calcium affected significantly the surface specific area which ranged in 6-17 m(2)/g with a maximum value for an optimal composition x = 0.6. The light-off temperature for 50% methane conversion was found to be the lowest for La0.4Ca0.6MnO3.03 composition. Samples with oxygen overstoichiometry showed better catalytic performances (specific and areal activities) than those with oxygen substoichiometry. An optimal fraction, x = 0.6 of Ca enhanced significantly these performances. (c) 2004 Elsevier B.V. All rights reserved.