Surface properties and catalytic performance in methane combustion of Sr-substituted lanthanum manganites

Perovskite type La1-xSrxMnO3 (x = 0-0.5) oxides were prepared by the amorphous citrate process, characterised by X-ray diffraction, oxygen desorption, temperature-programmed reduction, infrared and X-ray photoelectron spectroscopic techniques, and tested for methane combustion within the 473-1073 K temperature range. Since catalyst activity was found to depend strongly on BET areas and to a lesser extent, on the degree of substitution (x), intrinsic activities were computed for La1-xSrxMnO3 catalyst series. Among the compositions investigated, the degree of substitution x = 0.2 showed the highest intrinsic activity within the temperatures explored. Characterisation techniques made possible to correlate catalytic performance with the structural characteristics of the oxides. The stability of Mn4+ is probably the most important parameter, but excess of oxygen and atomic surface composition should also be taken into account. (C)2000 Elsevier Science B.V. All rights reserved.