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

Perovskite type La_1 ? xSr_xMnO₃ (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 La_1 ? xSr_xMnO₃ 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.