SURFACE CHARACTERIZATION AND CATALYTIC PROPERTIES OF LA(1-X)A(X)MO(3)PEROVSKITE OXIDES .2. STUDIES ON LA1-XBAXMNO3 LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.2) OXIDES

Barium substituted lanthanum manganite perovskite-type oxides were pre pared by a liquid precursor method and characterized by X-ray diffract ion, oxygen desorption, and X-ray photoelectron spectroscopic studies. XPS analysis revealed the significant changes in the doublet characte ristics of the Ols peak (similar to 530 eV) resulting from the substit ution of Ba in LaMnO3. A well defined Ba3d spectra was seen only with more than 10 mol% substitution of Ba in La site. Methane oxidation rea ction was carried out in a flow reactor with a feed containing 0.28% C H4, 15% oxygen and balance helium. The conversion of methane was follo wed in the temperature range of 200 to 700 degrees C. The light-off te mperature for 50% methane conversion was found to be the lowest (490 d egrees C) for La0.9Ba0.1MnO3 composition. Temperature Programmed Desor ption (TPD) experiments of oxygen indicate two maxima centered around 320-550 degrees C and 650-760 degrees C respectively. In the low tempe rature oxygen desorption region, the peak maximum was found to shift w ith Ba substitution which also corresponded to the activity of methane . The results for oxygen chemisorption and surface composition of thes e samples are related to the methane oxidation properties.