ELECTRIC AND CATALYTIC PROPERTIES OF DOPED LAMNO3

The electric conductivity and Seebeck coefficient of sodium and strontium doped LaMnO3 were measured as a function of temperature and partial pressure of oxygen. The electrical conductivity measurements of La1-xNaxMnO3 (x=0.1-0.4) suggest a semiconductor behaviour from room temperature to 800-900-degrees-C. Both the electric conductivity and XRD results indicate a decomposition of the perovskites at sufficiently reduced atmosphere. Thus, La0.8Na0.2MnO3 decomposes at P(O2) is similar to 10(-15) atm and P(O2) is similar to 10(-13) atm at 800-degrees-C, respectively, whereas La0.8Sr0.2MnO3 decomposes at P(O2) is similar to 10(-15) atm at 1000-degrees-C. At low partial pressures of oxygen the conductivity exhibits a P(O2)1/4 dependency for both sodium- and strontium-doped LaMnO3. At high partial pressures of oxygen the conductivity is nearly independent of the variation of P(O2). Positive Seebeck coefficients indicate p-type carriers in the perovskite oxides. The mobility of the carriers was calculated at 1000-degrees-C and 1 atm O2, assuming a small polaron model. For La1-xNaxMnO3 (x=0.1, 0.2) the CH4 conversion and C2-selectivity were measured in a quartz fixed-bed reactor as a function of temperature and partial pressure of oxygen. The results indicate a maximum selectivity to C2H4 at 820-degrees-C for both catalysts. It was observed that La0.8Na0.2MnO3 showed an increasing C2H4 selectivity and a decreasing CH4 conversion when the P(CH4)/P(O2) ratio increased.