The rate and selectivity of methane oxidation over La0.75Sr0.25CrxMn1−xO3−δ as a function of lattice oxygen stoichiometry under solid oxide fuel cell anode conditions

Perovskite-structured La0.75Sr0.25CrxMn1−xO3−δ (LSCM, x=0x=0, 0.25, 0.50, 0.75, and 1) is a potential anode material for direct hydrocarbon solid oxide fuel cells (SOFCs). A pulse reactor system was used to determine the catalytic activity and selectivity of LSCM toward methane total oxidation f between 700 and 900 °C in the absence of gas-phase oxygen. This replicates the SOFC anode environment, in which oxidation occurs through reduction of the oxide lattice. Activity and selectivity were characterized as a function of lattice oxygen stoichiometry, 3−δ3−δ. As 3−δ3−δ decreased, the selectivity toward total oxidation decreased for all compositions due to either a change toward partial oxidation or increased dry-reforming activity. The reaction rate and range of oxygen stoichiometry favoring total oxidation increased with increasing Mn content. This was accompanied by a decrease in both carbon formation and oxide stability. These measurements suggest that more-active catalysts are required for SOFC applications.