Stability of La0.6Sr0.4Co0.2Fe0.8O3-δ Perovskite Membranes in Reducing and Nonreducing Environments

The chemical stability of perovskite La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 - δ (LSCF-6428) has been investigated in connection with its potential use as a catalytic membrane for the oxidative coupling of methane (OCM). Once a steady-state oxygen-defect gradient is established (15−20 h), these membranes are found to be very stable under air/nitrogen gradients at temperatures up to 960 °C and they respond instantaneously to temperature changes with an apparent activation energy of 159 kJ/mol. However, serious near-surface etching occurs when one side of the membrane is exposed to 100% CH 4 at 850 °C and atmospheric pressure, which resulted in dramatic increases in oxygen flux (a factor of 5). While this also caused an increase in the OCM reaction rate, the selectivity of C 2+ hydrocarbons fell from 40 to 10%. It is also shown that stable operation under OCM conditions is possible if CH 4 pressures are reduced to 0.1 atm but at a cost of C 2+ production rate.