Perovskite-type oxide membranes for the oxidative coupling of methane



A series of ion-conducting perovskites of the form [La1-xAx] [Co0.2Fe0.8] O3-δ (x = 0.4, 0.6 for A = Sr; × = 0.8 for A = Ba) were investigated for their use as a catalytic membrane for the oxidative coupling of methane (OCM). A-site cations consisting of La0.4Sr0.6 and La0.2Ba0.8 produce materials with the highest oxygen fluxes and result in C2+ selectivities of 50% at 1,098 K, which are significantly higher than those achieved with a powdered catalyst in a packed-bed reactor configuration. Selectivities in these materials appear to be limited by high oxygen ion recombination rates that compete for oxygen with the desired coupling reaction(s). The results also indicate that oxygen fluxes are not limited by diffusion, but by surface exchange rates at the oxygen-lean side of the membrane. The study on stability of these materials showed that all three perovskites could be reduced in a pure methane or ethane stream at 1,023 K, but they were totally stable under reaction conditions where oxygen is present.