Fe/Mn-based perovskite-type oxides with excellent oxygen permeability and reduction tolerance

A family of Co-free, Fe/Mn-based perovskite-type oxides, (Sr, A')(Fe, Mn)O3-delta (A'=La, Ba, Ca), was synthesized, and their oxygen permeability and phase stability in reducing atmosphere were investigated. The substitution of Mn at B site caused the decrease in oxygen permeability. As for the effect of A-site substitution, prominent promotion was observed by the substitution of Ba for 30% of Sr, and Ba0.3Sr0.7FeO3-delta was found to be one of most excellent oxygen permeable materials with the permeation flux of 3.0 cm(3) (STP) cm(-2) min(-1) at 900 degrees C. Reduction tolerance was evaluated by TG measurements in a 5%H-2/N-2 stream up to 1000 degrees C. After the TG measurements, crystal structures of La-Sr-Co-Fe-O and Sr-Fe-(Mn)-O perovskites were decomposed or transformed into low oxygen permeable phases, but the perovskite-type structure of Ba-Sr-Fe-(Mn)-O survived. The Fe/Mn-based perovskites with high oxygen permeability and exceeding reduction tolerance could be used as stable membrane materials for membrane reactors catalyzing NO-CH4 reaction and the partial oxidation of CH4 into synthesis gas.