A novel K2NiF4-type oxide based on (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+d (PLNCG) dense mixed conducting ceramic membrane was successfully prepared through a solgel route. The oxygen permeation flux through the membrane swept by pure CO2 was comparative to that swept by He. The oxygen permeation and the stability of PLNCG under pure CO2 were investigated in detail. A membrane with a thickness of 0.8 mm was steadily operated for 230 h with a constant oxygen permeation flux of 0.32 mL/(min cm2) at 975 degrees C using pure CO2 as sweep gas. X-ray diffraction shows that PLNCG can maintain its fluorite phase, and no carbonates were observed, even when it was exposed to pure CO2 for a long time. (C) 2011 American Institute of Chemical Engineers AIChE J, 58: 24732478, 2012