Functionalized inorganic membranes for gas separation

A porous membrane for separation of carbon dioxide from a fluid stream at a temperature higher than about 200° C. with selectivity higher than Knudsen diffusion selectivity. The porous membrane comprises a porous support layer comprising alumina, silica, zirconia or stabilized zirconia; a porous separation layer comprising alumina, silica, zirconia or stabilized zirconia, and a functional layer comprising a ceramic oxide contactable with the fluid stream to preferentially transport carbon dioxide. In particular, the functional layer may be MgO, CaO, SrO, BaO, La<SUB>2</SUB>O<SUB>3</SUB>, CeO<SUB>2</SUB>, ATiO<SUB>3</SUB>, AZrO<SUB>3</SUB>, AAl<SUB>2</SUB>O<SUB>4</SUB>, A<SUP>1</SUP>FeO<SUB>3</SUB>, A<SUP>1</SUP>MnO<SUB>3</SUB>, A<SUP>1</SUP>CoO<SUB>3</SUB>, A<SUP>1</SUP>NiO<SUB>3</SUB>, A<SUP>2</SUP>HfO<SUB>3</SUB>, A<SUP>3</SUP>CeO<SUB>3</SUB>, Li<SUB>2</SUB>ZrO<SUB>3</SUB>, Li<SUB>2</SUB>SiO<SUB>3</SUB>, Li<SUB>2</SUB>TiO<SUB>3 </SUB>or a mixture thereof; wherein A is Mg, Ca, Sr or Ba; A<SUP>1 </SUP>is La, Ca, Sr or Ba; A<SUP>2 </SUP>is Ca, Sr or Ba; and A<SUP>3 </SUP>is Sr or Ba.