Metallic-ceramic composite membranes and methods for producing the metallic-ceramic composite membranes are disclosed. The metallic-ceramic composite membranes include the advantages of a metallic substrate relative to known ceramic substrates, such as high permeability, better mechanical properties, and corrosion resistance, and the advantages of a ceramic membrane, such as high permeability, high permselectivity, mechanic strength, and thermal stability. Therefore, a three-layer metallic-ceramic composite membrane, including a porous metallic substrate, a first, intermediate mesoporous γ-alumina membrane layer, and a second, top mesoporous γ-alumina membrane layer, is disclosed. Because of the high mechanical strength of the metallic-ceramic composite membrane and because the pores of the second mesoporous γ-alumina membrane have a narrow size distribution and average size of about 2.1 nanometers, the metallic-ceramic composite membrane can be used to separate gases, such as carbon dioxide (CO2), in high-pressure environments.