An apparatus for separating oxygen from an oxygen-containing gas and facilitating a chemical reaction with the separated oxygen includes a mixed conducting membrane, a porous body, and a material for catalyzing the reaction. The mixed conducting membrane has respective oxidation and reduction surfaces and is made of a non-porous, gas-impermeable, solid material capable of simultaneously conducting oxygen ions and electrons. At least the membrane and the catalyzing material are non-reactive with each other or are physically separated from each other during oxygen separation and the chemical reaction. The apparatus can be embodied by tubes, and a plurality of such tubes can form part of a reaction vessel in which various chemical reactions can occur benefiting from the apparatus design.