This work investigated the permeation of binary gas mixtures in non-reducing (He/CO2) and reducing (H-2/Ar) conditions at temperatures ranging from 200 to 500 degrees C. A common performance aspect under both non-reducing and reducing conditions was that the He and H-2 purity in the permeate stream was independent of temperature for the tested binary gas mixtures, except at very high He/CO2 or H-2/Ar concentrations (>= 90/10) in the retentate stream. Under non-reducing conditions, the transport of gases was consistent with molecular sieving properties of silica derived membranes, and He permeance was constant irrespective of the He/CO2 binary concentration tested. An anomalous H-2 transport was observed under reduced conditions, as unexpectedly the H-2 permeance was higher for gas mixtures instead of single gas. Further tests showed that H-2 permeance increased 170% as the gas mixture changed from single H-2 gas to H-2/Ar gas mixtures. This was attributed to the experimental procedure, as the membranes were partially reduced each day and tested for gas permeation from pure H-2 to lower H-2 concentration in gas mixtures. Under these partial reducing conditions, H-2 slowly reacts with the surface of the dense Co3O4 particle, thus forming a porous CoO region. The increase in H-2 permeance was therefore attributed to improved pore connectivity between the silica structure and the porous CoO region. (C) 2015 Elsevier B.V. All rights reserved.