An amorphous silica membrane with an excellent hydrogen/nitrogen (H 2/N2) permselectivity of >10 000 and a He/H2 permselectivity of 11 was successfully synthesized on a γ-alumina (γ-Al2O3)-coated α-alumina (α-Al 2O3) porous support by counter diffusion chemical vapor deposition using tetramethylorthosilicate and oxygen at 873 K. An amorphous silica membrane possessed a high H2 permeance of >1.0 × 10-7 mol·(m2·s·Pa)-1 at ≥773 K. The dominant permeation mechanism for He and H2 at 373-873 K was activated diffusion. On the other hand, that for CO2, Ar, and N2 at 373-673 K was a viscous flow. At ≥673 K, that for CO 2, Ar, and N2 was activated diffusion. H2 permselectivity was markedly affected by the permeation temperature, thickness, and pore size of a γ-Al2O3 mesoporous intermediate layer.
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