Relationship between the Mesoporous Intermediate Layer Structure and the Gas Permeation Property of an Amorphous Silica Membrane Synthesized by Counter Diffusion Chemical Vapor Deposition

An amorphous silica membrane with an excellent hydrogen/nitrogen (H 2 /N 2 ) permselectivity of >10 000 and a He/H 2 permselectivity of 11 was successfully synthesized on a γ‐alumina (γ‐Al 2 O 3 )‐coated α‐alumina (α‐Al 2 O 3 ) porous support by counter diffusion chemical vapor deposition using tetramethylorthosilicate and oxygen at 873 K. An amorphous silica membrane possessed a high H 2 permeance of >1.0 × 10 −7 mol·(m 2 ·s·Pa) −1 at ≥773 K. The dominant permeation mechanism for He and H 2 at 373–873 K was activated diffusion. On the other hand, that for CO 2 , Ar, and N 2 at 373–673 K was a viscous flow. At ≥673 K, that for CO 2 , Ar, and N 2 was activated diffusion. H 2 permselectivity was markedly affected by the permeation temperature, thickness, and pore size of a γ‐Al 2 O 3 mesoporous intermediate layer.