High‐Selectivity Y 2 O 3 ‐Doped SiO 2 Nanocomposite Membranes for Gas Separation in Steam at High Temperatures

Asymmetric structures were fabricated by depositing Y 2 O 3 ‐doped SiO 2 (Si/Y) membranes onto γ‐Al 2 O 3 supported by tubular α‐Al 2 O 3 . The thickness of the Y 2 O 3 ‐doped SiO 2 deposits was approximately 100 nm. The deposits/membranes have micropores with a pore diameter ~ <0.40–0.55 nm. Pore size distribution measurements were conducted directly on the membranes before and after hydrothermal treatment with a nano‐permporometer. The gas permeance properties of the membranes were measured in the temperature range 100°C–500°C. The Y‐doped SiO 2 membrane (Si/Y = 3/1) was found to exhibit asymptotically stable permeances of 2.39 × 10 −7 mol/m 2 /s/Pa for He and 6.19 × 10 −10 mol/m 2 /s/Pa for CO 2 , with a high selectivity of 386 (He/ CO 2 ) at 500°C for 20 h in the presence of steam. The Y‐doped silica membranes exhibit very high gas permeances for molecules with smaller kinetic diameters. The apparent activation energies of the H 2 permeance at 400°C were 24.2 ± 0.2 and 21.3 ± 0.7 kJ /mol for SiO 2 and Si/Y, respectively.