Permeation properties and hydrothermal stability of silica–titania membranes supported on porous alumina substrates

A hydrothermally stable and H2-selective composite membrane was successfully prepared on a mesoporous alumina support by thermal decomposition of titanium isopropoxide (TIP) and tetraethylorthosilicate (TEOS) at high temperature. The membrane with a H2-selective silica–titania top layer of 10–20 nm in thickness had a H2 permeance 3 × 10−7 mol m−2 s−1 Pa−1 and a H2 selectivity over CH4 and CO2 in the range of 40–60. After 130 h exposure in 75 mol% H2O at 923 K, the H2 permeance was reduced by only 30%, compared to a pure silica membrane which suffered a loss of 90%. The use of the opposing reactants technique improved the quality of the composite membrane. Although considerable more efforts are needed to increase surface area, the stability properties suggest applicability of the composition at high temperature in the presence of high concentrations of steam.