Hydrogen permeation characteristics and stability of Ni-doped silica membranes in steam at high temperature

Ni-doped porous silica membranes of various Ni contents (Si/Ni = 4/1-1/1) were prepared by the sol–gel techniques for separation of H2 at high temperature around 500 °C. H2-selective permeation characteristics and hydrothermal stability of the membranes were tested in steam at 500 °C to show that hydrothermal treatments of the membranes before exposed to H2 were quite effective to prevent the further densification of Ni-doped amorphous silica networks due to reduction in H2 and sintering in steam (500 °C, 70 kPa). Ni-doped silica membranes (Si/Ni = 2/1) fired in the steamed atmosphere (partial pressure: 90 kPa) at 650 °C, for examples, were found to show a asymptotic steady permeance of 1.6 × 10−5 (m3(STP) m−2 s−1 kPa−1) for He and 4.6 × 10−6 (m3(STP) m−2 s−1 kPa−1) for H2 with a high selectivity of 1450 (He/N2) and 400 (H2/N2) even after kept in steam (steam: 90 kPa) at 500 °C for about 6 days. The permeance ratio of H2/H2O was found to be dependent not only on the permeance ratio of He/H2 but also on the Ni content, and the maximum permeance ratio observed was 37 for a Ni-doped silica membrane (Si/Ni = 1/1).