Development of metal-doped silica membranes for increased hydrothermal stability and their applications to membrane reactors for steam reforming of methane

Abstract

Hydrothermal stability is one of the most important technical challenges for hydrogen separation silica membranes. Metal doping into silica matrix was proposed, and it was found that Ni and Co were effective to improve the hydrothermal stability. Co-doped silica membranes showed a high permeance of 1.8×10-7 mol/(m2̇ṡPa) and H 2/N2 permeance ratio of 730 with hydrothermal stability (500 °C, steam partial pressure 300 kPa). Using hydrothermally stable silica membranes, permeation properties of helium, hydrogen and water vapor were examined based on the activation energy of permeation. The activation energy of H2 permeation correlated well with the permeance ratio of He/H2. The permeance ratios of H2/H2O of silica membranes are always larger than unity, although the kinetic diameter of hydrogen (0.289 nm) is larger than that of water (0.265 nm). Silica membranes were applied to bimodal catalytic membranes, which consisted of microporous silica top layer for selective permeation of hydrogen and a bimodal catalytic support layer where catalysts such as Ni were impregnated inside a bimodal support consisting of mesopores (γ-alumina) and macropores (α-alumina). Increased performance for production of hydrogen was confirmed by catalytic membranes for steam reforming of methane.