A bimodal catalytic membrane having a hydrogen-permselective silica layer on a bimodal catalytic support: Preparation and application to the steam reforming of methane

The steam reforming of methane for hydrogen production was experimentally investigated using catalytic membrane reactors, consisting of a microporous silica top layer, for the selective permeation of hydrogen, and an α-alumina support layer, for catalytic reaction of the steam reforming of methane. An α-alumina support layer with a bimodal structure, which was proposed for the enhanced dispersion of Ni catalysts, was prepared by impregnating γ-Al2O3 inside α-Al2O3 microfiltration membranes (1 μm in pore diameter), and then immersing the membranes in a nickel nitrate solution, resulting in a bimodal catalytic support. The bimodal catalytic support showed a large conversion of methane at a high space velocity compared with a conventional catalytic membrane with a monomodal structure. The enhanced activity of Ni-catalysts in bimodal catalytic supports was confirmed by hydrogen adsorption measurements. A bimodal catalytic membrane, i.e. a silica membrane coated on a bimodal catalytic support, showing an approximate selectivity of hydrogen over nitrogen of 100 with a hydrogen permeance of (0.5–1) × 10−5 m3 m−2 s−1 kPa−1 was examined for the steam reforming of methane. The reaction was carried out at 500 °C, and the feed and permeate pressures were maintained at 100 and 20 kPa, respectively. Methane conversion could be increased up to approximately 0.7 beyond the equilibrium conversion of 0.44 by extracting hydrogen from the reaction stream to the permeate stream.