Effect of Nb content on hydrothermal stability of a novel ethylene-bridged silsesquioxane molecular sieving membrane for H ₂/CO ₂ separation

Silica-based microporous membranes for the separation of gases with relatively small kinetic diameters, like hydrogen, carbon dioxide, nitrogen and oxygen under harsh industrial processes, will offer great potential for integration in CO ₂ capture technologies. Development of membranes with integrated performances of permeability, selectivity and stability in the presence of hot vapor, is one of the prerequisites for their successful implementation. Herein, we reported a novel microporous hybrid silica membrane, fabricated through sol-gel deposition of an ethylene-bridged silsesquioxane layer on a multilayer porous support, by adjusting the amount of niobium alkoxide precursor. When the Nb content was less than 50% (in mole), both hybrid siliceous microporous networks and generated Lewis acid sites imparted very low CO ₂ permeance to the membrane while retaining its comparatively high H ₂ permeance. Dominant densification shall take effect when Nb content was higher than 50%, which leads to both low H ₂ permeance and H ₂/CO ₂ permselectivity. Hybrid silica membranes with niobium loading amount of 17% and 33% respectively, showed excellent stabilities in the presence of 150kPa steam under 200°C, as evidenced by steady H ₂ permeances and exceptionally high H ₂/CO ₂ permselectivities (>700) during long-term stability test up to 300h, which demonstrating a promising CO ₂ separation membrane.