| Summary: | Methyl-modified niobium-doped silica (Nb/SiO<sub>2</sub>) materials with various Nb/Si molar ratios (n<sub>Nb</sub>) were fabricated using tetraethoxysilane and methyltriethoxysilane as the silica source and niobium pentachloride as the niobium source by the sol–gel method, and the Nb/SiO<sub>2</sub> membranes were prepared thereof by the dip-coating process under an N<sub>2</sub> calcining atmosphere. Their microstructures were characterized and gas permeances tested. The results showed that the niobium element existed in the formation of the Nb-O groups in the Nb/SiO<sub>2</sub> materials. When the niobium doping content and the calcining temperature were large enough, the Nb<sub>2</sub>O<sub>5</sub> crystals could be formed in the SiO<sub>2</sub> frameworks. With the increase of n<sub>Nb</sub> and calcination temperature, the formed particle sizes increased. The doping of Nb could enhance the H<sub>2</sub>/CO<sub>2</sub> and H<sub>2</sub>/N<sub>2</sub> permselectivities of SiO<sub>2</sub> membranes. When n<sub>Nb</sub> was equal to 0.08, the Nb/SiO<sub>2</sub> membrane achieved a maximal H<sub>2</sub> permeance of 4.83 × 10<sup>−6</sup> mol·m<sup>−2</sup>·Pa<sup>−1</sup>·s<sup>−1</sup> and H<sub>2</sub>/CO<sub>2</sub> permselectivity of 15.49 at 200 °C and 0.1 MPa, which also exhibited great hydrothermal stability and thermal reproducibility.
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