| Summary: | Silica-based membranes prepared by chemical vapor deposition of tetraethylorthosilicate (TEOS) on γ-alumina overlayers are known to be effective for hydrogen separation and are attractive for membrane reactor applications for hydrogen-producing reactions. In this study, the synthesis of the membranes was improved by simplifying the deposition of the intermediate γ-alumina layers and by using the precursor, dimethyldimethoxysilane (DMDMOS). In the placement of the γ-alumina layers, earlier work in our laboratory employed four to five dipping-calcining cycles of boehmite sol precursors to produce high H<sub>2</sub> selectivities, but this took considerable time. In the present study, only two cycles were needed, even for a macro-porous support, through the use of finer boehmite precursor particle sizes. Using the simplified fabrication process, silica-alumina composite membranes with H<sub>2</sub> permeance > 10<sup>−7</sup> mol m<sup>−2</sup> s<sup>−1</sup> Pa<sup>−1</sup> and H<sub>2</sub>/N<sub>2</sub> selectivity >100 were successfully synthesized. In addition, the use of the silica precursor, DMDMOS, further improved the H<sub>2</sub> permeance without compromising the H<sub>2</sub>/N<sub>2</sub> selectivity. Pure DMDMOS membranes proved to be unstable against hydrothermal conditions, but the addition of aluminum tri-sec-butoxide (ATSB) improved the stability just like for conventional TEOS membranes.
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