A multilayer composite ceramic membrane was prepared by depositing a nano-scale layer of SiO2 on top of a modified porous alumina support by chemical vapor deposition (CVD) method. The modification of the support was carried out by adding a graded layer of Al2O3 (γ-alumina phase), using sol-gel method. An optimized temperature of 700 K for intermediate layer calcination was gained by XRD analysis. Cross-sectional images obtained from SEM showed that the intermediate γ-alumina layer had a thickness of about 2 μm and the top selective silica layer was quite dense and uniform with a thickness of about 90-100 nm. Permeation tests showed a very good flux of 10-6-10-7 mol m-2 s-2 Pa-1 for H2 with selectivities over CO2, N2 and CH4 up to 500. By performing different tests with various deposition times, it was concluded that by changing CVD time from 3 h to 6 h H2/CO2 selectivity increased from 32 to 573, although H2 permeation flux reduced about 50 percent.
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