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Pure silica CHA-type zeolite (Si-CHA) membranes were synthesized by a hydrothermal secondary growth method on porous α-alumina supports. Using Si-CHA seed crystals as a crystalline nuclei allowed the formation of a dense Si-CHA layer. The Si-CHA membranes prepared in this study showed excellent gas permeance derived from their large pore volume and effective molecular sieve performance for gas separation. The Si-CHA membranes exhibited excellent H 2 and CO 2 permeance of 1.1 × 10 −6 and 1.7 × 10 −6 mol/m 2 sPa, respectively. The ideal selectivity of H 2 /CH 4 and CO 2 /CH 4 were 34 and 54, respectively. The stability test in the presence of water vapor on the Si-CHA membranes was performed and the Si-CHA membranes demonstrated good water vapor resistance, more so than the topologically analogous aluminosilicate zeolite membrane (SSZ-13). The Si-CHA membranes were unlikely to present pore blockages by water adsorption because of their hydrophobic pore systems.

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