Synergy of Tetraalkylammonium and Polyquaternium Enables Zeolite Membranes with Exceptional Gas Separation Performance

Crystalline microporous membranes and films hold great promise for separation and catalysis; but their molecular sieving performance is compromised by boundary defects generated during conventional hydrothermal/solvothermal synthesis. Herein, a dual‐ammonium synthesis (DAS) strategy is presented to fabricate high‐silica zeolite membranes, where novel polyquaterniums promote the nucleation within interparticle gaps, while a classic tetraalkylammonium facilitates zeolite crystallization. The synergistic interplay between the two ammoniums balances in‐plane and out‐of‐plane growth of the zeolite layer, yielding thin yet defect‐scarce zeolite membranes. The generality of the DAS approach is demonstrated by fabricating a couple of high‐quality SSZ‐13 membranes through the combination of the tetraalkylammonium with various polyquaterniums, introduced either in the gel or seed suspension. Compared to conventional single‐ammonium synthesis, the DAS strategy produces thinner and higher‐performance zeolite membranes in half the synthesis time. The optimized membrane achieves a CO 2 permeance of 1780 × 10 −9 mol m −2 s −1 Pa −1 and a CO 2 /CH 4 selectivity of 460 for an equimolar CO 2 /CH 4 mixture, surpassing most reported membranes. This work establishes the DAS strategy as an efficient and reproducible route to produce high‐performance zeolite membranes with broad applicability.