We present a practical strategy for fabricating asymmetric MOF–polymer composite membranes using two-dimensional ZIF nanoplates as a selective skin layer. Controlled nanoplate alignment and interfacial interaction enable high permeance while preserving molecular selectivity and compatibility with scalable polymer processing. We further demonstrate that ammonia exposure dynamically modifies ZIF framework flexibility and pore accessibility, leading to irreversible changes in separation performance. Importantly, the presence of impurities critically affects membrane stability and long-term operation. In addition, we show that elevated operating temperatures significantly enhance gas flux while maintaining membrane structure, enabling improved performance without changing membrane materials.