Molecular Trapdoor in HEU Zeolite Enables Inverse CO2‐C2H2 Separation

The adsorptive separation of molecules with very similar physical properties is always a challenging task. Reported herein is the design and tailoring of zeolite adsorbent for the precise discrimination and separation of CO2‐C2H2 mixture through the pronounced trapdoor effect. Typically, Sr exchanged K‐type clinoptilolite, namely Sr/K‐HEU, is developed as a robust zeolite adsorbent for inverse CO2‐C2H2 separation, showing the‐state‐of‐the‐art dynamic CO2/C2H2 selectivity of 48.0 and sustainable CO2 dynamic uptake of 0.96 mmol/g at the same time. The perfect recyclability and the intrinsic low‐cost nature of S/Kr‐HEU make it a promising candidate for practical applications. Three‐dimensional electron diffraction determines the precise structure of Sr/K‐HEU and density functional theory calculations reveal the intricate interplay between guest molecules and the gate‐keeping extraframework cations. Briefly, extraframework Sr2+ cations from the ten‐membered rings of HEU zeolites act as the molecular trapdoor, allowing the entry of CO2 molecules while excluding C2H2. This work presents a new example of molecular trapdoor in zeolite and its successful application in the challenging inverse CO2‐C2H2 separation, which not only expands the scope of molecular trapdoor concept but also improves current understanding on the nature of molecular trapdoor.