Inverse CO 2 ‐C 2 H 2 Separation on the Low‐Silica CHA Zeolite Through Cooperative Cation and Gas Molecule Migration Mechanism

Abstract Inverse CO 2 /C 2 H 2 separation is promising for direct C 2 H 2 purification; however, designing cost‐effective and CO 2 ‐selective stable porous materials remains challenging. Herein, by precise Si/Al ratio design and inorganic cation regulation in low‐silica CHA zeolites, we achieve excellent inverse CO 2 /C 2 H 2 separation based on the trapdoor effect via a cooperative cation and gas molecule migration mechanism, distinct from the transient and reversible cation deviation previously reported. The designed K‐CHA exhibits high CO 2 capacity (3.51 mmol g −1 ) and much lower C 2 H 2 uptake (0.62 mmol g −1 ) at 298 K and 1 bar, achieving an ideal adsorbed solution theory (IAST) selectivity of 4350, outperforming most metal‐organic frameworks (MOFs) and zeolites. Breakthrough experiments confirmed the exceptional one‐step C 2 H 2 purification ability of K‐CHA, yielding a productivity of 662.9 mmol kg −1 . Rietveld refinement located cation positions within CHA. Density functional theory (DFT) calculations and ab initio molecular dynamics simulations (AIMD) elucidated the separation mechanism that CO 2 interacts more strongly with K‐CHA compared to C 2 H 2 , and the diffusion barrier for CO 2 passing through K⁺‐gated 8‐rings is lower than C 2 H 2 . AIMD further revealed distinct trajectories and synergistic migration of the door‐keeping K + ions and CO 2 /C 2 H 2 molecules during diffusion. This work provides new insights into the trapdoor mechanism, advancing our fundamental understanding.