Trace Propane Impurity Self‐Triggers Guest‐Adaptive Pore Engineering in an Ultramicroporous MOF for Gas Purification

Deep removal of trace propane impurities from light alkane streams represents a pivotal but challenging step in gas purification. Herein, we report a titanium‐based metal‐organic framework, 1a , which unveils an important method‐the trace propane impurity itself actively triggers guest‐adaptive pore engineering for its own efficient capture. Unlike conventional adsorbents relying on strong host‐guest interactions, 1a exhibits a lower isosteric heat of propane adsorption (18.8 kJ mol − 1 ) while achieving high ideal adsorbed solution theory (IAST) selectivity for C 3 H 8 /CH 4 and C 2 H 6 /CH 4 (e.g., 543.6 and 34.7 at zero coverage, respectively). Crucially, we demonstrate that trace propane can induce local electron density migration from organic linkers to titanium‐oxo clusters and triggers subtle pore expansion through a combination of in‐situ spectroscopic, diffraction, and computational techniques, etc. This self‐customizing behavior optimizes the propane's own diffusion and adsorption pathway at loading of 50 mbar. Breakthrough experiments confirm separation performance for a ternary CH 4 /C 2 H 6 /C 3 H 8 mixture, achieving ≥99.99% CH 4 purity. Impressively, shaped 1a /PAN (PAN = polyacrylonitrile) by using an appealing net‐fishing‐inspired electrospinning (NFIE) strategy reveals its fast diffusion behavior and rapid heat diffusion. This work highlights the often‐overlooked active role of trace impurities and establishes a novel paradigm of impurity‐directed pore engineering for energy‐efficient separations.