Electrostatic Surface Engineering in a Robust MOF Sieve for One‐Step Ternary C 2 H 4 Purification and Reverse CO 2 /C 2 H 2 Separation

One‐step production of high‐purity light hydrocarbons without a desorption process represents an advanced purification strategy. However, the development of efficient adsorbents is highly desired but remains challenging. Herein, a novel MOF adsorbent (Cd‐TIB) features a multi‐cage pore architecture with narrow apertures serving as C 2 H 4 sieves and predominantly electropositive cavity surfaces favoring CO 2 over C 2 H 2 . Notably, Cd‐TIB achieves an ideal CO 2 > C 2 H 2 ≫ C 2 H 4 adsorption sequence, enabling one‐step C 2 H 4 production from ternary C 2 H 2 /CO 2 /C 2 H 4 mixtures and reverse C 2 H 2 recovery from CO 2 /C 2 H 2 mixtures. The framework effectively excludes C 2 H 4 , delivering exceptional CO 2 /C 2 H 4 (9.6) and C 2 H 2 /C 2 H 4 (8.3) uptake ratios with high selectivities of 183.76 and 43.56, respectively. Moreover, Cd‐TIB exhibits preferential CO 2 adsorption (41.55 cm 3 /cm 3 ) over C 2 H 2 (36.06 cm 3 /cm 3 ) at 1 bar and 298 K, demonstrating a CO 2 /C 2 H 2 selectivity of 5.31. Modeling studies reveal distinct diffusion barriers and specific electrostatic interactions that govern the unique adsorption behaviors. Dynamic breakthrough experiments confirm its dual‐functional separation performance, directly yielding high‐purity C 2 H 4 (> 99.95%) and C 2 H 2 (> 99%) with excellent cyclability and stability under both dry and humid conditions.