Turning Normal to Abnormal: Reversing CO₂/C2‐Hydrocarbon Selectivity in HKUST‐1

Abstract Metal–organic frameworks (MOFs) can efficiently purify hydrocarbons from CO₂, but their rapid saturation, driven by preferential hydrocarbon adsorption, requires energy‐intensive adsorption–desorption processes. To address these challenges, an innovative approach is developed, enabling control over MOF flexibility through densification and defect engineering, resulting in an intriguing inverse CO₂/C2 hydrocarbon selectivity. In this study, the densification process induces the shearing of the crystal lattice and contraction of pores in a defective CuBTC MOF. These changes have led to a remarkable transformation in selectivity, where the originally hydrocarbon‐selective CuBTC MOF becomes CO₂‐selective. The selectivity values for densified CuBTC are significantly reversed when compared to its powder form, with notable improvements observed in CO₂/C₂H₆ (4416 vs 0.61), CO₂/C₂H₄ (15 vs 0.28), and CO₂/C₂H₂ (4 vs 0.2). The densified material shows impressive separation, regeneration, and recyclability during dynamic breakthrough experiments with complex quinary gas mixtures. Simulation studies indicate faster CO₂ passage through the tetragonal structure of densified CuBTC compared to C₂H₂. Experimental kinetic diffusion studies confirm accelerated CO₂ diffusion over hydrocarbons in the densified MOF, attributed to its small pore window and minimal interparticle voids. This research introduces a promising strategy for refining existing and future MOF materials, enhancing their separation performance.