Fully inverse adsorption enables one-step high-purity C2H2 separation from ternary C2 mixtures in a robust porous crystal

Directly harvesting ultrahigh-purity acetylene (C2H2) from ternary C2 mixtures remains a significant challenge due to the intrinsic adsorption trend of conventional porous materials (C2H2 > ethylene (C2H4) > ethane (C2H6)). To overcome this, we propose an adsorption-steering strategy that exploits steric pore-environment engineering in microporous crystals. By using the pyrazole carboxylate ligand functionalized with trifluoromethyl/methyl groups, we developed a series of MOF-5 analogs with robust structures and finely-tuned pores. One of them, named NTU-98, featuring dual cages (~5.6 and 10.4 Å in pore size), fully reverses the adsorption trend of C2 hydrocarbons (C2H6 > C2H4 > C2H2), enabling direct production of ultrahigh-purity C2H2 (>99.99%) from ternary feeds at room temperature, in one step. Density functional theory calculations and gas-loaded crystallographic analyses reveal that the methyl groups strategically positioned within both cages synergistically enhance host-guest interactions with the more saturated C2H4 and C2H6, while concurrently weaken the affinity for the more polarizable C2H2. This work not only presents the first porous crystal capable of directly purifying C2H2 from ternary C2 feeds, but also offers a generalizable blueprint for engineering microporous environments for challenging gas separations.