<b>Fully inverse adsorption enables one-step high-purity C2H2 separation from ternary C2 mixtures in a robust porous crystal</b>
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Directly harvesting ultrahigh-purity acetylene (C<sub>2</sub>H<sub>2</sub>) from ternary C2 mixtures remains a significant challenge due to the intrinsic adsorption trend of conventional porous materials (C<sub>2</sub>H<sub>2</sub> > ethylene (C<sub>2</sub>H<sub>4</sub>) > ethane (C<sub>2</sub>H<sub>6</sub>)). 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<b> NTU-98,</b> featuring dual cages (~5.6 and 10.4 Å in pore size), fully reverses the adsorption trend of C2 hydrocarbons (C<sub>2</sub>H<sub>6</sub> > C<sub>2</sub>H<sub>4</sub> > C<sub>2</sub>H<sub>2</sub>), enabling direct production of ultrahigh-purity C<sub>2</sub>H<sub>2</sub> (>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 C<sub>2</sub>H<sub>4</sub> and C<sub>2</sub>H<sub>6</sub>, while concurrently weaken the affinity for the more polarizable C<sub>2</sub>H<sub>2</sub>. This work not only presents the first porous crystal capable of directly purifying C<sub>2</sub>H<sub>2</sub> from ternary C2 feeds, but also offers a generalizable blueprint for engineering microporous environments for challenging gas separations.
从三元C₂混合物中直接制备超高纯度乙炔（acetylene, C₂H₂）始终是一项极具挑战性的难题，这源于传统多孔材料本征的吸附亲和顺序为：乙炔（C₂H₂）> 乙烯（ethylene, C₂H₄）> 乙烷（ethane, C₂H₆）。为解决这一问题，我们提出了一种吸附调控策略，即通过微孔晶体的空间孔道环境工程化手段实现吸附行为的精准调控。我们采用经三氟甲基（trifluoromethyl）/甲基（methyl）功能化修饰的吡唑羧酸配体（pyrazole carboxylate ligand），合成了一系列结构稳定且孔道可精细调控的MOF-5（金属有机框架-5）类似物。其中一款命名为NTU-98的材料具有双笼孔道结构（孔径分别约为5.6与10.4埃），其完全逆转了C₂烃类的吸附亲和顺序：乙烷（C₂H₆）> 乙烯（C₂H₄）> 乙炔（C₂H₂），可在室温下通过单步流程直接从三元原料气中获得纯度超过99.99%的超高纯度乙炔。密度泛函理论（density functional theory）计算与载气晶体结构分析结果表明，在两个笼孔中精准定位的甲基基团可协同增强与饱和度更高的乙烯和乙烷之间的主客体相互作用，同时削弱对极化率更高的乙炔的结合亲和力。本研究不仅首次实现了可直接从三元C₂原料气中纯化乙炔的多孔晶体材料，更为极具挑战性的气体分离领域提供了一套可推广的微孔环境工程化方案。
