Harnessing Multiple Adsorption Sites in a Phosphonate Metal–Organic Framework for Efficient C₂H₂/Co₂ Separation

Due to their comparable molecular dimensions and volatility, distinguishing C 2 H 2 from CO 2 during purification remains a significant challenge in industrial applications. Achieving effective isolation of C 2 H 2 from binary mixtures of C 2 H 2 /CO 2 is therefore a critical objective in petrochemical processes. Herein, an adsorption mechanism enabling selective C 2 H 2 /CO 2 separation has been elucidated in the phosphonate metal–organic framework (MOF) Ni‐STA‐12. The high C 2 H 2 uptake and remarkable CO 2 selectivity of Ni‐STA‐12 arise from the synergistic effect of diverse adsorption sites distributed throughout its structure, including various oxygen atoms and open metal sites. The adsorbed C 2 H 2 interacts strongly with the exposed adsorption sites in the framework and its binding capacity is much larger than that of CO 2 . Dynamic breakthrough experiments demonstrated the practical potential for the separation of C 2 H 2 in mixtures, and excellent separation potential (Δ q ) demonstrating high C 2 H 2 recovery from C 2 H 2 /CO 2 mixtures. Theoretical calculations show the synergistic interaction of various oxygen atoms of the MOF with the open metal site Ni and the dominant role of uncoordinated oxygen atoms in the adsorption of C 2 H 2 .