Synergistic Multifunctional Sites in High-Nuclear Cluster-Based Metal-Organic Framework for Coal-Bed Methane Purification.

The extraction of methane (CH4) from coal-bed gas represents a promising yet technically challenging process, primarily due to the nearly identical molecular sizes and physical properties of CH4 and nitrogen (N2), which complicate their separation. Herein, we developed a highly stable Ni7 cluster-based metal-organic framework (Ni-MOF) with excellent acid-base stability for selectively separating CH4/N2 mixtures. Ni-MOF contains multiple binding sites including open metal sites, low-polarity methyl groups, nonpolar benzene rings, and exposed oxygen atoms in its two-dimensional (2D) cross-linked zigzag channels. Adsorption experiments demonstrated that activated Ni-MOF has a pronounced preference for CH4 over N2, accompanied by a good CH4/N2 selectivity under environmental conditions. Grand Canonical Monte Carlo simulations revealed that - cooperative interactions between CH4 molecules and various binding sites at the preferential adsorption position in Ni-MOF enhance its affnity for CH4 over N2. Dynamic breakthrough tests further confirmed the fine CH4/N2 separation performance of Ni-MOF under practical conditions. Furthermore, the pelletization of Ni-MOF with a polymer binder was also explored, and the experimental results showed that the formed samples can still maintain a certain degree of good separation performance. This study presents a promising material for industrial CH4/N2 separation while highlighting the critical role of tailored functional groups in addressing this challenging separation process.