Nickel‐Based Metal–Organic Frameworks for Coal‐Bed Methane Purification with Record CH4/N2 Selectivity

Abstract The enrichment and purification of coal‐bed methane provides a source of energy and helps offset global warming. In this work, we demonstrate a strategy involving the regulation of the pore size and pore chemistry to promote the separation of CH 4 /N 2 mixtures in four nickel‐based coordination networks, named Ni(ina) 2 , Ni(3‐ain) 2 , Ni(2‐ain) 2 , and Ni(pba) 2 , (where ina =isonicotinic acid, 3‐ain =3‐aminoisonicotinic acid, 2‐ain =2‐aminoisonicotinic acid, and pba =4‐(4‐pyridyl)benzoic acid). Among them, Ni(ina) 2 and Ni(3‐ain) 2 can effectively separate CH 4 from N 2 with top‐performing performance because of the suitable pore size (≈0.6 and 0.5 nm) and pore environment. Explicitly, Ni(ina) 2 exhibits the highest ever reported CH 4 /N 2 selectivity of 15.8 and excellent CH 4 uptake (40.8 cm 3 g −1 ) at ambient conditions, thus setting new benchmarks for all reported MOFs and traditional adsorbents. The exceptional CH 4 /N 2 separation performance of Ni(ina) 2 is confirmed by dynamic breakthrough experiments. Under different CH 4 /N 2 ratios, Ni(ina) 2 selectively extracts methane from the gaseous blend and produces a high purity of CH 4 (99 %). Theoretical calculations and CH 4 ‐loading single‐crystal structure analysis provide critical insight into the adsorption/separation mechanism. Ni(ina) 2 and Ni(3‐ain) 2 can form rich intermolecular interactions with methane, indicating a strong adsorption affinity between pore walls and CH 4 molecules. Importantly, Ni(ina) 2 has good thermal and moisture stability and can easily be scaled up at a low cost ($25 per kilogram), which will be valuable for potential industrial applications. Overall, this work provides a powerful approach for the selective adsorption of CH 4 from coal‐bed methane.