Nickel-Based Metal-Organic Frameworks for Coal-Bed Methane Purification with Record CH 4 /N 2 Selectivity

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 /N mixtures in four nickel-based coordination networks, named Ni(ina) , Ni(3-ain) , Ni(2-ain) , and Ni(pba) , (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) and Ni(3-ain) can effectively separate CH from N with top-performing performance because of the suitable pore size (≈0.6 and 0.5 nm) and pore environment. Explicitly, Ni(ina) exhibits the highest ever reported CH /N selectivity of 15.8 and excellent CH uptake (40.8 cm g ) at ambient conditions, thus setting new benchmarks for all reported MOFs and traditional adsorbents. The exceptional CH /N separation performance of Ni(ina) is confirmed by dynamic breakthrough experiments. Under different CH /N ratios, Ni(ina) selectively extracts methane from the gaseous blend and produces a high purity of CH (99 %). Theoretical calculations and CH -loading single-crystal structure analysis provide critical insight into the adsorption/separation mechanism. Ni(ina) and Ni(3-ain) can form rich intermolecular interactions with methane, indicating a strong adsorption affinity between pore walls and CH molecules. Importantly, Ni(ina) 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 from coal-bed methane.