Photocatalytic Cascade Nitrogen Fixation for Selective Purification of Methane‐Rich Coal‐Bed Gas Over a Bimetallic MOF

ABSTRACT CH 4 ‐rich coal‐bed methane (CBM) is often contaminated with N 2 , but their similar properties make conventional separation energy‐intensive and inefficient. Herein, we report a photocatalytic strategy for selective N 2 conversion over CH 4 , achieving simultaneous CBM purification and nitrogen valorization. A Co‐Ni metal‐organic framework (CoNi‐PYZ) features isolated bimetallic sites, where ligand/Co units donate electrons to Ni, establishing spatially separated reduction and oxidation centers. This structural motif drives a photocatalytic cascade nitrogen fixation that N 2 is first reduced to NH 3 at the Ni sites; subsequently, the generated NH 3 outcompetes CH 4 for the Co sites, leading to its oxidation to NO 3 – . This remarkable selectivity is governed by the high polarity and lone‐pair electron donation of NH 3 , favoring its adsorption over nonpolar CH 4 . Notably, the optimal catalyst achieves high activity under mild conditions without sacrificial agents, delivering NH 4 + and NO 3 – production rates of 599.8 and 199.8 µmol g − 1 h − 1 , respectively. Mechanism analysis reveals that ligand engineering optimizes the d‐band center to balance adsorption and desorption, thereby minimizing the rate‐determining step barriers for both half‐reactions, consistent with the Sabatier principle. This work provides a reaction‐driven alternative to traditional phase‐separation, establishing a novel paradigm for CBM upgrading coupled with selective N 2 transformation.