Selective nitrogen capture by porous hybrid materials containing accessible transition metal ion sites

Selective dinitrogen binding to transition metal ions mainly covers two strategic domains: biological nitrogen fixation catalysed by metalloenzyme nitrogenases, and adsorptive purification of natural gas and air. Many transition metal-dinitrogen complexes have been envisaged for biomimetic nitrogen fixation to produce ammonia. Inspired by this concept, here we report mesoporous metal-organic framework materials containing accessible Cr(III) sites, able to thermodynamically capture N₂ over CH₄ and O₂. This fundamental study integrating advanced experimental and computational tools confirmed that the separation mechanism for both N₂/CH₄ and N₂/O₂ gas mixtures is driven by the presence of these unsaturated Cr(III) sites that allows a much stronger binding of N₂ over the two other gases. Besides the potential breakthrough in adsorption-based technologies, this proof of concept could open new horizons to address several challenges in chemistry, including the design of heterogeneous biomimetic catalysts through nitrogen fixation.