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(1-3), and adsorptive purification of natural gas and air(4-6). Many transition metal-dinitrogen complexes have been envisaged for biomimetic nitrogen fixation to produce ammonia(3). Inspired by this concept, here we report mesoporous metal-organic framework materials containing accessible Cr(III) sites, able to thermodynamically capture N-2 over CH4 and O-2. This fundamental study integrating advanced experimental and computational tools confirmed that the separation mechanism for both N-2/CH4 and N-2/O-2 gas mixtures is driven by the presence of these unsaturated Cr(III) sites that allows a much stronger binding of N-2 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.