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

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Selective nitrogen capture by porous hybrid materials containing accessible transition metal ion sites, Nature Materials, 19 décembre 2016

 

Natural gas, a fossil fuel composed mostly of methane, is a clean and cheap energy source. However, many natural gas reservoirs contain unacceptable quantities of nitrogen and so upgrading is required to meet the pipeline quality that specifies a nitrogen concentration of less than 4%. Natural gas upgrading is topical with the olefin/paraffin separation is one of themost pressing industrial issues with potentially considerable economic impact. The removal of nitrogen from methane is currently achieved by cryogenic distillation, at high cost (far more expensive than the amine capture of CO2) and high energy consumption. The use of adsorption phenomena and membrane technologies appears as an alternative cost- and energy-efficient solution to selectively capture N2. The recovery of N2 is a great challenge today in diverse applications related to the fields of energy, environment and medicine such as oil recovery, air separation and hydrogen production from gases emitted in the steel industry.

Although adsorption-based processes are promising formethane upgrading, the N2/CH4 separation is still far from optimal and there is a critical need to design efficient N2-selective adsorbents. At equilibrium, all existing adsorbents prefer CH4 to N2, even in the case of the Li-exchanged low-silica X zeolite (LiX), commercially used for air purification.

 

 

 

Inspired by the biomimetic and metal_dinitrogen chemistry concepts, this multidisciplinary fundamental study reveals that designing MOFs with unsaturated metal sites in their cages offers a unique opportunity to achieve highly efficient N2 capture. A proof of concept was provided with the mesoporous threedimensional cage-like MIL-100 with unsaturated Cr(III) sites, the first-ever adsorbent able to thermodynamically capture nitrogen over methane and oxygen with large N2 uptake and easy regeneration. This has been further validated on the chromium(III) terephthalate MIL-101(Cr) (refs. 22,29), which shows the same zeolite MTN topology and accessible unsaturated Cr(III) contained in larger mesopore cages as compared with those of MIL-100(Cr).

This paves the way towards new adsorption-based technologies in the fields of energy and environment. In addition, the manipulation ofmultifunctionalMOFs possessing both selectiveN2 binding and catalytic sites might lead to a leap forward to develop future enzymatic catalysts for N2 fixation to produce NH3 or other N-containing chemicals.

 

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Nature Materials, 19 décembre 2016

 

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, herewe 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 newhorizons to address several challenges in chemistry, including the design of heterogeneous biomimetic catalysts through nitrogen

 

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

 

JiWoong Yoon, Hyunju Chang, Seung-Joon Lee, Young Kyu Hwang, Do-Young Hong, Su-Kyung Lee, Ji Sun Lee, Seunghun Jang, Tae-Ung Yoon, Kijeong Kwac, Yousung Jung, Renjith S. Pillai, Florian Faucher, Alexandre Vimont, Marco Daturi, Gérard Férey, Christian Serre, Guillaume Maurin, Youn-Sang Bae and Jong-San Chang

 

Nature Materials, 19 décembre 2016

 

 

doi : 10.1038/nmat4825