Highly Efficient Nitrogen Reduction to Ammonia through the Cooperation of Plasma and Porous Metal-Organic Framework Reactors with Confined Water.

While the ambient N 2 reduction to ammonia (NH 3 ) using H 2 O as hydrogen source (2N 2 +6H 2 O=4NH 3 +3O 2 ) is known as a promising alternative to the Haber-Bosch process, the high bond energy of N≡N bond leads to the extremely low NH 3 yield. Herein, we report a highly efficient catalytic system for ammonia synthesis using the low-temperature dielectric barrier discharge plasma to activate inert N 2 molecules into the excited nitrogen species, which can efficiently react with the confined and concentrated H 2 O molecules in porous metal-organic framework (MOF) reactors with V 3+ , Cr 3+ , Mn 3+ , Fe 3+ , Co 2+ , Ni 2+ and Cu 2+ ions. Specially, the Fe-based catalyst MIL-100(Fe) causes a superhigh NH 3 yield of 22.4 mmol g -1  h -1 . The investigation of catalytic performance and systematic characterizations of MIL-100(Fe) during the plasma-driven catalytic reaction unveils that the in situ generated defective Fe-O clusters are the highly active sites and NH 3 molecules indeed form inside the MIL-100(Fe) reactor. The theoretical calculation reveals that the porous MOF catalysts have different adsorption capacity for nitrogen species on different catalytic metal sites, where the optimal MIL-100(Fe) has the lowest energy barrier for the rate-limiting *NNH formation step, significantly enhancing efficiency of nitrogen fixation.