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

While the ambient N reduction to ammonia (NH) using HO as hydrogen source (2N+6HO=4NH+3O) 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 yield. Herein, we report a highly efficient catalytic system for ammonia synthesis using the low-temperature dielectric barrier discharge plasma to activate inert N molecules into the excited nitrogen species, which can efficiently react with the confined and concentrated HO molecules in porous metal-organic framework (MOF) reactors with V, Cr, Mn, Fe, Co, Ni and Cu ions. Specially, the Fe-based catalyst MIL-100(Fe) causes a superhigh NH yield of 22.4 mmol g h. 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 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.