Abstract：
While the ambient N2 reduction to ammonia (NH3) using H2O as hydrogen source (2N2+6H2O=4NH3+3O2) is known as a promising alternative to the Haber-Bosch process, the high bond energy of N≡N bond leads to the extremely low NH3 yield. Herein, we report a highly efficient catalytic system for ammonia synthesis using the low-temperature dielectric barrier discharge plasma to activate inert N2 molecules into the excited nitrogen species, which can efficiently react with the confined and concentrated H2O molecules in porous metal-organic framework (MOF) reactors with V3+, Cr3+, Mn3+, Fe3+, Co2+, Ni2+ and Cu2+ ions. Specially, the Fe-based catalyst MIL-100(Fe) causes a superhigh NH3 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 NH3 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.
摘要：
尽管使用H2O作为氢源（2N26H2O=4NH33O2）将环境N2还原为氨（NH3）被认为是Haber-Bosch工艺的有希望的替代方法，N=N键的高键能导致极低的NH3产率。在这里，我们报告了一种高效的氨合成催化系统，使用低温介质阻挡放电等离子体将惰性N2分子激活为活化的氮物种，它可以有效地与多孔金属有机框架（MOF）反应器中的受限和浓缩的H2O分子反应，Cr3+,Mn3+,Fe3+,Co2+,Ni2+和Cu2+离子。特别是,Fe基催化剂MIL-100（Fe）导致22.4mmolg-1h-1的超高NH3产率。在等离子体驱动的催化反应过程中，对MIL-100（Fe）的催化性能和系统表征的研究表明，原位生成的有缺陷的Fe-O团簇是高活性位点，并且在MIL-100（Fe）反应器内确实形成了NH3分子。理论计算表明，多孔MOF催化剂在不同的催化金属位点上对氮物种具有不同的吸附能力，其中最佳的MIL-100（Fe）对于限速*NNH形成步骤具有最低的能垒，显著提高固氮效率。
