One Iron for Two Iron Sites in a Metal-Organic Framework Toward Simultaneous N₂-H₂ Activation under Mild Conditions

Iron-based catalysts play an important role in the ammonia industry. As one of the most abundant iron minerals, Fe₃O₄ containing Fe^II and Fe^III sites is widely distributed in the earth's crust and even on exoplanets, theoretically giving it both economic and catalytic potentials in ammonia synthesis. However, in the absence of specific active co-catalyst and harsh conditions, Fe₃O₄ is impossible to achieve ammonia synthesis alone. Here, we designed to activate the relatively inert Fe^II and Fe^III sites in Fe₃O₄ with a third Fe^III site inlayed in a coordination framework (MIL-101(Fe)) to achieve the unpresented multi-site collaborative catalysis. In-depth mechanism study confirmed the roles of three different Fe sites in N₂ activation, H₂ activation, and product transfer, respectively. Efficient N₂-H₂ activation to NH₃ on the Fe₃O₄-based catalytic system has been achieved at extremely mild conditions. Our research provides a theoretical basis and a new strategy for designing efficient non-noble metal-based ammonia synthesis catalyst with minimized energy consumption.