Ammonia synthesis is structure sensitive, and a minute change in the catalyst structure would cause a dramatic change in activity. To date, none of the studies reveal the metal size effect at a subnanometer scale on NH₃ synthesis, and such investigation remains a challenge. Here, we report the synthesis of Ru catalysts with sizes ranging from single atoms, atomic clusters (ACCs), sub-nanometric clusters, to nanoparticles (NPs) by adjusting precursor and/or loading of Ru. Sub-nanometric Ru catalysts not only exhibit performance different from that of NPs but also follow a different route for N₂ activation. The strong intra-cluster interaction of Ru atomic clusters enables the formation of strong interactions of Ru d-orbitals with the σ and π orbitals of N₂ molecules, resulting in N₂ activation over Ru ACCs to occur more easily than that over Ru NPs. Consequently, Ru ACCs display an unprecedentedly high NH₃ synthesis rate and large turnover frequency at mild conditions.

氨合成是结构敏感的，催化剂结构的微小变化会导致活性发生巨大变化。迄今为止，没有一项研究揭示了亚纳米尺度上金属尺寸对NH ₃合成的影响，这种研究仍然是一个挑战。在这里，我们报告了通过调整前驱体和/或 Ru 负载量来合成尺寸范围从单原子、原子簇 (ACCs)、亚纳米簇到纳米粒子 (NPs) 的 Ru 催化剂。亚纳米Ru催化剂不仅表现出与NPs不同的性能，而且遵循不同的N ₂活化途径。Ru原子团簇的强团簇内相互作用能够形成Ru d-轨道与σ的强相互作用和N _2分子的π轨道，导致在 Ru ACCs 上的 N ₂活化比在 Ru NPs 上更容易发生。因此，Ru ACCs 在温和条件下显示出前所未有的高 NH ₃合成率和大的周转频率。