Single-atom and cluster catalysts for thermocatalytic ammonia synthesis at mild conditions.

Ammonia (NH 3 ) is closely related to the fields of food and energy that humans depend on. The exploitation of advanced catalysts for NH 3 synthesis has been a research hotspot for more than one hundred years. Previous studies have shown that the Ru B 5 sites (step sites on the Ru (0001) surface uniquely arranged with five Ru atoms) and Fe C 7 sites (iron atoms with seven nearest neighbors) over nanoparticle catalysts are highly reactive for N 2 -to-NH 3 conversion. In recent years, single-atom and cluster catalysts, where the B 5 sites and C 7 sites are absent, have emerged as promising catalysts for efficient NH 3 synthesis. In this review, we focus on the recent advances in single-atom and cluster catalysts, including single-atom catalysts (SACs), single-cluster catalysts (SCCs), and bimetallic-cluster catalysts (BCCs), for thermocatalytic NH 3 synthesis at mild conditions. In addition, we discussed and summarized the unique structural properties and reaction performance as well as reaction mechanisms over single-atom and cluster catalysts in comparison with traditional nanoparticle catalysts. Finally, the challenges and prospects in the rational design of efficient single-atom and cluster catalysts for NH 3 synthesis were provided.