Abstract
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.