Synthesis of High Metal Loading Single Atom Catalysts and Exploration of the Active Center Structure

Single-atom catalysts (SACs) have been rising recently as a new frontier in the catalysis field. Due to maximum atom utilization efficiency and tunable electronic structures, SACs exhibit highly distinctive catalytic performance from bulk counterparts. SACs with high metal loading will facilitate practical applications. To that end, this Review focuses on recent strategies to maximize metal loading. An appropriate substrate, mainly heteroatom-doped carbon materials, is the key to avoiding aggregation or sintering during synthetic procedures. The coordination site construction and spatial confinement strategies are adopted to prepare SACs with high metal loading. Advanced characterization techniques with atomic resolution are indispensable for identification of the exact structure of SACs. This is true, especially for the applications and challenges in developing in situ/operando characterization techniques at the atomic level, which are discussed in this Review. Moreover, it is fundamentally necessary to investigate the active center structure, which facilitates any design of efficient SACs that can maximize single-atom catalytic activity. Furthermore, this Review highlights challenges and prospects for development of SACs.