Single-Atom Catalysis

Single-atom catalysts (SACs) are gaining significant attention in organic synthesis, providing a bridge between homogeneous and heterogeneous catalysis. These systems consist of individual metal atoms dispersed on solid supports, mimicking the precision and selectivity of ligand-based organometallic complexes. Compared to conventional catalytic systems based on supported metal nanoparticles, SACs offer several advantages, including efficient utilization of metal atoms, high stereo-, regio-, and chemoselectivity, and enhanced stability. Moreover, in contrast to conventional homogeneous organometallic catalysts, SACs eliminate the need for complex ligands, while overcoming challenges related to catalyst recovery, air/moisture sensitivity, and long-term structural integrity. The design of the support plays a critical role in maintaining atomic dispersion and preventing metal atom aggregation in SACs, with materials such as carbon nitrides, covalent organic frameworks, and metal-organic frameworks commonly employed to achieve this atomic-level dispersion. Advanced characterization techniques like aberration-corrected electron microscopy and X-ray absorption spectroscopy have been essential in studying SACs at the atomic level, allowing researchers to fine-tune their properties for targeted synthetic applications. This chapter provides an introduction to the principles, advantages, and applications of SACs, highlighting their potential in sustainable catalytic processes.