Structural Analysis of Single-Atom Catalysts by X-ray Absorption Spectroscopy

Metal nanoparticles (NPs) are one of the most frequently used heterogeneous catalysts. However, only the surface atoms in the NPs can participate in catalytic reactions. To maximize the atomic efficiency, the active sites can be reduced to single atoms. Generally, catalysts that have isolated metal atoms on the surface of a support are called single-atom catalysts (SACs). Many techniques have been developed and applied to probe the structures of SACs. Nevertheless, the structural characterization of SACs is still challenging as it requires the analysis of their structure and properties with atomic and sometimes even subatomic resolution. X-ray absorption spectroscopy (XAS) is a powerful tool in investigating the local coordination environment of SACs since it is element-specific and can provide accurate structural information at the subatomic level (∼0.01 Å).