Platinum single-atom catalysts: a comparative review towards effective characterization
Single-atom catalysis is a new frontier in the heterogeneous catalysis field due to its high activity and selectivity for various catalytic reactions. However, decades ago, single-atom catalysts could not be clearly visualized and characterized due to limitations associated with instrument resolution. In recent years, with the rapid development of characterization techniques, high-resolution scanning tunneling microscopy (STM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and other characterization techniques have been used to accurately represent single-atom catalysts. In this review, we discuss in depth these characterization techniques for Pt single-atom catalysts and focus on Fourier transformed EXAFS spectroscopy to study the coordination environment of Pt–M (M = Cl, O, C, N, S, Pt, Cu, Pd, Ni, Fe) for atomically dispersed Pt catalysts on diverse supports. We believe that this review will lead to better understanding of the effective characterization of Pt single-atom catalysts and promote further research on Pt single-atom catalysis in the future.