Site inhomogeneity and structural dynamics of single-atom catalyst

Single-atom catalysts (SACs) have emerged as a frontier in heterogeneous catalysis owing to their maximum atom-utilization efficiency and unique catalytic properties. However, a simplistic understanding of the “single-atom” concept often masks their intrinsic complexity. This review aims to systematically discuss the key scientific issues confronting the field of single-atom catalysis, providing a conceptual framework for future research. We first dissect the inhomogeneity of active sites in SACs, revealing the “seeing is not always believing” principle, where minority species with high activity can dominate the overall catalytic performance. Subsequently, we explore strategies for precisely tuning the catalytic activity and selectivity by modulating the coordination microenvironment of the single-atom centers and constructing synergistic active ensembles. Furthermore, we highlight the dynamic evolution of SACs under realistic reaction conditions, emphasizing the critical importance of identifying the “true” active sites that are formed operando. Finally, we present an outlook on the future of the field, proposing that its ultimate goal is to transition from a trial-and-error approach to a new era of predictive, rational, and on-demand design of single-atom catalysts. This transition necessitates breakthroughs in the precisely controllable synthesis of uniform active sites, the development of quantitative characterization methods, data-driven catalyst design, and the dynamic control of active sites to expand the application boundaries of SACs in complex chemical transformations.