Cross-Scale Engineering of Single-Atom Catalysts from Local Planar Coordination to Spatial Architectures

Single-atom catalysts (SACs) enable high metal utilization and offer well-defined catalytic sites, yet their rational design is hampered by the instability of isolated atoms and an incomplete understanding of how structure governs performance. Early studies focused mainly on the first coordination sphere; however, catalytic behavior is also shaped by second-sphere interactions, support environments, extended spatial architectures, and their dynamic evolution. In this Review, we establish a cross-scale framework for the rational design of SACs across interconnected design dimensions: from in-plane to out-of-plane coordination; from primary coordination to through-bond secondary-sphere interactions, through-space microenvironments and metal-support interfaces; and from individual sites to macroscopic architectures governed by site density, intersite distance and topology. We further highlight directed dynamic reconstruction as an active design strategy that links as-synthesized structures with catalytically relevant working states. By integrating static structure, working-state evolution, and device operation, this Review provides insights into environment-dependent performance and guides the rational design of SACs across scales.