Dynamic Coordination Microenvironments of Fe Single-Atom Catalysts in Advanced Oxidation Processes: From Working-State Evolution to Pathway-Selective Regulation

Iron single-atom catalysts (Fe-SACs) offer an atomically defined platform for peroxide-based advanced oxidation, yet their reactivity is still frequently rationalized using coordination structures measured only before or after catalysis. Such static descriptors identify precursor sites but do not necessarily resolve the Fe configurations that carry turnover. This Review establishes a dynamic coordination framework that distinguishes resting structures, reaction-induced working states, and irreversible deactivation products. It examines how first-shell coordination, axial ligation, extended microenvironments, neighboring sites, and interfacial solvation govern the formation and interconversion of peroxide-bound, hydroxy, Fe-oxo, and electronically coupled Fe-oxidant states. Radical, high-valent Fe-oxo, singlet-oxygen, and interfacial electron-transfer pathways are treated as competing catalytic fluxes emerging from a shared working-state landscape rather than as fixed attributes of individual Fe-Nx motifs. Particular emphasis is placed on the evidence required to identify kinetically competent intermediates, distinguish reversible coordination adaptation from structural escape, and connect working-state populations with regeneration and lifetime. Coordination and microenvironment engineering strategies are then evaluated according to their ability to control pathway selectivity without compromising site recoverability. Covalent organic frameworks are discussed as molecularly programmable platforms that can integrate Fe-site definition, charge transport, solvation, and oxidant supply. The resulting structure–state–pathway–lifetime framework advances Fe-SAC design from static activity correlations toward predictive control of catalytic trajectories under realistic operating conditions.