Iron (Oxyhydr) Oxides in Heterogeneous Fenton Processes: Structure-Activity Relationships in Hydrogen Peroxide Decomposition Pathways

Iron (oxyhydr)oxides serve as foundational catalysts in heterogeneous Fenton systems, yet their catalytic efficacy varies significantly across distinct mineral species. This review systematically explores the structure-activity relationships governing these variations to provide a clearer understanding of the underlying catalytic mechanisms. The intrinsic physicochemical properties of various mineral phases are examined to elucidate how structural features influence the formation of reactive species, including the highly reactive hydroxyl radical, substrate-dependent high-valent Fe(IV)-oxo species, and selective singlet oxygen generated from hydrogen peroxide (H₂O₂) decomposition. Furthermore, recent optimization strategies aimed at overcoming kinetic barriers and enhancing reaction selectivity are summarized. The discussion concludes with an outlook on future research directions, including catalyst evolution under reaction conditions and the characterization of reactive intermediates, while providing a theoretical framework for the rational design of iron-based catalysts with enhanced stability and oxidative performance.