Crystallinity‐Regulated Interplay Between Lattice Oxygen and Molecular Oxygen Enables Selective Superoxide Generation in Spinel Catalysts

ABSTRACT Catalytic oxidation mediated by lattice oxygen and molecular oxygen pathways represents an appealing route toward sustainable chemistry, yet achieving selective reaction outcomes by controlling reactive oxygen species (ROS) through catalyst structural design remains a fundamental challenge. In such systems, ROS can originate from both lattice oxygen and molecular oxygen, and their relative contributions determine ROS identity and reaction selectivity. Herein, NiMn 2 O 4 spinel oxides with tunable crystallinity are employed to elucidate how structural ordering regulates lattice oxygen reactivity and ROS evolution. Using sulfamerazine oxidation as a model organic oxidation reaction, the catalytic activity exhibits a volcano‐type dependence on crystallinity. An intermediate‐crystallinity regime, featuring coexisting crystalline and amorphous domains, facilitates balanced involvement of lattice‐ and molecular‐oxygen pathways. This structural configuration favors ROS evolution toward superoxide (•O 2 − ) generation while suppressing hydroxyl radicals (•OH). Conversely, excessive disorder disrupts charge transport, whereas high crystallinity imposes kinetic constraints on the participation of lattice oxygen. Combined in situ spectroscopy, atmosphere‐switching experiments, and density functional theory (DFT) reveal that crystallinity governs metal–oxygen interactions, oxygen vacancy formation, and lattice oxygen dynamics. These findings establish crystallinity as a pivotal parameter for regulating lattice‐ and molecular‐oxygen pathways and for designing spinel catalysts with controlled ROS selectivity.