Plasmonic Re-Excitation Enables Superoxide-Mediated Ethane Conversion to Acetic Acid under Visible Light

Radical-driven photocatalytic alkane upgrading is attractive yet suffers from poor selectivity due to unselective reactive oxygen species, making the precise steering toward milder, longer-lived superoxide (·O₂^-) over hydroxyl radicals a formidable challenge. Here, using WO₃ as a model semiconductor incapable of one-electron O₂ reduction to ·O₂^-, we show that coupling with plasmonic Au nanoparticles can re-excite photoelectrons to access the thermodynamically favorable superoxide route. This shift elevates reduction potential, sustains charge separation, and directs the formation of ·O₂^- and C₂H₅OOH intermediates, while weakened O₂ adsorption on Au allows ·O₂^- migration and selective redox C-O coupling. Consequently, Au-WO₃ achieves benchmark visible-light (λ > 420 nm) ethane oxidation with >80% selectivity and up to 100 mmol·L^-1 CH₃COOH. By steering oxygen activation away from unselective H₂O₂/·OH chemistry, this work demonstrates that plasmonic re-excitation enables controlled superoxide generation for selective oxygenate synthesis and establishes a general paradigm for overcoming the redox limitations of visible-light oxidation chemistry.