Light-Induced Fe-LMCT Catalysis for Redox-Coupled Conversion of NOx and SO2 Mixture.

Abstract

The coexistent nitrogen oxides (NO_x) and sulfur dioxide (SO₂) in flue gas pose inherent challenges for simultaneous removal due to their disparate reactivities. Conventional sequential treatments for their simultaneous removal face major issues of catalyst deactivation and byproduct generation. Here, we develop a subtle strategy using light-induced ligand-to-metal charge transfer (LMCT) catalysis with Fe(II) ethylenediaminetetraacetic acid (EDTA-Feᴵᴵ) to achieve redox-coupled conversion of NO and SO₂ mixtures. LMCT excitation in EDTA-Fe^II induces directional charge separation under irradiation, routing photogenerated electrons (e⁻) to Feᴵᴵ for driving selective NO-to-N₂ conversion (selectivity: 99.89%), while photogenerated holes (h⁺) oxidize SO₂ to SO₄ ²⁻ (selectivity: 96.34%). This spatial segregation of redox pathways suppresses N₂O generation, enabling continuous operation with 90.3% NO and nearly 100% SO₂ removal efficiency. Mechanism studies reveal the LMCT-enhanced charge transfer from carboxyl/amino groups to Fe centers, while in situ EPR confirms the •SO₃ ²⁻ radical-mediated h⁺ scavenging that accelerates charge separation and utilization. This work establishes Fe-LMCT catalysis as a sustainable platform for gas-phase pollutants remediation, achieving unprecedented selectivity through precise redox pathway control.