Microwave-enabled low-temperature catalytic oxidation of toluene over a core-shell Fe₃O₄@MnO₂ catalyst

Low-temperature catalytic oxidation of toluene (<200°C) remains a significant challenge for VOCs abatement. Herein, a core-shell Fe₃O₄@MnO₂ catalyst with high microwave (MW) utilization efficiency is developed for MW-enabled low-temperature toluene oxidation, representing the first application of such core-shell MW absorbers to VOCs removal. Physicochemical and electromagnetic properties confirm that the core-shell architecture markedly enhances MW absorption and attenuation, enabling conversion of MW energy into catalytic activity. Compared with thermal catalysis, MW exhibits superior performance in 100-200℃ range (71.22-98.79% vs 24.90-61.74%), delivering accelerated kinetics and reduced activation barriers. Notably, Fe₃O₄@MnO₂ achieves a T₉₀ of 150℃ under MW catalysis and demonstrates enhanced SO₂/H₂O/NO resistances and stable operation over 24 h. DFT calculations reveal that Fe₃O₄@MnO₂ heterojunction promotes interfacial charge separation and transport, lowers oxygen vacancy formation and O₂ activation barriers, and strengthens toluene adsorption and C-H bond activation. Mechanistic investigations demonstrate that the MW-assisted oxidation proceeds via a synergistic pathway: ·OH-dominated radical oxidation governs the initial C-H bond cleavage and mineralization of gaseous intermediates, while O_lat-mediated non-radical oxidation dominates the deep oxidation of surface-bound intermediates. Furthermore, the distinct roles of MW thermal and non-thermal effects are clarified, and the degradation products and pathways are elucidated. This work demonstrates the advantages of MW for efficient toluene oxidation at low temperatures, expanding the use of MW absorbers into environmental catalysis and offering a promising strategy for VOC abatement.