Redox-controlled Ni-doped ε-MnO2 nanosheet catalysts for low-temperature oxidation of toluene and ethyl acetate

초록

Manganese dioxide (MnO2)-based catalysts have emerged as promising candidates for the complete oxidation of volatile organic compounds (VOCs). However, insufficient oxygen mobility and the limited availability of reactive oxygen species restrict their low-temperature catalytic performance. Herein, Ni-doped epsilon-MnO2 nano-sheet catalysts were synthesized via a redox-precipitation route under two distinct synthesis redox environments by tuning the KMnO4/Mn2+ ratio. The redox-controlled synthesis generates distinct surface chemistries, leading to different catalytic behaviors toward aromatic and oxygenated VOCs. Comprehensive structural, spectroscopic, and redox characterizations reveal that the catalyst synthesized under Mn2+-rich conditions possesses oxygen-vacancy-rich surfaces together with enhanced oxygen mobility and Mn-O-Ni redox interactions, which correlate with superior low-temperature oxidation of toluene. In contrast, the catalyst prepared under KMnO4-rich conditions exhibits more pronounced carbonate-modified surface chemistry, which is associated with enhanced ethyl acetate oxidation. The optimized catalysts achieve T90 values of 238 degrees C for toluene and 198 degrees C for ethyl acetate oxidation. Catalytic tests under an inert atmosphere further support the direct participation of catalyst oxygen species, consistent with a Mars-van Krevelen-type oxidation mechanism. Moreover, the catalyst synthesized under Mn2+-rich conditions maintains nearly complete ethyl acetate conversion for 48 h at 220 degrees C. These results demonstrate that controlling the synthesis redox environment provides an effective strategy to tailor surface chemistry and oxygen activation in Mn-based catalysts, offering new insights into the rational design of efficient catalysts for VOC oxidation.

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