Novel photoactivation and solar-light-driven thermocatalysis on ε-MnO2 nanosheets lead to highly efficient catalytic abatement of ethyl acetate without acetaldehyde as unfavorable by-product

Abstract

A sample of MnO₂ nanosheets with the akhtenskite structure (denoted as ε-MnO₂) was prepared by a redox reaction between KMnO₄ and Mn(NO₃)₂. It exhibited much higher catalytic activity than the commercial precious metal catalysts 0.5% Pt/Al₂O₃ and 0.5% Pd/Al₂O₃ in the catalytic abatement of ethyl acetate. In comparison with those of 0.5% Pt/Al₂O₃ and 0.5% Pd/Al₂O₃, the T₉₀ value (the reaction temperature at which the conversion of ethyl acetate was 90%) of the ε-MnO₂ sample was considerably reduced by 160 and 136 °C, respectively. Notably, the ε-MnO₂ sample exhibited highly efficient photothermocatalytic activity and excellent durability without the unfavorable by-product acetaldehyde in the abatement of ethyl acetate under UV-vis-IR irradiation. Even under IR irradiation with λ > 830 nm, it still exhibited efficient photothermocatalytic activity. The oxidation of ethyl acetate on the ε-MnO₂ sample under irradiation follows a mechanism of solar-light-driven thermocatalytic oxidation. A novel photoactivation effect was found to significantly increase the solar-light-driven thermocatalytic activity and considerably reduce the selectivity for acetaldehyde. The novel photoactivation effect was revealed by combining theoretical evidence from DFT calculations and experimental evidence from ¹⁸O₂ isotopic labeling, CO-TPR, and O₂-TPO. Lattice oxygen in the ε-MnO₂ sample takes part in the oxidation of ethyl acetate and plays a decisive role in the catalytic oxidation of ethyl acetate. Irradiation not only enhances the activity of lattice oxygen in ε-MnO₂ but also increases the amount of active lattice oxygen in ε-MnO₂, which thus significantly improves the catalytic activity and reduces the selectivity for acetaldehyde by accelerating the complete oxidation of acetaldehyde.