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

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2018, Vol.6 (29), p.14195-14206
• Main Authors: Yang, Yi, Li, Yuanzhi, Zhang, Qian, Zeng, Min, Wu, Shaowen, Lan, Lan, Zhao, Xiujian
• Format: Article
• Language: English
• Subjects: Abatement; Acetaldehyde; Acetic acid; Aluminum oxide; Byproducts; Catalysis; Catalysts; Catalytic activity; Catalytic oxidation; Durability; Ethyl acetate; I.R. radiation; Irradiation; Isotopic labeling; Manganese dioxide; Nanosheets; Oxidation; Oxygen; Palladium; Photoactivation; Platinum; Potassium permanganate; Selectivity; Ultraviolet radiation
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c8ta04274h

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.