Facet Engineered α-MnO₂ for Efficient Catalytic Ozonation of Odor CH₃SH: Oxygen Vacancy-Induced Active Centers and Catalytic Mechanism

Abstract

The oxygen vacancy in MnO₂ is normally proved as the reactive site for the catalytic ozonation, and acquiring a highly reactive crystal facet with abundant oxygen vacancy by facet engineering is advisable for boosting the catalytic activity. In this study, three facet-engineered α-MnO₂ was prepared and successfully utilized for catalytic ozonation toward an odorous CH₃SH. The as-synthesized 310-MnO₂ exhibited superior activity in catalytic ozonation of CH₃SH than that of 110-MnO₂ and 100-MnO₂, which could achieve 100% removal efficiency for 70 ppm of CH₃SH within 20 min. The results of XPS, Raman, H₂-TPR, and DFT calculation all prove that the (310) facets possess a higher surface energy than other facets can feature the construction of oxygen vacancies, thus facilitating the adsorption and activate O₃ into intermediate peroxide species (O^2-/O₂^2-) and reactive oxygen species (•O₂^-/¹O₂) for eliminating adjacent CH₃SH. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) revealed that the CH₃SH molecular was chemisorbed on S atom to form CH₃S^-, which was further converted into intermediate CH₃SO₃^- and finally oxidized into SO₄^2- and CO₃^2-/CO₂ during the process. Attributed to the deep oxidation of CH₃SH on 310-MnO₂ via efficient cycling of active oxygen vacancies, the lifetime of 310-MnO₂ can be extended to 2.5 h with limited loss of activity, while 110-MnO₂ and 100-MnO₂ were inactivated within 1 h. This study deepens the comprehension of facet-engineering in MnO₂ and presents an efficient and portable catalyst to control odorous pollution.