Flower-like Polymorphic MnOx Constructed by In Situ L–T Transition with Superior Performance in the Catalytic Ozonation of Dimethyl Sulfide under Humid Conditions

Abstract

To improve the water resistance of manganese oxide (MnO_x) in the catalytic ozonation of dimethyl sulfide (DMS) under humid conditions, polymorphic MnO_x was synthesized based on δ-MnO₂ with reference to the in situ layer-to-tunnel (L–T) transition of minerals in a natural environment. The constructed polymorphic MnO_x(Mn–SH) possessed abundant α–δ (α(Mn)-O-δ(Mn)) interfaces and exhibited superior catalytic activity for the conversion of DMS, ensuring more than 91% of DMS removal under harsh conditions [relative humidity (RH) = 80%] and excellent stability after testing for 20 h (RH = 60–80%). In situ DRIFTS spectra and theoretical calculations demonstrated that α–δ interfaces facilitated the formation of active hydroxyl groups (−OH) through H₂O dissociation, which can participate in ozone (O₃) activation and avoid the deactivation caused by H₂O. Simultaneously, more Brønsted acid sites formed through H₂O dissociation, which promoted DMS adsorption and decomposition. This study gives an understanding of the role of α–δ interfaces in promoting activity for catalytic ozonation and provides a convenient strategy to construct polymorphic MnO_x with enhanced water resistance, which can be applied to existing MnO_x used for catalytic ozonation of sulfur-containing compounds from livestock farms and the petroleum industries.