Facile synthesis of β-MnO2 via ozone oxidation for enhanced performance of toluene oxidation

In this work, a series of β-MnO2 catalysts is directly synthesized via ozone oxidation using the hydrothermal method. And the effect of hydrothermal temperature on catalytic activities of toluene oxidation is investigated. The catalytic evaluation shows that O3(HT)-160 prepared at 160 °C of hydrothermal temperature exhibits the best catalytic activity of toluene oxidation compared with other catalysts. By comparison of physicochemical properties, O3(HT)-160 possesses a bigger specific surface area and larger pore volume, which are beneficial to the adsorption and diffusion of toluene molecules. Meanwhile, O3(HT)-160 performs lower reductive temperature, higher ratio of Mn4+/(Mn3++ Mn2+) and Olatt/Oads and much more oxygen vacancies, which contributes to the cycle of redox ability, the complete oxidation of intermediates and the activation of oxygen. Moreover, combined with the results of in-situ DRIFTS and TD/GC–MS, the main intermediates are benzyl alcohol, benzaldehyde, benzoic acid and propylene glycol during toluene oxidation on O3(HT)-160. Furthermore, the catalytic mechanism is proposed for toluene oxidation on O3(HT)-160. This work provides a more convenient and simpler method to prepare β-MnO2 using ozone as the oxidizer compared with potassium permanganate and potassium persulfate.