Highly efficient removal of ozone by amorphous manganese oxides synthesized with a simple hydrothermal method

Amorphous manganese oxides (MnO_x) were synthesized by facile hydrothermal reactions between potassium permanganate and manganese acetate. Synthesis parameters, including hydrothermal time and temperature and molar ratio of precursors, significantly affected the ozone removal performance and structure property of MnO_x. Amorphous MnO_x-1.5, which was prepared at the Mn²⁺/Mn⁷⁺ molar ratio of 1.5 under hydrothermal conditions of 120°C and 2 hr, showed the highest ozone removal rate of 93% after 480 min at the room temperature, RH (relative humidity) = 80% and WHSV (weight hourly space velocity) = 600 L/(g·hr). The morphology, composition and structure of catalysts were investigated with X-ray diffractometer (XRD), Raman spectra, N₂ physisorption, field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (H₂-TPR), O₂ temperature-programmed desorption (O₂-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). It was confirmed that high catalytic activity of amorphous MnO_x for ozone removal was mainly ascribed to its abundant oxygen vacancies, high oxygen mobility and large specific surface area.