The low temperature catalytic decomposition of gaseous ozone on Nano Manganese dioxides and the effect of phase structure

Abstract

Four nano manganese dioxides with different phase structures (α-, β-, γ-, and δ-MnO₂) were prepared by hydrothermal method and characterized by X-ray powder diffraction, surface area, H₂-temperature programmed reduction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The prepared catalysts were tested for ozone decomposition and found considerable activity difference, which was due to their change in the MnO₂ phase structure. The γ-MnO₂ showed 100 % ozone decomposition among the four catalysts, while α-, β-, and δ-MnO₂ catalysts exhibited 92, 70, 35 %, respectively after 480 min. The characterization results suggested that the decomposition of ozone is primarily dominated by the tunnel structure, surface oxygen vacancies and average oxidation state (AOS) of Mn rather than specific surface area and reducibility. However, the random tunnel structure of γ-MnO₂ has provided most active surface oxygen vacancies and the lowest AOS of Mn on the catalyst surface. Therefore, the γ-MnO₂ catalyst presented the highest ozone decomposition capacity among the other MnO₂ catalysts. Due to this, γ-MnO₂ may potentially be used as a catalyst in the purification of ozone contains waste gases as well as in the application of ozone assisted catalytic oxidation of volatile organic compounds.