Morphological impact of 1-dimensional to 3-dimensional manganese dioxides on catalytic ozone decomposition correlated with crystal facets and lattice oxygen mobilities†

Abstract

Ozone is a pollutant that has received widespread attention in recent years, and manganese dioxide (MnO₂) has been widely used for catalytic ozone decomposition. However, few studies have described the structure–activity correlation of different morphological types of MnO₂. In this study, a series of MnO₂ crystals (α-, β-, γ-, δ-, ε- and λ-MnO₂) were synthesized, and their catalytic activities on ozone decomposition (25 °C, dry air) were comparatively studied, which exhibited the order ε-MnO₂ > α-MnO₂ > γ-MnO₂ > β-MnO₂ ≈ δ-MnO₂ > λ-MnO₂. XRD and HRTEM results confirmed their diversities on the exposed crystal planes. It was confirmed that ε-MnO₂ with the (1 0 2) plane had the largest number of oxygen vacancies and the best oxygen mobility. These findings elucidated the favorable performance of ε-MnO₂ in the aforementioned tests. DFT calculations revealed the reaction mechanism, showing that ε-MnO₂ has the lowest energy barrier for the rate-determining O₂²⁻ desorption step (2.04 eV). This work illustrated the crucial role of oxygen vacancies and the mobility of lattice oxygen, shedding light on the strategies for rational design and control synthesis of effective catalysts for ozone elimination.