Morphological impact of 1-dimensional → 3-dimensional manganese dioxides on ozone catalytic decomposition correlated with crystal facet and lattice oxygen mobility

Abstract

Ozone is a pollutant that has received widespread attention in recent years, and manganese dioxide (MnO₂) has been widely used for ozone catalytic decomposition. However, few studies have described the structural-activity correlation of different types morphological of MnO₂. In this study, series of MnO₂ crystals (α-, β-, γ-, δ-, ε-and λ-MnO₂) were synthesized, and their catalytic activities on ozone decomposition (25 ^oC, dry air) were comparatively studied, which exhibited an order of ε-MnO₂ > α-MnO₂ > γ-MnO₂ > β-MnO₂ ≈ δ-MnO₂ > λ-MnO₂. XRD and HRTEM confirmed their diversities on the exposed crystal planes. It was confirmed that ε-MnO₂ with (1 0 2) plane has the largest number of oxygen vacancies and the best oxygen mobility. These findings elucidate the favorable performance of ε-MnO₂ in the aforementioned tests. DFT calculations reveal the reaction mechanism, showed that ε-MnO₂ has the lowest energy barrier for the decisive speed step O₂^2- desorption (2.04 eV). This work illustrated the crucial role of the oxygen vacancies and the mobility of lattice oxygen, which sheds light on the strategies of rational design and control synthesis of effective catalysts for ozone elimination.