Controllable Synthesis of Different MnO2 Phases by a Precipitation Method for Effective Ozone Decomposition

It is challenging to controllably synthesize manganese dioxide (MnO2) in a facile routine for structure-oriented applications. Herein, γ-, α-, amorphous (a-), and δ-MnO2 are synthesized by the same liquid phase precipitation of KMnO4 and MnSO4 with tailored pH by KOH dosage and pH = 1 HCl washing. An ozone decomposition reaction is adopted as the catalytic activity evaluation probe, and a-MnO2 showed high efficiency of 80–90% to 100 ppm ozone during a 10 h test at weight hours space velocity of 1,200,000 mL g–1 h–1. The high activity can be attributed to its high specific surface area, low average Mn oxidation state, and abundant surface oxygen vacancy content. In addition, the activity decrease of a-MnO2 can be attributed to the accumulation of oxygen intermediates, as illustrated by in situ infrared spectroscopy, which however can be reactivated by simple 60 °C oven heating. These results provide a facile way to controllably synthesize differently crystallized MnO2, especially for highly efficient ozone decomposition catalysts.