The Effect of Heat Treatment in Different Atmospheres on Tungsten-doped MnO2 for Ozone Decomposition

Abstract

ABSTRACT Ozone penetrating from outdoors may cause indoor secondary pollution. The role and mechanism of heat treatment in improving the catalytic activity for ozone decomposition are not very clear. Here we investigated the effect of heat treatment (200–500 °C) in three different atmospheres, i.e., air, helium, and hydrogen on a tungsten-doped MnO2 catalyst (W-MnO2). The possible changes of crystal structure, morphology, specific surface area, chemical state, and surface functional groups were systematically checked, as well as their activities for ozone decomposition. It was found that the heat treatment in whichever atmosphere led to significant reduction of specific surface area and the amount of oxygen vacancies. However, the treatment in air at 400 °C or in helium at 300 °C did greatly improve the activity for ozone decomposition in humid conditions, while heating in hydrogen atmosphere did not change its humid-resistant activity. Heating-treatment in air (400 °C) or helium (300 °C) made the exposed crystal facet change from (110) to (310) of α-MnO2 and the irreversible removal of surface hydroxyl groups. While in a hydrogen atmosphere, no change of exposed crystal facet was observed, and the removed hydroxyl and water was revisable. In-situ DRIFTS observation of ozone decomposition indicated surface hydroxyl groups would transform into surface-adsorbed water, which is believed to affect the further decomposition of ozone. The present study not only clarifies the effects of heat treatment in different atmospheres but also demonstrates the necessity of irreversible removal of surface hydroxyl groups for improving the ozone decomposition activity in humid conditions.