The Effect of Heat Treatment in Different Atmospheres on Tungsten-doped MnO(2)for Ozone Decomposition

摘要

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 degrees C) in three different atmospheres, i.e., air, helium, and hydrogen on a tungsten-doped MnO(2)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 degrees C or in helium at 300 degrees 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 degrees C) or helium (300 degrees C) made the exposed crystal facet change from (110) to (310) of alpha-MnO(2)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.