The Synthsis And Ozone Decomposition Activity Of Manganese Dioxide (Type OMS-2) Catalysts

As we all know, ozone is a double-edged sword. The ozone layer in the stratosphere can resist ultraviolet light to protect life on the Earth. However, tropospheric ozone is a common pollutant that causes health problems to human beings including neurological disease, increased frequency of respiratory symptoms and reduced immune system function. The major source of ground ozone comes from tail gas used for purification of wastewater and drinking water and other modern office equipment.Because it is safe, economical and efficient, catalytic decomposition is the most effective method for purifying waste gases containing ozone. MnO2 are reported to be among the most active catalysts for ozone decomposition. OMS-2 is a form of manganese dioxide with a one-dimensional tunnel structure composed of 2x2 edge-shared MnO6 octahedral chains, which are corner-connected to form 4.6x4.6 A tunnels. The properties of OMS-2 as a catalyst, such as the large surface area, mixed valence manganese species and excellent hydrophobicity, could be predicted to promote the catalytic decomposition of ozone.This study focuses on ozone decomposition activity of OMS-2 and M-OMS-2 catalysts under high relative humidity, which were synthesized using a hydrothermal approach. Characterization of OMS-2 was carried out using XRD, Raman, XAFS, N2 physical adsorption, SEM and H2-TPR.Among the OMS-2 catalysts, the OMS-2-Ac synthesized using MnAc2 as Mn2+ precursor showed the best catalytic activity for ozone decomposition (-80%) at RH=90% and this performance is better than those of OMS-2-NO3 and OMS-2-Cl catalysts. Acetate groups could prevent the aggregation of manganese oxide particles, which may introduce more defects. The ozone decomposition activity is lineally correlated with the amount of Mn3+ in the OMS-2. This indicates that Mn3+ play a key role during the decomposition of ozone.Among the M-OMS-2 catalysts, the Ce-OMS-2 synthesized using Ce(NH4)2(NO3)6 as Ce precursor showed the best catalytic activity for ozone decomposition (～100%) at RH=90%. Compared with Co-OMS-2, Ni-OMS-2, Cu-OMS-2 and Fe-OMS-2 catalysts, the Ce-OMS-2 catalyst undergoes the slight distortion of unit cell and has smaller Mn-Mn coordination numbers, larger surface area, which could provide more sites for the adsorption of ozone and thus improve the catalytic performance for ozone decomposition. Higher contents of surface Mn+ and surface oxygen is also the reason for the better performance of the Ce-OMS-2 catalyst. Due to the high activity of Ce-OMS-2 under RH=90% and space velocity of 600,000 h-1, it is a promising catalyst for purifying waste gases containing ozone under high-humidity conditions.