Effect Of Vanadium Or Tungsten Doping On The Catalytic Activity Of Manganese Dioxide For Ozone Decomposition

Long-term exposure to ozone pollution will do harm to human health.Outdoor ozone infiltration and indoor sources may lead to indoor ozone pollution.In order to reduce and avoid indoor ozone pollution,it is urgent to develop efficient,stable,safe and environmentally friendly catalytic materials for ozone decomposition at room temperature under humid conditions.In this paper,a series of vanadium or tungsten doped manganese dioxide catalysts were prepared by a one-step hydrothermal method.The effects of vanadium or tungsten doping and subsequent heat treatment on the morphology,structure and catalytic ozone decomposition performance of manganese dioxide were studied.The main contents and achievements of this paper are as follows:（1）The effect of vanadate on the hydrothermal synthesis of manganese dioxide from potassium permanganate and manganese acetate was studied.Compared with the undoped cryptomelane manganese dioxide,the crystallinity of V-Mn O₂ became weaker,the specific surface area increased,the exposed crystal surface gradually turned to high index crystal plane,the oxidation state of Mn decreased,the species of active oxygen on the surface increased,and the surface acidity enhanced.The catalytic decomposition performance of V-Mn O₂ was remarkable.The V-Mn O₂（0.15）with the best performance not only had stable catalytic activity for high concentration ozone under humid conditions,but also showed high and stable removal performance for ozone near actual atmospheric concentration（200 ppb）under normal air purification filtration rate（5.1 cm/s）after loaded on crude filter material.（2）The influence of tungstate on the hydrothermal synthesis of manganese dioxide from potassium permanganate and manganese acetate was investigated.The doping of tungsten made the sample change from nanorods to nanoparticles,the specific surface area larger,the exposed crystal surface gradually changed to high-index crystal surface,the oxidation state of manganese decreased,the species of active oxygen on the surface and the surface acidity increased.Tungstate reached the best catalytic decomposition activity at lower molar doping amount.W-Mn O₂（0.06）with the best oxygen performance exhibited stable catalytic decomposition of ozone at room temperature under both dry and humid conditions（50%relative humidity）.（3）The effect of heat treatment on W-Mn O₂（0.06）in air,helium and hydrogen atmosphere was studied.The specific surface area of W-Mn O₂（0.06）was significantly reduced by heat treatment,but the exposure of high index crystal surface was increased,and the surface hydroxyl group was effectively removed,thus the catalytic activity of ozone decomposition was significantly enhanced.The best effect of heat treatment at300°C in helium was achieved at 400°C in air atmosphere.The catalyst heated in hydrogen at 200°C showed excellent activity,but the decomposition performance decreased obviously with the increase of humidity due to the adsorbed water on the surface.Manganese dioxide is reduced to Mn₂O₃ or Mn₃O₄ with the lattice oxygen removal at higher heat treatment temperatures in either atmosphere,resulting in a significant decrease in catalytic ozone decomposition activity.