Preparation Of Mn/TiO₂ Catalyst And Its Dechlorination Performance

Pollution prevention and abatement of volatile organic compounds?VOCs?is an urgent issue within the current air pollution control situation in China.Chlorinated volatile organic pollutants?CVOCs?,for its great harm on ecological environment and human health,have attracted much attention.Catalytic combustion is one of the most effective methods to decompose CVOCs,which can completely degrade them into inorganic matter under certain temperature conditions.Yet there are still some suspended problems such as catalyst poisoning and multi chlorinated byproducts.Therefore,it is necessary to develop a catalyst for the efficient decomposition of CVOCs.Spherical TiO₂ was prepared by adding salt solution with butyl titanate as raw material.MnO_x/TiO₂ catalyst was prepared by precipitation and precipitation method.The influence of atomic ratio of Mn/Ti,calcination temperature,calcination atmosphere,carrier morphology and additive dosage on the oxidation activity was studied.The structure,morphology and surface chemical properties of the catalyst were studied by scanning electron microscopy?SEM?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?and hydrogen-programmed temperature reduction?H₂-TPR?.The results show that the catalyst with the 0.6 atomic ratio of Mn/Ti,under the condition of 450 ? air calcination 4 h has high catalytic activity on degradation of chlorobenzene.The valence of metal ions in MnO_x/TiO₂ catalyst plays a positive role in the reaction,and the surface of catalyst has a large number of reactive oxygen species.The catalyst activity is optimized.As a result of experiment:95%of chlorobenzene can be conversed with a loading of 0.2 g the catalyst in an atmosphere of N2?80%?+ O2?20%?at 250 ?.The conversion of chlorobenzene remained above 90%during 900 min,which showed a fine catalitic perfomance and stability.Spherical carrier is beneficial to the dispersion of active components and exposure of active sites,to some extent to promote the catalytic decomposition of chlorobenzene performance,Ce,Cu additives to a certain extent,improve the anti-poisoning ability of the catalyst.The effects of catalytic combustion conditions on the catalytic degradation of chlorobenzene were systematically studied.The reaction process mainly investigated the initial concentration of pollutants,oxygen content,water vapor content,reaction temperature and Ce,Cu as auxiliaries and the impact of the addition.The results show that the catalytic material is more suitable for the treatment of low concentration chlorine containing gas,and the higher oxygen content makes the active lattice oxygen of the catalyst be fully supplemented,and then obtain high catalytic activity.The catalytic activity of water vapor is higher than that of anhydrous system because of the competitive adsorption of water vapor and pollutants.With the increase of temperature,the activation energy required for the reaction is reduced,and the catalytic activity is enhanced.Mechanism study of chlorobenzene catalytic oxidation on MnO_x/TiO₂ surface was introduced by combining oxygen switch experiment,various material characterization methods and pollutant analysis techniques.First chlorobenzene was adsorbed on the surface of the catalyst,in the Mn4+/Mn3+and lattice oxygen under the action of dechlorination to form benzene ring and inorganic chloride.The benzene ring was decarburized by hydroxyl radical and the oxidative activity of the catalyst to produce intermediate product,and finally oxidized to form CO₂,H₂O and other small molecules.