Study On Efficient Catalytic Oxidation Of Dichloromethane And Resistance To Chlorine Poisoning Of The Catalyst

In recent years,air pollution has been regarded as one of the important environmental issues in China,which has drawn much attention to the government.After years of remediation,the emissions of major atmospheric pollutants such as nitrogen oxides?NO_x?,sulfur dioxide?SO₂?,and particulate matter have been significantly reduced.However,volatile organic compounds?VOCs?,as important precursors of photochemical smog and smog,have been proposed as one of the key pollutants to be monitored and controlled in China at this stage.Among them,chlorinated volatile organic compounds?CVOCs?,an important subspecies of VOCs,are widely derived from many occasions such as dry cleaning,medicine,organic synthesis,metal processing,and waste incineration.Most CVOCs have the characteristics of strong toxicity,easy to be enriched in the environment,and harmful to the environment and human body.Therefore,most of them have been listed as the priority of environmental pollution control by the United States,the European Union and China.It is instant to strengthen the controlling and management of CVOCs emissions,as well as the research on the treatment technologies of CVOCs.Currently,catalytic oxidation technology is considered to be one of the most promising control technologies for CVOCs,and development of catalysts with excellent performance is the core of this technology.It was found that the catalysts for CVOCs removal are still faced with many technical challenges such as insufficient removal efficiency at low temperatures,easy to produce toxic byproducts and easy to be inactivated.Therefore,studying the key factors to improve the catalytic oxidation performance of CVOCs,clarifying the deactivation mechanism of catalysts,and developing catalyst formulations with high activity,high CO₂ selectivity and high stability are the keys to further apply and popularize the catalytic oxidation technology.In this paper,dichloromethane?DCM?was selected as a model pollutant to develop a catalyst with good low-temperature activity,selectivity of CO₂ and resistence to Cl-poisoning.Therefore,relationships between the physical and chemical properties of ctatalytic active components and the catalytic oxidation performance of DCM were studied,the deactivation mechanism of the catalysts was revealed and a formulation of catalyst with excellent anti-chlorine toxic properties was developed.Finally,the effects of other pollutants in the flue gas on the catalytic oxidation performance of DCM were investigated in order to provide reference and guidance for the design of CVOCs catalytic oxidation technology catalysts.The main content in the full text are as follows:1.The catalytic oxidation performance of DCM on series of supported metal oxides catalysts(MO_x/Sn_0.2Ti_0.8O₂)was studied.The oxygen species and elemental valence distribution,acidity and redox properties on catalyst surface were analyzed and it was found that the degradation of DCM needs the cooperation between acid sites and redox sites of the catalysts.On this basis,the influence of acidity and redox properties of catalysts on adsorption,activation and deep oxidation of DCM was revealed.Finally,a key oxidizing active component RuO₂ which is suitable for DCM catalytic degradation and an important acidic active component WO_x which is hopeful to further improve the low temperature activity of the catalyst,were screened.2.The W₁T₁₀O_x and RuO₂/W₁T₁₀O_x catalysts were constructed to study the influence of Cl species on the catalytic performance of DCM over the catalysts.By analyzing the morphology and structures of the W₁T₁₀O_x catalyst before and after deactivation,it was found that the morphology and structures of the W₁T₁₀O_x catalyst were severely damaged during the reaction.According to the further analysis of elemental composition and chemical characteristics of W₁T₁₀O_x and W₁T₁₀O_x-used samples,it was found that the loss of W was the main cause for the deactivation of the catalyst.What's more,it was found that loading RuO₂ can promote the desorption of chlorine adsorbed on the catalyst surface during the reaction,restrain the loss of W,maintain the stability of morphology and structures of the catalysts,and improve its resistance to chlorine poisoning.3.Series of Ru-W/ST catalysts with different RuO₂ loadings were constructed on the research basis of two previous chapters.The effects of RuO₂ loading on Ru-W/ST catalysts on the catalytic oxidation performance of DCM was studied.It was found that simultaneous loading of WO_x and RuO₂ can greatly improve the catalytic oxidation activity and CO₂ selectivity of DCM.However,with the increase of RuO₂ loading,the overall acidity of the catalyst gradually decreased,and the promotion of DCM degradation activity gradually weakened,which resulted in the difficulty to further increase the catalytic activity when RuO₂ loading reached a certain level.Combining the analysis of element surface properties and redox performance of the catalyst,we found that there is a synergy between Ru and W,which benefit the complete degradation of DCM.In addition,the effects of VOCs,SO₂ and NO₂ in the reaction atmosphere on the catalytic oxidation performance of DCM were studied.It was found that the Ru-W/ST catalysts could achieve the coordinated removal of acetone,propane and dichloromethane,and the effects of SO₂ and NO₂ on the catalytic oxidation performance of DCM were also revealed.