Mechanistic Study On The Catalytic Removal Of VOCs And NO_x Enhanced By Active Centers Regulation

With the rapid development of social economy,the energy consumption increased year by year.The problem of air pollution has brought severe challenges to China's economic and social development and people's life and health.As the most important primary energy in China,coal consumption and utilization will produce a large number of nitrogen oxides?NO_x?and volatile organic pollutants?VOCs?and other air pollutants.The emission intensity of pollutants per unit area in Beijing Tianjin Hebei,Yangtze River Delta,Pearl River Delta and other key areas is far higher than the national average level,which makes China's air pollution problems present as composite and compression type.Catalytic method is one of the most effective methods to control VOCs,NO_x and other pollutants,in which catalyst is the core of the technology.At present,the catalyst activity is insufficient at low temperature,which can not be put into normal operation,and it is difficult to ensure the standard emission of pollutants.The stability of complex flue gas conditions is poor,and it is difficult to achieve the coordinated control of multiple pollutants.Therefore,it is of great significance to develop novel VOCs and NO_x removal catalyst formulations,enhance the low-temperature activity of the catalyst,and realize the coordinated and efficient control of VOCs and NO_x and other pollutants.Based on the above problems,this paper studied the mechanism of catalytic removal of propane and NO_x on cobalt based catalysts,reveals the structure-activity relationship of the catalyst,identifies the key factors to enhance the low-temperature activity of the catalyst,and realizes the efficient simultaneous catalytic removal of propane and NO_x by using hierarchical combined system.The main results are as follows:1?Co was screened as the main active component.The effect of Coloading on catalytic oxidation of propane was studied,and the variation of surface active sites was revealed.The intermediate species of propane oxidation on Co oxide were identified by in-situ infrared experiment,and the reaction path of propane catalytic oxidation process was obtained.Combined with the reaction kinetics experiments of oxygen and oxygen free,the reduction steps of catalyst by propane was proposed to play an important role in the whole reaction.According to the predicted reaction path,we provided theoretical guidance for the design and modification of propane low-temperature oxidation catalyst.The enhancement mechanism of Co based oxide catalyst doping modification on propane oxidation activity at low temperature was studied.The effects of different Co/Ce ratios on the physicochemical properties and oxidation activity of the catalyst were revealed.The results show that Co and Ce have a good interaction and form a new active site connected by Co³⁺-O^2--Ce³⁺.It was clear that the key factor to enhance the low-temperature activity of the catalyst was to strengthen the conversion of Co³⁺?Co²⁺and the dissociation of oxygen in Co-O structure.2.The oxidation of soot in flue gas and the thermal stability of the catalyst were studied.It was found that the specific surface area of catalyst,active oxygen species and Co³⁺species were the key factors affecting the performance of soot oxidation.The influence of gas components on the oxidation performance of Cobased catalyst was also studied.The results showed that the active oxygen species adsorbed on the catalyst surface directly participated in the soot oxidation reaction and had stronger oxidation performance.Through accelerated aging experiments,the surface structure of Co_0.9Ce_0.1O_x catalyst was destroyed and the adsorption capacity of active sites was inhibited under high temperature conditions.The deactivation mechanism of Co_0.9Ce_0.1O_x catalyst caused by high temperature was clarified.3.Cobalt cerium catalyst and V/Ti catalyst with different V content were prepared.The SCR reaction performance and activation mechanism of the two catalysts at low temperature were studied.By mixing the two catalysts in different layers,the Cobased mixed catalyst system was constructed,and the NO_x removal efficiency was achieved in a wide temperature range.The denitrification efficiency was more than 90%between175-300?,which was significantly better than that of single cobalt cerium catalyst and vanadium based catalyst.The active component distribution,bed thickness,particle size and other structural parameters of the catalyst were optimized.The interaction mechanism between NO,NH₃ and propane was analyzed,and the simultaneous removal of propane and NO_x was realized.Finally,cordierite supported Co-Ce catalyst was prepared.It has good catalytic oxidation activity for propane,acetone,toluene and synergistic removal efficiency of NO_x in the pilot plant,which has a certain practical application value and prospect.