Fundamental Research Of Gaseous Chlorobenzenes And Dioxins Catalytic Decomposition Over Modified Titanium-based Catalysts

During the production and daily life of human,various pollutants are emitted inevitably.The pollutants with toxicity will damage the environment and ecology,thus arouse highly attention of the society in recent years.Now it is really urgent to develop and improve the pollutant emission control method and technology for disposing the pollutants in time.Catalysis technology can overcome the drawback of traditional active carbon adsorption method and achieve the complete mineralization of organic compounds,therefore it has been considered as a most potential end of the pipe control method.In this paper,several methods are employed to promote the activity of the catalyst for degrading the chlorobenzenes and dioxins at a relatively low temperature.Furthermore,the promotion mechanism during the catalytic reaction are discussed,the main conclusions are obtained as followed:?1?VO_x,MnO_x and CuO_x carried by TiO₂are employed to degrade the gasous chlorobenzenes seperately.The experimental results show that the MnO_x/TiO₂ catalyst with 12 wt%MnO_x loading and the CuO_x/TiO₂ catalyst with 4 wt%CuO_x loading show the high activities for chlorobenzene degradation and their activities are both higher than that of VO_x-WO₃/TiO₂ at,lower temperature.The characterization of the catalysts indicate that loading amount of the active constituent of the catalyst is not the only factor that determines the catalytic activity,the specific area,the pore size distribution,the average valence of the metal,the concentration of the adsorbed oxygen on the catalyst surface are all key factors influencing the catalytic activity.?2?The adding of MnO_x or CuO_x in the VO_x/TiO₂ catalyst both obviously improve the catalytic activity for the 1,2-DCBz,especially at the low temperature.The structure of Mn-O-Cu is detected when the the mixture of CuO_x and MnO_x are added in the VO_x/TiO₂ catalyst,this structure helps the improvement of the catalyst activity.At 200 ?,the VMnCu/T catalyst remove about 85%of the 1,2-DCBz.When the carbon nano tubes?CNTs?are added in the catalyst,the specific area of the catalyst increases a lot and the new catalyst remove 90%of 1,2-DCBz at 200?.?3?The end-products and intermediate products produced from the catalytic degradation of 1,2-DCBz are detected quantitatively.The results show that the formation of chlorobenzenes and chlorophenols with high chlorination may be the important reason that the 1,2-DCBz is hard to be degraded at low temperature,as these productions are more difficult to be degraded than the 1,2-DCBz.Trace PCDD/Fs with low chlorinations are generated during the catalytic reaction of 1,2-DCBz,when the reactions occur on the CNTs-containing surface,the formation of these PCDD/F congeners is more severe.On CuO_x-containing surface,especially on the surface both containing the CuO_x and CNTs,a lot of C2HCl3 and C2Cl4 are formed during the catalytic reaction of 1,2-DCBz,these two production may immobilize or remove the Cl on the catalyst,decreasing the risk of dioxins formation and the Cl-poisoning of the catalyst.?4?The ozone is employed to couple the catalyst for promoting the catalytic activity of conventional VO_x/TiO₂ catalyst.It is found that the decomposing rate of ozone is different on the different surfaces at the different temperatures.The transition metal oxides and the acid ion on the catalyst both increase the decomposing rate of ozone,while the rate has linear positive correlation with the degradation of 1,2-DCBz on the catalyst surface.The acid VWNT catalyst remove 98%of 1,2-DCBz at 160 ? coupling with ozone.Ozone can improve the activity of catalyst and the selectivity of CO evidently even though the ozone is in low concentration.When both the ozone and UV irradiation are coupled in the catalyst system,99%of 1,2-DCBz is removed at 160 ? in 1.8 seconds.?5?The VO_x/TiO₂ catalyst modified by CuO_x,MnO_x and CNTs is used to degrade the PCDD/Fs directly.The results show that in the simulated flue gas without ozone,the catalyst cannot degrade the dioxins efficiently,in opposite,the PCDD/Fs are generated on the catalyst.The PAHs molecules with high concentration in the simulated flue gas,the agglomeration of the added CNTs and the strong reducibility of the CNTs are all harmful to the degradation of PCDD/Fs and beneficial to the formation of PCDD/Fs.The adding of ozone in the simulated flue gas help to increase the activity of the catalyst and improve the degradation of PCDD/Fs.As the decomposing rates of ozone are different on the different transition metal oxides,when VMn/T-C and VCu/T-C catalysts work coupling with ozone,they show different performance at the different temperatures:the former catalyst shows higher activity when the reaction temperature is lower while the latter one shows higher activity at higher temperature.VMnCu/T-C catalyst has the highest activity to degrade the PCDD/Fs coupling with ozone,as ozone decomposes on it with a suitable rate,prolonging the lifetime of the produced oxygen species.At 220 ?,in simulated flue gas with a lot of PAHs molecules,the VMnCu/T-C remove and degrade 89%and 84%of PCDD/Fs respectively,at the same time,this catalyst could efficiently degrade all kinds of the PCDD/Fs with 4 to 8 chlorination.?6?In the actual incineration flue gas,the adding of CNTs and CuO_x in the VO_x/TiO₂ catalyst lead to the formation of PCDD/Fs while the adding of MnO_x or the mixture of MnO_x and CuO_x promotes the catalystic activity of the VO_x/TiO₂ for the degrading PCDD/Fs.Whether coupling with ozone or not,VMnCu/T catalyst shows the highest activity for the PCDD/Fs degradation in the actual incineration flue gas.