Study On Catalytic Combustion For 1,2-dichloroethane Removal And Synergistic Ozone Decomposition Over Transition Metal Catalyst

In recent years,haze weather due to serious air pollution continually occurs across the whole country.It is greatly harmful for people's health.Fine particulate matters composed with VOCs are the most important factor in the formation of haze.Haze elimination and VOCs removal have become a hotspot on environment catalysis.In this paper,1,2-dichloroethane(1,2-DCE)was used as a model molecule to evaluate the efficient catalyst for CVOCs purification and establish the structure-activity relationship.The following paragraphs address the related research in details.1.Four kinds of HZSM-5-x(x represents the molar ratio of SiO2/Al2O3),commercial ?-Al2O3 and SiO2 loaded with 1 wt%Mn were prepared using an impregnation method for catalytic oxidation of 1,2-DCE.The sample 1Mn/ZSM-5-27(1 wt%Mn)with SiO2/Al2O3 ratio of 27 shows the lowest T90 of 248 ? and the highest yield to HC1(60%)and CO2(20%)for catalytic combustion 1,2-DCE.By further varying the Mn loading,it was found that the optimal 10Mn/ZSM-5-27 exhibited the best performance.The T90 is 239? and the yield of HCl and CO2 reach 65%and 37%respectively.Besides the yield of by-products is the lowest one.XRD,N2 adsorption-desorption,H2-TPR,NH3-TPD,TPO-TG and XPS were used to characterize of these samples.The suitable redox property associated with high amount of acid sites on 10Mn/ZSM-5-27 contributed to its enhanced activity.The deposition of carbon,organic chloride,and metallic chlorine oxide(MnOxCly)to cover the active sites were the reason of catalyst deactivation.Carbon can be burned at high temperature(>600 ?)under rich O2 atmosphere,while the adsorbed chlorine species can be removed by rising the temperature to higher than 500?.However,the formation of highly stable MnOxCly species was the key reason of irreversible deactivation.The mechanism of catalytic oxidation 1,2-DCE was studied by in-situ DRIFTS.Chloroethanol(Cl-CH2CH2-OH)and vinyl alcohol were the vital intermediates.Additionally,vinyl chloride was easy to be attacked by chlorine radical to produce several kinds of polychlorinated ethylene(C2HxCl4-x),which were the undesirable byproducts.Furthermore,the optimal sample 10Mn/ZSM-5-27 was tested by the long-term experiment which revealed that 10Mn/ZSM-5-27 was not only stable,but also possessed a good water-resisting property.2.Based on previous studies,the content of Mn in 10Mn/ZSM-5(SiO2/Al2O3=27)was reduced to 1 wt%(1Mn/ZSM-5)with 0.1 wt%Ru doping.By comparing HZSM-5,1Mn/ZSM-5 and 0.1Ru/ZSM-5,it was found that 0.1Ru1Mn/ZSM-5 had the lowest T90=241?,and the highest HCl yield(76%)and CO2 yield(58%)for catalytic combustion 1,2-DCE.The samples were characterized by H2-TPR and NH3-TPD.It was known that 0.1RulMn/ZSM-5 had strong redox ability and maintained the acid content of HZSM-5,which significantly improved the activity for elimination 1,2-DCE.With an increase the content of Ru,it was seen that Ru agglomeration existed on the surface of 1Mn/ZSM-5,which led to the increase of the polychloride by-product(C2HxCl4-x)yield in catalytic activity.XPS analysis of the spent catalysts showed that there was only a small amount of organochlorine and no metal chloride/metal chloride oxide on the sample with Ru.The addition of Ru improved the chlorine-resisting ability of the catalyst.Mn is more easily attacked by chlorine than Ru.The presence of Mn not only improved the redox properity,but also effectively protected Ru without the attack of chlorine.Long-term experiment revealed that 0.1Ru1Mn/ZSM-5 had stable activity for catalytic degradation of 1,2-DCE and good water water-resisting property.3.Taking manganese oxide as the main components SO42-was doped on manganese oxide to synthesize manganese oxide with super acidity.By comparing different manganese oxides(MnO2,Mn2O3,Mn3O4 and MnO),it was found that the MnO2 with high acidity and redox catalyzed combustion of 1,2-DCE with the highest activity,T90=385?,the highest yield of HCl(85%)and CO2(90%),and the lowest kinds and yields of by-products.The samples were characterized by XRD,N2 adsorption-desorption,H2-TPR,NH3-TPD,TEM and XPS.MnO2 showed excellent catalytic activity with relatively high specific surface area,strong redox and higher content of acid sites.Because of the existence of HSO4-on MnO2,the strong acid content of MnO2 is very high.After XPS analysis of the samples,it was found that the content of chlorine on the four kinds of manganese oxide increased with the increase of Mn2+in the structure of manganese oxide.The strong acidity and good oxidation reducibility of MnO2 could improve its chlorine resisted property.The higher content of Mn2+in the catalyst was,the higher amount of manganese ions(Mn3+ and Mn4+)in the high-value state was transformed from Mn2+.Therefore,Mn2+was easy to be attacked by chlorine species to generate manganese chloride and high-value manganese oxide.4.The MnO2 with molecular sieve structure(OMS-2)was studied for catalytic decomposition of ozone.The activity of OMS-2-0.7(MnO4-/Mn2+=0.7)was higher 92%under the high gaseous hourly space velocity(GHSV)of 500,000 h-1 and high relative humidity(RH=90%).By XRD,N2 adsorption-desorption,H2-TPR,SEM,TEM and XPS,it was found that OMS-2-0.7 showed excellent catalytic decomposition activity of ozone due to its high specific surface area,high concentration of oxygen vacancy and Mn3+and smaller crystal size.When ozone was introduced into 1,2-DCE catalytic combustion reaction atmosphere,the catalytic combustion activity on 10Mn/ZSM-5-27 was improved.The increasing ozone concentration can further improve the catalytic combustion activity.The promoting effect of ozone came from the catalytic decomposition ozone to form abundant reactive oxygen species on the active site of Mn on the surface of 10Mn/ZSM-5-27,which greatly improved the oxidability of the catalytic reaction system.Similarly,0.1Ru1Mn/ZSM-5 showed outstanding catalytic elimination of 1,2-DCE in ozone atmosphere.5.In order to improve the chlorine-toxicity resistance of the materials and the methods of treating compound pollutants,the research was carried out on selective catalytic combustion of 1,2-DCE and selective catalytic reduction of NO on a new type of CuO.The CuO(CuO-p)was synthesized by the template of Cu-containing MOF(HKUST-1).Compared with CuO(CuO-c)synthesized by traditional coprecipitation method,CuO-p was found to obtain higher specific surface area(15 m2/g),stronger redox,richer acidity and surface Cu'.Selective catalytic combustion of 1,2-DCE showed that the catalytic activity and the yield of CO2 and HC1 on CuO-p were higher than that of CuO-c.XPS analysis of the spent catalysts revealed that both kinds of CuO surface have a large amount of chlorine deposition.The content of chlorine on CuO-p(Clmin 1.30%,Clorg 1.85%)was much lower than that on CuO-c(Clmin 4.75%,Clorg 5.29%).So the formation of more CuCl/CuCl2 on CuO-c promoted deacon reaction and reduces active sites on CuO-c,which continuously decreased the selectivity of HCl and reduced the yield of CO2?CuO-p showed excellent low temperature activity in NH3 selective catalytic reduction of NO reaction.The turnover frequency was stable at 3.33×10-5?3.49×10-5 s-1 with long term reaction at 300?,and the selectivity of N2 reached 97%.Therefore,CuO-p was suitable for catalytic elimination of compound pollutants containing CVOCs(1,2-DCE)and NOx(NO).