| Volatile organic compounds(VOCs)have become one of the most important air pollutants,it can not only cause indoor air pollution,but also have a bad effect on the atmospheric environment,causing photochemical pollution and causing serious harm to the human health.However,at present,catalytic combustion technology is considered to be one of the most effective methods to treat VOCs exhaust gas,which has high efficiency and no secondary pollution.The key of this method is the catalysts.The metal composite oxide catalysts have good economic and catalytic properties,which have important engineering application value.In some high humidity areas,the presence of water vapor will also have a certain effect on the activity of the catalysts.And in the process of VOCs reaction,a small amount of water vapor will be also produced,so it's necessary to study the influence of water vapor on the catalytic activity.The stability of the catalysts in the use of the process has an important impact on the production process.So the study on the thermal stability of the catalysts by adding Mg has important application value.The catalytic combustion characteristics of the catalysts in a fixed bed reactor were studied by using C u-Mn-Ce/?-Al2O3 as catalyst.It indicated that the effects of catalyst's structure and composition on catalytic activity were studied.It also discussed the effects of different reaction speed,loading,benzene concentration,calcination temperature and water vapor on the catalytic activity of the catalysts.Through the study on the activity of C u-Mn-Ce catalysts,the results showed that the molar ratio of C u-Mn-Ce with 1:1.5:0.5 had the highest catalytic activity,and the low concentration benzene could be complete ly transformed at 310?,and the catalytic activity was best when the calcination temperature was 600?.However,the activity of the catalyst decreased with the increase of the air speed.The addition of Mn promoted the low temperature activity of the catalysts,while the addition of Ce promoted the high temperature activity of the catalysts,and advanced the move of the lattice oxygen,which is conducive to the catalytic performance of the catalysts.The catalytic activity of Cu1Mn1.5Ce0.5 catalysts was significantly inhibited when the reaction stream contained water vapor.When the reaction temperature is 220?,the conversion efficiency of benzene is decreases by 8%.And with increase of water vapor concentration,the inhibitory effect is more obvious,but the activity of the catalysts can be recovered by N2 purging.The long the purging time is,the better the recovery is.After 1h by N2 purging,the conversion efficiency of benzene can be recovered to 95.4% at 320?,which can reach the initial conversion state(96.1%).The results showed that,under the influence of water vapor,the surface of the catalysts is easier to sinter,which can reduce the specific surface area of the catalysts.The competition between water molecules and benzene molecules can also inhibit the adsorption of benzene on the active sites of the catalysts,which is one of the reasons for the decrease of catalytic activity.On the other hand,in order to improve the thermal stability of the catalysts,by adding a small amount of Mg,the paper examined its impact on the performance of the catalytic combustion of benzene.It indicated that a certain amount of Mg can effectively improve the activity of the catalysts,which can increase the specific surface area of the catalyst by 2.1m2/g.When the reaction temperature is 200?,the catalytic activity over C u1Mn1.5Ce0.5Mg0.1 catalyst is increased by about 7% than that of the original catalyst.The studies showed that Mg ions on the surface of the catalysts mainly in the form of MgO,which can improve the thermal stability.And it has a strong interact with the carrier and the Mg2+,which made the structure of the catalyst stable,and made the sintering area of surface smal er,which can improve the catalytic activity.This paper studies the characteristics of catalytic combustion over Cu-Mn-Ce catalyst,and discussed the influence of water vapor,and through adding Mg,the thermal stability of catalyst was also discussed.Our research can provide the theory basis for the research and preparation of the catalysts. |
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