Study On Preparation And Catalytic Activity Of A Low Temperature High Activity Catalyst Ag/NiO_x-MnO₂

Nowadays,with the development of industrialization and the increase of vehicle emission,the content of benzene series in the environment is increasing.They have caused great harm to the human body and the environment.Catalytic combustion technology is one kind of effect methods for effective deal with benzene series pollutants.The key of this technology is obtained high-performance catalysts.In this dissertation,o-xylene is used as the target pollutant and nickel oxides and silver species are incorporated in type II Manganese oxide Octahedral Molecular sieve（OMS-2,）catalyst.The specific research content is as follows:（1）NiO_x-MnO₂ catalysts were prepared by synchronous oxidation reduction method using potassium permanganate,manganese acetate and nickel acetate as raw materials.The influences of Ni/Mn atom ratio and aging time on catalyst activity and structure were investigated.The results showed that the catalyst with the Ni/Mn atom ratio of 0.4 and the aging time of 12 h（defined as NiO_x-MnO₂-0.4-12）hadthe best activity.o-Xylene was oxidized to carbon dioxide and water at 200°C,which is10°C lower than that of OMS-2 catalyst.Especially,the temperature of T₂₀（the temperature when the carbon dioxide yield is 20%）of NiO_x-MnO₂-0.4-12 is 21°C lower than that of the OMS-2 catalyst.XRD tests demonstrated that the Ni species were highly dispersed in the OMS-2 catalyst.BET results showed that the specific surface area of the OMS-2 increased from 28.12m²/g to 118.03 m²/g.According to the XPS test,the nickel oxide in the catalyst consists of Ni²⁺and Ni³⁺,and the contents of Mn³⁺and surface oxygen species were increased.wereH₂-TPR,TPR-TPOand O₂-TPDtests show that the incorporation of NiOx was beneficial for the improvement of the mobility of lattice oxygen and reoxidation capacity of the catalyst.The oxygen species was more easily released in NiO_x-MnO₂-0.4-12.CO₂-TPD showed CO₂is not easy to be adsorbed on NiO_x-MnO₂-0.4-12.In situ infrared diffuse reflectance infrared spectroscopy（In Situ DRIFTS）revealed that the oxidation ability of lattice oxygen in NiO_x-MnO₂-0.4-12was enhanced,which can oxidized o-xylene into maleate at 180°C.（2）A series of Ag/NiO_x-MnO₂-0.4-12 catalyst were prepared by deposition precipitation method by adding Ag on the Ni O_x-MnO₂-0.4-12 catalyst.The influences of Ag species quality percentag on catalyst activity and structure were investigated.The results showed that the catalyst with Ag species quality percentag of 0.05（defined as 5%Ag/NiO_x-MnO₂-0.4-12）had the best activity.the temperature of T₂₀0 of 5%Ag/NiO_x-MnO₂-0.4-12 is 72°C,which is 73°C lower than that of the OMS-2 catalyst.o-Xylene was oxidized to carbon dioxide and water at 190°C,which is 20°C lower than that of OMS-2 catalyst.XRD and XPS test showed that the Ag species in the catalyst consists ofAg⁺and Ag⁰ and they were highly dispersed in NiO_x-MnO₂-0.4-12 catalyst.H₂-TPR,TPR-TPO and O₂-TPD showed that the incorporation of Ag species was beneficial for the improvement of the mobility of lattice oxygen and reoxidation capacity of the catalyst.The oxygen species was more easily released in 5%Ag/NiO_x-MnO₂-0.4-12.In Situ DRIFTS revealed that the oxidation ability of lattice oxygen in 5%Ag/NiO_x-MnO₂-0.4-12 was enhanced,which can oxidized o-xylene into maleic acid salts and small molecules of carboxylic acid salts at 150°C.After introduction of molecular oxygen,maleic acid and small molecules of carboxylates quickly decompose into carbon dioxide and water.The results of activation energy calculation showed that the NiO_x-MnO₂-0.4-12and 5%Ag/NiO_x-MnO₂-0.4-12 catalysts have lower activation energy.The stability test showed that NiO_x-MnO₂-0.4-12 and 5%Ag/Ni O_x-MnO₂-0.4-12 catalyst continued to react 60h at the temperature of complete catalytic oxidation of o-xylene,and the activity remained almost unchanged.In the water vapor resistance test,two catalysts were passed through 2.6%steam at 190°C.The results showed that the catalytic activity of NiO_x-MnO₂-0.4-12 decreased by 20%,and the catalytic activity of5%Ag/NiO_x-MnO₂-0.4-12 decreased by 10%.After the water was stopped,the two catalysts were restored to their original activity.To sum up,doping Ni and Ag species in the OMS-2 catalyst are beneficial to improve the catalytic activity of the catalyst.In order to achieve the purpose of treating benzene series pollutants at low temperature.