Study On Catalytic Combustion Of Soot With Manganese Oxide Supported On Ag-based Catalyst

Compared with gasoline engines,diesel engines have the advantages of high power,durability,and good economic performance.However,the emissions of solid particulate matter（PM,mainly―soot‖）and nitrogen oxides（NO_X,NO+NO₂）in diesel exhaust gas are very high.Which causes serious environmental and health problems.In order to reduce the emission of solid particles and nitrogen oxides,diesel particulate filter（DPF）is the most effective and widely used PM control post-processing technology.The direct oxidation of soot on non-catalyzed DPF requires high temperatures around 600°C,but diesel exhaust temperatures are between 175-400°C.How to eliminate carbon particles and nitrogen oxides in diesel exhaust at the same time is an extremely important direction in the field of catalytic and environmental protection research.Currently,catalysts that have been used in the oxidation of soot include noble metals,alkali metals,alkaline earth metals,and rare earth metal oxides.Ag-based catalysts have high low-temperature oxidation activity.Manganese oxides have high activity and are often used as catalytic oxidation materials.However,manganese oxide-supported Ag-based catalysts for catalytic oxidation have rarely been reported.In this paper,the manganese oxide catalysts were prepared by hydrothermal method.Ag-catalysts were prepared by impregnation method and redox method.The co-elimination properties of soot and NO_X were investigated.The main research contents are as follows:1.The oxidative properties of three different crystal phases ofα-,γ-andδ-MnO₂ were prepared by the hydrothermal synthesis method.The supported Ag-based catalysts were prepared by impregnation and redox methods.The oxidation performance of the catalyst in soot oxidation was investigated.The Ag catalysts supported on MnO₂ with different crystalline phases have been found to have good catalytic performance for soot combustion,andδ-MnO₂showed the best performance for soot with a Tp of 315°C.The activity of theα-MnO₂ andδ-MnO₂ catalysts was not increased much after the Ag loading,and the Tp over Ag/γ-MnO₂ supported catalyst reduced about 60°C.2.α-Mn₂O₃ with different morphology were prepared by the hydrothermal synthesis method,and the supported Ag-based catalysts were prepared by redox method.The effects of carrier morphology,redox properties and surface oxygen,on the combustion properties of soot were investigated.Theα-Mn₂O₃-C catalyst has the best activity with the Tp is 330°C and the window temperature is 131°C at oxygen atmosphere.It was found that the manganese oxide supported Ag catalyst with flower shape greatly improved the soot combustion activity.The effect of Ag content on the structure and properties of the catalyst was investigated.It was found that when the Ag loading reached 10 atom%,Ag and Mn showed the strongest effect and the best activity.The Tp about 300°C in the oxygen atmosphere and the Tp below 330°C were obtained.In catalytic circle test,the manganese oxides showed stable catalytic activity for soot oxidation.