Experimental Study On The Catalytic Combustion Of Diesel Particulate Matter With Ce_xMn_1-xO₂

Diesel engines are more widely used than gasoline engines for better powerful performance,fuel economy and work stability.However,the emission of particulate matter（PM）from diesel engine has a higher demand for exhaust purification technology.Catalytic oxidation for diesel particulate matter is an efficient,oriented and great perspective purification technology.Compared with the complex exhaust aftertreatments system,catalysts are cheap,efficient and have selective catalytic oxidation and reduction so that it can be promoted and applied extensively.It is also an issue for domestic and foreign scholars in relevant and interdisciplinary field.In this paper,rare earth based catalysts with fluorite crystal phase and structure and its compound oxides supported by embedded method were synthesised.A series researches of catalytic activity and mechanism on the catalyzing oxidation of diesel particulate matter were carried out,the specific research works are as follows:Three groups of CeO₂ with different micro-structure were produced by forward and reverse precipitation method with different process.The surface micro-topography research shows,the reverse precipitation method which was coordinated with absolute ethyl alcohol bring CeO₂ a more dispersed surface structure.The pores on its surface are vast and deep.The subgrain dimensions of CeO₂ were 20nm、11nm and 8nm.They had same oxygen species,but the activity temperature of surface lattice oxygen reduced when the subgrain dimensions decreased.At the same time,the fluidity of surface lattice oxygen increased,so did the concentration of surface lattice oxygen.The addition of CeO₂ promotes the oxidation of transitional precursor of soot.Compared with the process without CeO₂,the ignition temperature and the peak mass loss rate temperature decreased.CeO₂ will perform a better catalytic activity for PM when it has smaller subgrain dimensions and greater BET surface areas.Five groups of Ce_xMn_1-xO₂（x=1.0、0.9、0.7、0.5 and 0.3）catalysts were synthesized by complex combustion method with citric acid.Results showed that with the embedded support on Mn,there was little change on crystal structure of CeO₂.Mn has negtive effect for the subgrain dimensions of Ce_xMn_1-xO₂ catalysts,however it has a promotion for the BET surface areas.The concentration of Mn also promote the electron transition between energy levels in sublayer electron rail of Ce 3d.Ce_xMn_1-xO₂ catalysts performed a best ability of electron transition when the parameter x was 0.9,however,with a increasing the concentration of Mn,the electron transition between energy levels in sublayer electron rail of Ce 3d decreased.But the surface lattice oxygen and oxygen vacancy of catalysts increased.Ce-ion on the surface of catalysts are exist by Ce4+.In this way,the oxidation ability of catalysts are enhanced.Ce_0.5Mn_0.5O₂ has performed a best activity on diesel particulate matter.Therefore,CeO₂ supported on Mn promote the particulate matter oxidation substantially.Ce_0.5Mn_0.5O₂ catalyst was chose for coating sample.And then the impact of catalysts solid content and coating methods on the pressure drop of DPF were explored.Result shows that the coating method of vacuum and negative pressure has little impact on the pressure drop of DPF.Three groups of pressure drop characteristics of DPF loading on particulate matter indicate that when the solid content is 50 g and the upload capacity is 42g/L,the catalysts will have a little impact on the pressure drop of DPF and have a better activity.After particulate matter loaded on 10 h,the pressure drop increased from 2.5kPa to 7.22 kPa.The experiment of off-line regeneration of DPF showed,the ignition temperature of PM reduced remarkably with catalyst.