Preparation Of Manganese-based Oxides Catalysts With Different Crystal Types By Hydrothermal Method And Their Catalytic Performance For Soot Combustion

Diesel engines are considered to be efficient and durable internal combustion engines,which have been widely used in medium and heavy vehicles and large machinery,such as road transport,ships,cranes and other fields.However,diesel engine emissions of pollutants,such as soot particles（PM）,nitrogen oxides（NOx）,hydrocarbons（HC）,carbon monoxide（CO）,especially for soot particles,will cause serious harm to the environment.Soot particles are not only the main source of PM2.5 in the urban atmosphere,but also can absorb a large number of carcinogens such as benzopyrene and nitro polycyclic aromatic hydrocarbons on the surface,which can enter the human body and cause respiratory diseases and seriously harm human health.At present,the removal of soot particles by catalytic purification technology is one of the most effective ways,and the development of highly active catalysts is the key factor to determine the wide application of this technology.Therefore,it is of great practical and environmental significance to design and develop highly efficient catalysts for soot combustion.In this thesis,Mn Oδ,K-OMS-2,Kx Mny Oδand Nax Mny Oδcatlaysts with different crystal forms were prepared by hydrothermal method,and the relationships between the physicochemical properties of catalysts and catalytic activity of soot combustion were studied by multiple characterization techniques.The main conclusions of this paper are as follows:（1）A series of Mn Oδcatalysts with layered structure were successfully prepared by simple hydrothermal method,and their catalytic performance of soot combustion was evaluated under different conditions.The results showed that Mn Oδ-t12 catalyst exhibited the best activity and stability for soot combustion due to its strongest reduction ability and the largest number of reactive oxygen species.The values of T₁₀,T₅₀ and T₉₀ were 274℃,321℃and 354℃,respectively.（2）A series of K-OMS-2 catalysts with tunnel structure were successfully prepared by hydrothermal method,and the catalytic performance of the prepared catalysts for soot combustion was investigated.The results showed that the K-OMS-2-t170 catalyst exhibited the best catalytic activity for soot combustion.The temperature values of T10,T50 and T90 were282℃,326℃and 359℃,respectively,and the selectivity of CO₂ was 98.6%.（3）Based on the content of the previous two chapters,K2Mn4O8 and K2-x Mn8O16 composite oxide catalysts with layered structure and tunnel structure were prepared by hydrothermal method,and the influence of the physicochemical properties of the catalysts on the catalytic performance for soot combustion were investigated.The results indicated thatthe tunnel structure Kx Mny Oδ-t110 catalyst has stronger NO oxidation capacity,more surface high-valence Mn⁴⁺ions(Mn⁴⁺/Mn³⁺=1.24)and reactive oxygen species(O_ads/O_lat=0.618)than that of layered K_xMn_yOδ-m₂₄ catalyst.The values of T₁₀,T₅₀ and T₉₀ were 269℃,314℃and 346℃,respectively.（4）Based on the content of the previous three chapters,a series of romanite Na2Mn5O10（Nax Mny Oδ）catalysts with 2×3 tunnel structure were prepared by hydrothermal method and applied to the soot combustion.Among the as-prepared catalysts,Na1Mny Oδ-120catalyst exhibited the best catalytic performance for soot combustion,and the values of T10,T50and T₉₀ were 281℃,317℃and 343℃,respectively,CO₂ selectivity is 96.1%.The existence of water vapor is beneficial to the soot catalytic combustion because of the formation of protonated substancesor the reduction of activation energy of reaction.Meanwhile,the possible reaction mechanism of as-prepared catalyst was proposed based on the characterization results.