Study On 3DOM Ti-Based Oxide Catalysts For The Simultaneous Removal Of PM And NOx Emitted From Diesel Engines

Diesel engines are widely used in automobile,ship,heavy truck,construction machinery and other fields because of their good power,economy and durability.However,diesel engine not only saves fuel and increases power,but also results in high emissions of nitrogen oxide（NOx）and soot particles（soot）,which brings serious harm to human health and living environment.Therefore,reducing and eliminating the emission of nitrogen oxides and soot particles in diesel engine exhaust is the primary task of diesel engine exhaust catalytic purification,and the research in this area has important theoretical and practical significances.This dissertation is mainly devoted to the research of catalysts for simultaneous purification and elimination of nitrogen oxides and soot particles in diesel engine exhaust,so as to overcome the disadvantages of complex process flow and large system volume caused by the combination of particle filter（CDPF）and selective catalytic reduction（SCR）or nitrogen oxide storage reduction（NSR）technology in traditional exhaust after-treatment technology.The unique three-dimensional ordered macroporous structure（3DOM）of the as-prepared catalysts can increase the contact area of the reaction and improve the transmission efficiency of soot particle and gas molecules.Adding NH₃ to the reaction atmosphere can solve the problem of insufficient reducing components under lean burn conditions.In this thesis work,several series of titanium-based oxide catalysts including CeMOδ/3DOM ZrTiO₄（M=V,Mn,Fe,Co,Ni,Cu,W）,Fe_xMn_1-xOδ/3DOM ZrTiO₄,W_xCeMn Oδ/3DOM ZrTiO₄ and CeMn Oδ/3DOM Ti_1-xW_xO_y were prepared and used for catalytic elimination of nitrogen oxides and soot particles in diesel exhaust.A series of characterization techniques such as XRD,SEM,TEM,BET,XPS,H₂-TPR,NH₃-TPD,In-situ DRIFTS were used to analyze the structure and physicochemical properties of the catalysts,and the possible mechanism of simultaneous elimination reaction was proposed.The main conclusions are as follows:（1）A series of CeMO_δ/3DOM ZrTiO₄（M=V,Mn,Fe,Co,Ni,Cu,W）catalysts were prepared by colloidal crystal templating method and incipient-wetness impregnation method.The unique three-dimensional ordered macroporous structure of the catalyst can improve the effective contact area between the catalysts and soot particles and reduce the transport resistance.The simultaneous elimination performance of catalysts varies with the supported transition metal.For the reaction of de Soot,the peak combustion temperature of soot is ranked from low to high as follows:CeMnO_δ/3DOM ZrTiO₄<CeCoO_δ/3DOM ZrTiO₄<CeCu Oδ/3DOM ZrTiO₄<CeFeO_δ/3DOM ZrTiO₄<CeNiO_δ/3DOM ZrTiO₄<CeVO_δ/3DOM ZrTiO₄<CeWO_δ/3DOM ZrTiO₄;for the reaction of de NOx,the maximum conversion rate of NO is ranked from high to low as follows:CeWO_δ/3DOM ZrTiO₄﹥CeVO_δ/3DOM ZrTiO₄﹥CeMnO_δ/3DOM ZrTiO₄﹥CeCuO_δ/3DOM ZrTiO₄﹥CeNiO_δ/3DOM ZrTiO₄﹥CeCoO_δ/3DOM ZrTiO₄。（2）The series of Fe_xMn_1-xOδ/3DOM ZrTiO₄catalysts were prepared by colloidal crystal templating method and incipient-wetness impregnation method.The three-dimensional ordered macroporous structures of the catalysts and the electron modulation action of Fe and Mn jointly improve the activity of the catalysts.When the ratio of Fe to Mn is 1:1,Fe_0.5Mn_0.5Oδ/3DOM ZrTiO₄ catalyst displayed the best performance for simultaneous elimination,the peak combustion temperature of soot is419°C,and the temperature window of 80%NO conversion was 153～320°C.The interaction between Fe and Mn makes the Fe_0.5Mn_0.5Oδ/3DOM ZrTiO₄catalyst have the highest Fe²⁺/Fe³⁺,Mn⁴⁺/Mn³⁺,O_α/O_βand surface acid amount.In-situ DRIFTS characterization results show that Fe_0.5Mn_0.5Oδ/3DOM ZrTiO₄ catalysts react mainly through L-H mechanism and E-R mechanism to complete the catalytic elimination of NOx.（3）The series of W_xCeMnO_δ/3DOM ZrTiO₄ catalysts were prepared by colloidal crystal templating method and incipient-wetness impregnation method.Among them,W₁CeMnO_δ/3DOM ZrTiO₄ catalyst showed good simultaneous elimination performance.The catalyst exhibited more than 90%NO conversion in the temperature window of 250～396°C,and still has 52%NO conversion at the peak temperature of soot combustion.The results of characterization analysis show that W doping can increase the content of Ce³⁺on the surface of the catalyst,resulting in more oxygen vacancies and acid sites,so as to improve the removal efficiency of soot and NO.Theoretical analysis and in-situ DRIFTS characterization results show that the catalytic elimination of soot and nitrogen oxides over the W₁CeMnO_δ/3DOM ZrTiO₄ catalyst mainly follows active oxygen mechanism,NO₂-assisted mechanism,L-H mechanism and E-R mechanism.（4）The series of CeMnO_δ/3DOM Ti_1-xW_xO_y catalysts were prepared by colloidal crystal templating method and incipient-wetness impregnation method.The catalytic purification performance of the series catalysts for PM and NOx was studied by adjusting the ratio of Ti and W in the support.The results show that the simultaneous elimination performances of CeMn Oδ/3DOM Ti_1-xW_xO_y catalysts are affected by the content of W in the support.When the ratio of Ti to W is 7:3,the peak temperature of soot combustion is 488°C,and the catalyst has the maximum NO conversion rate of99.2%,the temperature window for NO conversion above 90%is 216～377°C,the addition of W also greatly improves the selectivity of N₂.The results of theoretical analysis and in-situ DRIFTS characterization show that the soot oxidation reaction over CeMn Oδ/3DOM Ti_1-xW_xO_y catalyst mainly goes through active oxygen mechanism and NO₂-assisted mechanism,while NO reduction reaction mainly follows L-H mechanism and E-R mechanism.