Study On Perovskite Catalyst For Simultaneously Removing NO And Soot From Diesel Engine Exhaust

Four way catalytic technology is an important way to eliminate the exhaust pollution of diesel engines.In this work,a series of LaCoO₃ perovskite composite metal oxide as the catalysts were synthetised,by doping the perovskite at the A site.It is shown that Sr doping is beneficial to improve the catalytic activity for simultaneous removal of NO and Soot.When the Sr doping amount is 0.1,this catalyst could possess the best low-temperature catalytic activity.At GHSV=10000h^-1,the NO conversion could reach 64.2%and the T_m is 340.0°C.XRD and SEM show that the doping of different Sr content can still maintain the complete perovskite structure.This catalyst with the Sr doping amount of 0.1,would keep the best crystallinity,particle size and dispersion,leading to increasing gas-solid-solid reaction contact site.The H₂-TPR and NO/O₂-TPD show that Sr-doped LaCoO₃ significantly improves the low-temperature redox performance,and increased the adsorption sites and storage performance?OSC?of NO and O₂.XPS results show that Sr doping upsets the charge balance of catalyst,resulting in certain lattice defects in the catalyst.These defects are conducive to the formation of surface adsorbed oxygen and oxygen vacancies.Both good stabilities for their structure and performance were exhibited for this catalyst La_0.9Sr_0.1CoO₃.When different metals?Fe,Mn,Cu and Mg?doped LaCoO₃ at B site,the Fe doping could obtain the best low-temperature catalytic activity.At GHSV of 15000h^-1,the maximum NO conversion reached 21.6%,and the T_m was 385.5°C.The order of activity is:Fe>Mn>Cu>Mg.With the doping of different metals,we proved that the complete perovskite structure can still be maintained by the XRD,and both the low-temperature reduction performance and surface adsorbed oxygen activity have been improved to a certain extent,especially for the Fe,Mn,and Cu doping.Based on the optimal B-site doped metal Fe,the effect of different doping amounts on the structure and performance was further explored.It was found that the catalyst with Fe doping amount of 0.2,could obtain the best low-temperature catalytic activity,with a maximum NO conversion of 21.6%and a T_m of 385.5°C.The SEM show that suitable Fe doping amount could improve the catalyst particle dispersion,and reduce particle agglomeration and stickiness,causing in increasing contact sites for heterogeneous reactions.XPS shows that different Fe doping can increase the charge unsaturation of catalyst,which is beneficial to enhance the surface adsorbed oxygen and oxygen vacancy content.Thus,LaCo_0.8Fe_0.2O₃ with the largest surface adsorbed oxygen,could further improve its low-temperature catalytic activity.The order of the low-temperature reduction ability with the Fe doping amount is as follows:LaCo_0.8Fe_0.2O₃>LaCo_0.9Fe_0.1O₃>LaCo_0.7Fe_0.3O₃?LaCo_0.6Fe_0.4O₃>LaCoO₃.Based on the best A-site doped catalyst La_0.9Sr_0.1CoO₃,we further studied the effect of simultaneous doping of Sr and Fe at A and B sites on the structure and performance of catalyst,the results show that La_0.9Sr_0.1Co_0.7Fe_0.3O₃ has the best low-temperature catalytic activity.When GHSV=15000 h^-1,the maximum NO conversion is 32.5%,and T_m and T_f are only 368.5°C and430.5°C.Through the systematic characterization,after the Sr and Fe doped with LaCoO₃,the catalyst can still maintain the complete perovskite structure.When the Fe doping amount is 0.3,the catalyst has the best crystallinity,particle size and dispersibility,excessive Fe amount will easily lead to increased perovskite crystallinity and particle stickiness.The H₂-TPR and NO-TPD show that strong interactions between Co and Fe ions with the change of Fe doping amount can significantly improve the low-temperature reduction performance,surface oxygen species activity and NO_x adsorption sites and performance.XPS results show that Fe doping can increase the content of surface adsorbed oxygen and(Co⁴⁺)on the catalyst surface,it is essential to improve the catalytic oxidation ability.La_0.9Sr_0.1Co_0.7Fe_0.3O₃ catalyst can keep the stable catalyst structure and redox performance after the continuous operation,indicating that it has excellent stability and durability.In this work the formulations of optimal perovskite catalyst were selected by a series of experiments.We investigated the effects of different coating materials,carriers,and coating methods on the NO_x removal activity of the catalyst.The results show that the structure of perovskite catalyst can still be prepared in scale-up experiments.When the powder slurry-nitrate dope method is used to coat the catalyst powder,the particles have good dispersibility on the ceramic support.Different coating materials and carriers could have a greater influence on catalytic NO removal activity,CeO₂ is better than?-Al₂O₃,DOC?Diesel Oxidation Catalyst?is better than DPF?Diesel Particulate Filter?.Different catalyst powder coating methods also have a greater impact on the activity,the order of the activities by using different coating methods is:powder slurry-nitrate stock solution method>nitrate stock solution method>powder slurry method.When the La_0.9Sr_0.1CoO₃ catalyst powder was coated by the powder slurry-nitrate solution method,the NO conversion was 12.5%at 270.0°C,and the NO conversion was further increased with increasing temperature,and was 390.0°C the highest NO conversion could reach 36.1%.There exists an optimal coating amount of catalyst powder,the excessive coating of catalyst powder may cause agglomeration.When the powder slurry-nitrate solution method is used for the first time to coat La_0.9Sr_0.1Co_0.7Fe_0.3O₃,its catalytic NO activity is the highest,the NO conversion reach 22.4%at 420.0°C.Further study of the catalytic performance for the oxidation of soot,show that La_0.9Sr_0.1Co_0.7Fe_0.3O₃ could simultaneously contain good catalytic activity for soot oxidation,with T_m and T_f of 341.0°C and 422.3°C.