| With the rapid development of automotive industry,vehicle exhaust emissions cause severe environment problems.It is urgent and important to eliminate those exhaust pollutants,including CO,HCs and NOx.Three-way catalysts?TWCs?have shown high efficiency and wide applications in elimination of above-mentioned vehicle exhaust pollutants.Precious metals?Pt,Rh,and Pd?are widely utilized as traditional TWCs due to their high reaction activity.However,a combination of high price,limited amount,poor stability and particles agglomeration under high temperature conditions limit their further application.ABO3 type perovskite material has been investigated due to its low cost and outstanding catalytic activity for NO and CO oxidation.However,the poor hydrothermal aging resistance of perovskite under harsh engine emission conditions seriously limited its practical application.Hence,a novel catalyst with a better catalytic performance and hydrothermal aging resistance is desired to meet the increasing strictly legislation and lower the cost.Mullite oxide have attracted much attention due to their favourable NO oxidation performance and strong stability at high temperature.Mullite oxide SmMn2O5?SMO?was synthesized through a co-precipitation method and its three-way catalytic activity was evaluated and compared to that of perovskite LaCoO3?LCO?.SmMn2O5 showed a better reaction activity as well as a higher catalytic activity and stronger hydrothermal resistance.Following material characterizations including XRD,BET,SEM,XPS,H2-TPR,O2-TPD,and CO+O2 pulse were undertaken to gain insight into the origin of the three-way catalytic activity,physical chemistry properties and reaction mechanism of the catalysts.The main contents of this dissertation are listed below:?1?The CO oxidation and three-way catalytic performance of mullite oxide SmMn2O5 were investigated and compared to that of perovskite catalyst LaCoO3. The results indicated that mullite oxide showed better CO oxidation performance and higher three-way catalytic activity than LaCoO3.Its CO oxidation performance reaches that of noble metal catalyst 2%Pt coated on Al2O3.The H2-TPR,O2-TPD and CO+O2 pulse tests verified that mullite oxide SmMn2O5 catalyst obtained a better reducibility,stronger migration ability of oxygen species and larger oxygen storage capacity than LaCoO3.That is the key factor for higher catalytic activity for mullite oxide SmMn2O5.?2?The oxide catalysts were hydrothermal aged at 850 o C and 1050 o C to evaluate their three-way catalytic performance.The result indicted that mullite oxide SmMn2O5 showed a superior hydrothermal aging resistance than LaCoO3.The XRD,SEM and BET analysis of hydrothermal aged catalysts showed that hydrothermal aging treatment didn't change the structure of catalyst samples, while leading to grain growth and decrease of the specific surface area and catalytic performance.Again,the mullite showed better three-way catalytic activity than perovskite,suggesting its stronger hydrothermal aging resistance.?3?A catalyst evaluate device was designed and built to appraise the catalytic performance of coating carrier.The result indicated that the device exhibits the structure stability and air tight property,which can meet our requirements during the detection of three-way catalytic activity.?4?After confecting the formula of coating carrier and coating Cordierite carrier,the catalytic performance of coating carrier was rested and compared with commercial catalyst with the evaluation system described above.The results show that the coating carrier could realize the purification of automobile exhaust within a reasonable transformation temperature window,although the performance of coating carrier in in ferior to commercial carrier,it provides theoretical basis and data support for the transition of laboratory research to commericial applications. |
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