Study On Preparation Of Pt Stabilied CuO/CeO₂ Catalysts And CO Oxidation Performance

Catalytic oxidation of CO,HC,and reduction of NO_X are the most important catalytic reactions in the emission reduction of motor vehicle exhaust.The U.S.Department of Energy had set a target for reducing emissions of motor vehicle,trying to develop a catalytic system that eliminates more than 90%of standard pollutants below150℃,which is about 100℃lower than the active temperature of current commercial vehicle catalysts,so that is called for the"150℃challenge".At the same time,our country’s motor vehicle emission standards have also been further improved,so the performance of tail gas treatment catalysts need to be further improved.In recent years,the development of a new generation of tail gas treatment catalysts have been a research focus.The temperature of the gas discharged from the engine outlet to the exhaust manifold is 800-900℃.After multi-stage treatment,the temperature of the exhaust gas discharged from the exhaust pipe outlet is about 30-120℃.In addition,most of the emission of motor vehicle exhaust pollutants occur during the"cold start"period.so a new generation of exhaust gas treatment catalysts must have both low temperature activity（<150℃）and high temperature stability（>800℃）.However,from the perspective of catalyst design,low-temperature active catalytic active centers are often unstable at high temperature,and high-temperature stable catalytic active centers are often inactive at low temperature.The two are contradictory that have always been a difficult to overcome as a bottleneck problem,so the problem is challenging.The thesis starts with the CO oxidation reaction and adopts the following research ideas to promote the overcoming of the above-mentioned bottleneck.First,utilizing the strong interaction between Pt and CeO₂ support（SMSI）to prepare high-temperature stable Pt/CeO₂catalyst.Next,loading low-temperature active Cu component on high-temperature stable Pt/CeO₂.The Cu component can obtain good high-temperature stability and maintain low-temperature activity at the same.The specific research results are as follows:（1）The high-temperature stable Al₂O₃ support contributes to the stability of the Cu active center.After calcination at 800℃,the Cu/Al₂O₃ catalyst still has a specific surface area of 130 m²·g^-1,Cu component is not sintered.The T₅₀ of the light-off curve is only about 50℃higher than the catalyst calcined at 400℃.It is proved that good high-temperature stability of the support is the key to ensure that the active center is not sintered under high temperature condition and guarantee the high-temperature stability of the catalyst.（2）The CeO₂ support is different from the Al₂O₃ support,as the most important oxide component in the exhaust catalyst,with poor high-temperature stability.After calcination at high temperature,the specific surface area of CuO/CeO₂ catalyst decreased from 55 m²·g^-1 to 6.1 m²·g^-1（calcined at 800℃）and 1.7 m²·g^-1（calcined at900℃）.In addition,Cu component is significantly sintered,the crystal grains increase to 34.7 nm（calcined at 800℃）and 38.9 nm（calcined at 900℃）.The T₅₀ of the light-off curve is about 110℃higher than the catalyst calcined at 400℃.Proved again that there is a weak metal-support interaction between Cu and CeO₂.CuO/CeO₂catalysts have good activity at low temperature but unstable at high temperature.The key to keeping Cu activity is to maintain the high-temperature stability of the CeO₂support.After calcination at 900℃,the specific surface area of the Pt/CeO₂ catalyst remains at 20.7 m²·g^-1,which has good high temperature stability.（3）Due to the strong metal-support interaction between Pt and CeO₂,the formation of Pt-O-Ce bonds during high-temperature calcination can make the Pt/CeO₂ catalyst stable at high temperature.After calcination at 900℃,the specific surface area of the Pt/CeO₂ catalyst remains at 20.7 m²·g^-1,which has good high temperature stability.The CuO/Pt-CeO₂ catalyst obtained by loading Cu on the Pt/CeO₂ catalyst can remain basically stable when calcined at 800℃(12.9 m²·g^-1),and the low-temperature activity has also been significantly improved.The T₅₀ of the light-off curve is about 290℃lower than the Pt/CeO₂ catalyst,and it is only about 25℃higher than CuO/Pt-CeO₂calcined at 400℃.Kinetic analysis and in-situ infrared characterization show that under high temperature conditions,the catalytic activity center is provided by Cu,while Pt only acts as a stabilizing catalyst.In summary,using strong metal-support interaction to promote high-temperature stability of the catalyst,and utilizing weak metal-support interaction to provide low temperature activity of the catalyst,the catalyst design strategy has been proven to be feasible and effective in this thesis.The thesis preliminarily designed CuO/Pt-CeO₂catalyst with good high-temperature stability and low-temperature activity,which provides new research idea and theoretical basis for the development of a new generation of exhaust gas treatment catalysts and other combustion catalysts.