Research On The Design Of Active And Stable CO Oxidation Catalysts Using The Interaction Between Metal And Supports

Currently,new energy technologies are booming,but oil-based internal combustion engines will dominate for about 25 to 30 years,and there is still important value for further research.Due to the continuous advancement of engine technology,the waste heat generated by the combustion of internal combustion engines is reduced,which reduces the temperature of motor vehicle exhaust gas,resulting in the future operating temperature of the vehicle exhaust gas treatment catalyst being lowered by about 100°C than the current.At the same time,in recent years,our country’s motor vehicle pollutant emission standards have been continuously improved,putting new requirements on the design of exhaust gas treatment catalysts.Since the popularization of vehicle exhaust gas treatment catalysts in the 1970s,due to the inactivity of the catalyst at low temperatures,exhaust pollutants emissions mainly occur during the cold start of vehicles,accounting for more than 90%of the total emissions.Therefore,on the basis of controllable cost,there is an urgent market demand for the development of low-temperature and high-activity exhaust gas treatment catalysts.In addition,the engine will generate high temperature or extremely high temperature locally under high load conditions,which requires the exhaust gas catalyst to have excellent high temperature stability at the same time.Therefore,the development of new catalysts for vehicle exhaust treatment with high activity at low temperature and high stability at high temperature has become a research hotspot in recent years.From the perspective of catalyst design,low-temperature active catalytic active sites are often difficult to stabilize at high temperatures,and high temperature stable catalytic active sites tend to have low activity at low temperature.The two are contradictory and difficult to balance.In practical applications,it is usually solved by increasing the amount of precious metals（Pt,Rh,Pd,etc.）,but the cost is relatively high.This dissertation selects one of the most important reactions in exhaust gas treatment（CO oxidation reaction）,and adopts the following research ideas to promote the solution of this problem:First,the catalyst is stabilized by the strong interaction between the highly dispersed precious metal Pt and the support Ce O₂,to ensure the high temperature stability of the catalyst;after that,on this basis,the second component Ag with higher low temperature activity is added to improve the low temperature activity of the catalyst.In this way,a CO oxidation catalyst with both activity and stability can be preliminarily designed.The specific research results are as follows:1.The reaction test results show that the Ag/Ce O₂ catalyst has good low-temperature carbon monoxide oxidation activity.The reaction follows the Eley-Rideal mechanism,that is,O₂ is adsorbed on the oxygen vacancies near Ag on the catalyst surface and reacts directly with gaseous CO（CO does not need to be adsorbed on Ag site）to form CO₂.However,the interaction between the metal and the support in Ag/Ce O₂ is weak.After high temperature treatment,the Ag particles agglomerate and grow,and the Ag-O bond of the reactive center decreases.In addition,the higher the crystallinity of the support leads to a decrease in specific surface area and a decrease in defects on the surface of the catalyst.Causes low temperature activity to decrease.2.The Ag/Pt-Ce O₂ catalyst has good low-temperature CO oxidation activity and high-temperature stability.The test results confirmed that there is a strong metal support interaction（SMSI）between Pt and Ce O2,and the formed Pt-O-Ce bond can stabilize Ce O₂at high temperatures.On Pt-Ce O₂,the reaction follows the Langmuir-Hin Shelwood mechanism,where CO and O₂ compete for adsorption on Pt sites.The addition of Ag formed a highly reactive Ag-O bond,which changed the CO adsorption process on Pt-Ce O₂.Different from Ag/Ce O₂,the reaction on Ag/Pt-Ce O₂ follows the Mars-van Krevelen mechanism.CO is adsorbed on the Pt sites on the catalyst surface and reacts with O₂ adsorbed by oxygen vacancies near Pt to form CO₂,which reduces the energy barrier of the reaction and enables the catalyst to have CO oxidation activity at low temperatures.Different from the traditional approach to continuously improve the catalytic activity of noble metal sites,this paper uses the SMSI between the highly dispersed Pt and the support to stabilize the catalyst,and then introduces the transition metal Ag to improve the low-temperature activity of the catalyst.The research strategy of this dissertation enables the catalyst to have both good low-temperature activity and high-temperature stability,reduces the amount of precious metals and reduces the cost.It also provides a new idea and basis for the development of stable and active new oxidation catalysts.