Study On The Synthesis And Properties Of Pt-Pd/CeO₂-SiO₂ Oxidation Catalyst

In the process of tail gas post-treatment of diesel vehicles,the improvement of NO2 content in exhaust has a key role: on the one hand,it can reduce the burning temperature of soot and effectively promote the DPD/CDPF passive regeneration efficiency and reduce the complexity of the exhaust system.On the other hand,When the NO2/NO=1,SCR catalyst can achieve rapid SCR reaction,greatly enhance its DeNOx performance at low temperature.In general,the content of NO2 in diesel exhaust is less than 10%,and NO conversion to NO2 is one of the key technology.Therefore,the study of NO oxidation catalyst is of great practical significance.In this paper,the synthesis process of the carrier materials of NO oxidation catalyst was studied.The NO oxidation performance of the catalyst prepared by loading noble metals was evaluated.On the basis of this,the CeO2-SiO2 composite oxide was modified by the transition metal elements.The main results are summarized as follows:In this paper,the preparation of new CeO2-SiO2 composite oxide carrier is mainly explored.The synthesis process of CeO2-SiO2 composite oxide is determined by various characterization methods studying its properties and redox performance.The best composite oxide carrier was prepared by the way.Then,Pt-Pd/CeO2-SiO2 double noble metal catalyst was prepared by impregnation method,and the NO oxidation performance of fresh and aged samples was studied under different reaction atmosphere.Finally,The CeO2-SiO2 composite oxide was modified by transition metal element,and the Pt-Pd/Ce-Si-X catalyst was prepared by impregnation method,and the NO oxidation performance was studied under different reaction atmosphere.Through the above detailed study to draw the following conclusions:(1)The influence factors such as the mass ratio of CeO2/SiO2,the reaction temperature,the reaction time,the calcination temperature and the stirring method were analyzed in detail by N2-desorption,X-ray diffraction,transmission electron microscopy,X-ray photoelectron spectroscopy and temperature programmed reduction.CeO2-SiO2 composite oxide with excellent redox performance was synthesized.The composite oxide belongs to the typical strawberry-like structure,and there is a chemical bond interaction between CeO2 and SiO2,which effectively inhibits the growth of CeO2 grains,increases the lattice defects,effectively improvesthe proportion of the Ce3 +in the CeO2,reduces the lattice oxygen reduction temperature from 840? to 622?.(2)The noble metals was loaded on the synthesized CeO2-SiO2 composite oxide and its NO oxidation performance was studied.For the fresh catalyst,in NO+O2+N2 reaction atmosphere,compared with the Pt-Pd/La-Al2O3,the NO low temperature oxidation activity of Pt-Pd/CeO2-SiO2 was better,and the temperature window of NO2/NOx ? 50% was wider.However,when CO and H2 O were added in the reaction atmosphere,the activity of the catalyst decreasednarrowly,indicating that CO and H2 O on the catalyst NO oxidation process has anobvious inhibitory effect.The inhibitory effect of CO and H2 O on the NO oxidation of Pt-Pd/CeO2-SiO2 catalyst was obviously weakened after 780?/10 h high temperature aging,and the activity of low temperature was improved and the temperature window was broadened.But compared with Pt-Pd/La-Al2O3,the inhibitory effect of CO and H2 O on the catalyst NO oxidation was still evident.(3)The CeO2-SiO2 composite oxide was modified by Mn,Ni,Cr,Cu,Fe transition metal elements,and found that the interaction between Mn and Ce was the strongest,which effectively inhibited the growth of CeO2 grains,So that the lattice oxygen reduction temperature of CeO2 was reduced to 494 °C.The NO oxidation performance of Ce-Si-Mn composite oxide was investigated,and found that the material had excellent low temperature NO oxidation activity and wide temperature window.On the basis of this,Pt-Pd/Ce-Si-Mn catalyst was prepared.Although the activity of low temperature was decreased,the inhibitory effect of CO and H2 O on NO oxidation was weakened and the temperature window was widened.However,after high temperature aging,the NO oxidation performance of the catalyst deteriorated rapidly,and the inhibitory effect of CO and H2 O had become more and more significant.