Study On "Structure-activity Relationship" Of Supported Platinum-based Catalysts For CO Catalytic Oxidation

Carbon dioxide,a very important pollutant for environment,is mainly generated by incomplete combustion of fossil fuels and directly discharged into the atmosphere without any treatment.Environmental CO pollution removing relying on catalytic oxidation is now an important direction of the pollution controlling.Design and synthesize supported catalysts for CO oxidation with high activity and stability is now a challenging study for researchers.At present,studying the"structure-activity relationship"of catalysts is a significant method in catalysis research,for it is an important guide in design excellent catalysts.Rare earth oxides or hydroxides was the main supports for Pt based catalyst in this thesis to reveal the"structure-activity relationship"in the catalytic CO oxidation by studying the morphology effect,phase effect and chemical environment effect of the Pt metal center in the supported catalyst.The research contents of this thesis are as follows:（1）Pt species were introduced into La supports with different phases to construct supported Pt /LaO_x（OH）_y catalysts for the CO oxidation reaction.With the help of activity test and a series of characterizations,we found that Pt displayed the highest activity when supported on basic lanthanum oxide LaOOH support with the Pt -O₄ sites,due to its lowest oxidation state than Pt on the La₂O₃ and the La（OH）₃ supports.In addition,the LaOOH supports provided more active oxygen for improving the CO oxidation activity.But the further study using TG-MS showed us that the activity of the catalysts was rapidly decreased,with the inevitable generated La₂O₂CO₃ during synthesis and catalytic process could hinder the desorption of CO₂.（2）We introduced Pt nanoparticles（PtNPs）into ultrathin nanosheets Y₂O₃-Na Cl synthesized by Na Cl template,and as a comparation,a Na Cl-free Y₂O₃ directly calcinated at the same temperature was prepared.With the help of CO oxidation activity test and a series of characterizations,we found that PtNPs can be equally dispersed on the Y₂O₃-Na Cl support with smaller size;however,the Pt nanoparticles was agglomerate in large quantities with an extremely large size,when supported on the Na Cl-free Y₂O₃.We can clearly prove the above point by XAS and TEM technology.We further found that Pt /Y₂O₃-Na Cl is easily reduced to 0 valence and exposed more Pt active sites to improve CO oxidation by the test of XPS and in situ DRIFTS while the Na Cl-free one was on the contrary.（3）A traditional Pt /CeO₂ catalyst was synthesized by impregnation method for CO oxidation.Different pretreatment condition was executed before CO oxidation to explore the effect of the species change of Pt on CeO₂ support.We found that Pt with the metallic state on the CeO₂ support manifestation the highest CO oxidation activity due to a series of characterizations,however,Pt in this state is not stable to oxidize to Pt -O₄ species that can exist stably under CO oxidation conditions by O₂ in the reaction atmosphere.With the help of the near situ XAS test,we identified the most active CO oxidation site as metallic Pt ,and the Pt -O₄ site was the optimal active site for long-term CO oxidation.In summary,we had explored the two basic factors of the catalyst（support,metal center）from different directions through the study of the above three research systems:the effect of the phase change of the support on the oxidation of CO has been study in the first work to certify the deactivation for CO oxidation of the generation of La₂O₂CO₃;the effect of the support morphology on the CO oxidation reaction has been study in the second work to demonstrate the dispersibility for PtNPs of Y₂O₃ nanosheet and the effect of the chemical environment of the Pt metal center on the CO oxidation reaction has been study in the third system to ascertain the species of metallic Pt for CO oxidation.We hope that the above research can provide some guidance for the research of catalysts from the aspects of supports synthesis and phase change and CO oxidation active site identification and design synthesis.