Study On The Structure-Function Relationship In Catalyzing C1 Conversion And Ammonia Decomposition Reaction Over Rare Earth Oxide Based Catalysts

As the country with the richest reserves of rare earths,the development of such an important strategic resource is vital to China.Rare earth based catalysts have been widely used in many classical fields,but the development of rare earth catalytic materials is still significant for the energy and environment catalytic reactions.In this dissertation,except for CeO2 based catalytic materials with partial reduction,I also explorer other rare earth oxide based catalysts with cubic structures,such as Y2O3,Sm2O3 and so on.For supported catalysts,I will discuss the effect of the rare earth oxides themselves and their advantages in regulating the active metal state.Then,following the strategy of inverse catalytic interface construction,I study their role in stabilizing the catalyst structure and constructing high catalytic performance interfaces.Using various in situ/ex situ characterization techniques,I explore the state transition of rare earth oxide loaded metals,structural changes of the active interface and metal-rare earth oxide interactions.And the synthesized rare earth oxide based catalysts are applied in CO oxidation reactions,water-gas shift(WGS)reactions and ammonia decomposition reactions,all of which exhibited highly competitive catalytic performance.The mechanism and structure-function relationship are investigated through a combination of experimental and theoretical studies.This dissertation centers on the development of rare earth oxide based catalysts,which provides new ideas for the application potential of rare earth oxide based catalytic materials.The specific body of work in this dissertation is as follows:1.A dynamic study of the reversible transformation of the Ru species supported on CeO2.Abundant oxygen vacancies exist in the CeO2 surface,which can promote the dispersion and anchoring of the active metal.And the size change of the active metal leads to the change of electronic and geometric states at the metal-oxide interface,which in turn causes the difference in catalytic performance.In this work,Ru/CeO2 is pretreated in oxidation treatment(O2,air),inert atmosphere treatment(N2,Ar),and reduction treatment(H2,CO).The dynamic changes of Ru species states are examined by various characterizations.Ru single atoms and nanoclusters can achieve dynamic transitions by switching between oxidizing and reducing environments,indicating the strong sensitivity of Ru species supported on CeO2 to environmental changes.For CO oxidation reaction tests,the obvious activity differences of the catalysts after pretreatments fully illustrate the fact that Ru species have undergone dynamic transformations.The results of in situ DRIFTS under the reaction atmosphere determine that larger size Ru clusters are more active and CO adsorbed on the Run+ sites have higher reactivity.This work provides an important experience for a comprehensive understanding of Ru species state change behavior and the development of catalysts with excellent activity.2.Intrinsic surface oxygen vacancy in rare earth(Ⅲ)oxides for heterogeneous catalysis.While CeO2 has been widely discussed by researchers due to its partial reduction,the application of other rare earth(Ⅲ)oxides has been less studied.There is no systematic research and clear understanding of the role played by such material for catalytic reactions.In this work,we discover a new type of Ov that is an intrinsic part in the perfect crystalline surface,which is not related to the oxidation state change of cations.Such non-defect Ov stems from the irregular hexagonal sawtooth-shaped structure in the(111)plane of rare earth(Ⅲ)oxides(RE2O3).The neighbour RE3+ is coordinated with five O2-instead of the common six O2-coordination.Such unique Ov structure shows good performance in the ammonia decomposition reaction with surface Ru active sites.Between 2800 and 3500 mmol·gRu-1·min-1 of H2 formation rate is achieved at～1wt.%of Ru loading over Sm2O3,Y2O3 and Gd2O3 surface(GHSV=30,000 cm3·gcat-1·h-1),which is 3-30 times higher than reported values in the literature.The 5coordinated RE3+ directly adsorbs NH3 via RE-N bond,and helps keep Ru at metallic state to facilitate the N-H bond breaking.Our discovery of intrinsic Ov suggests great potential of RE2O3 in heterogeneous catalysis and other surface applications.3.Catalytically efficient Ni-NiOx-Y2O3 interface for medium temperature water-gas shift reaction.For rare earth oxides supported catalysts,a large number of bulk atoms often averages out the information of interfacial oxide atoms.The essential catalytic role of rare earth oxides is difficult to accurately understand.To address this difficulty,we propose a strategy to reduce the size of the oxide to increase its disorder to facilitate our understanding of rare earth oxides.In this work,the Ni9Y1Ox composite catalyst is prepared by ultrasonic spraying method and formed highly efficient Ni-NiOx-Y2O3 catalytic interface after WGS reaction.The interface structure was accurately identified by various characterizations such as transmission electron microscopy and in situ Raman.The catalytic performance tests show that the Ni-NiOx-Y2O3 interface achieving 140.6 μmolco gcat-1 s-1 rate at 300℃,which was 4 times to the existing literature reports.A combination of theory and ex/in situ experimental study suggests that Y2O3 helps H2O dissociation at the Ni-NiOx-Y2O3 interfaces,promoting this rate limiting step in the WGS reaction and facilitating the reaction with associative mechanism.The addition of Y2O3 restricting the growth of the Ni particles under the reduction conditions and forming the NiNiOx-Y2O3 interfacial sites under the WGS condition.Construction of such new interfacial structure for molecules activation holds great promise in many catalytic systems.