Cerium-based Coordination Polymer Derived Bimetal Oxides And Their Catalytic Performance Study

Metal coordination polymers(CPs)or metal organic frameworks(MOFs)derived bimetallic oxides,as a class of porous crystalline materials,have a unique structure and a wide range of applications.Compared with CPs/MOFs-derived single-component metal oxides,bimetallic oxides have superior catalytic activity due to the synergistic effect of multiple components.At present,CPs/MOFs-based bimetal oxide composite catalysts can be obtained by calcination of bimetal CPs/MOFs.However,due to the different coordination capabilities and coordination behavior of different metal ions,how to ensure the effective synthesis of bimetal CPs/MOFs with controllable components is still one challenge.It is also possible to firstly prepare monometallic CPs/MOFs,and then further synthesize bimetallic oxides through post-processing strategies,however,the homogeneous nucleation of the second phase(metal oxide)needs to be carefully controlled and prevented.Therefore,searching suitable organic ligands and synthetic conditions to prepare bimetallic CPs/MOFs,and exploring novel and universal methods are conducive to the heterogeneous nucleation of second-phase metal oxides in CPs/MOFs or their derivatives.This is essential for the construction of MOFs-derived bimetal oxide composite catalysts.Based on this,this paper successfully synthesized a series of cerium-based coordination polymer(CPs/MOFs)derived bimetallic oxide,and explored the conditions that affect its morphology.At the same time,in order to explore the structure-performance relationship between cerium-based CPs/MOFs-derived bimetallic oxides,studies were carried out from the aspects of catalyst preparation,structure characterization,formation mechanism,and catalytic performance testing.1.Ce-Mn coordination polymer derived hierarchical/porous structured CeO₂-Mn O_xfor enhanced catalytic propertiesThe solvothermal method was used to successfully synthesize a bimetallic coordination polymer with adjustable composition,and further heat treatment to obtain a layered/porous structure CeO₂-Mn O_xcatalyst.Due to the unique layered/porous structure and the intimate contact between CeO₂and Mn O_x,CeO₂-Mn O_xcatalyst exhibits excellent catalytic performance in CO oxidation reaction and NH₃-SCR.In addition,the catalytic performance of CeO₂-Mn O_xcatalysts highly depends on the Mn/Ce ratio.A series of characterization results such as XPS,Raman and H₂-TPR show that when the ratio of Mn/Ce is 1,the CeO₂-Mn O_x(5:5)catalyst has a higher content of Ce³⁺,Mn⁴⁺and O_surf,which is the main reason why the catalytic performance is better than other components.The preparation method provides a simple and effective idea to synthesize CPs-derived metal oxides with a layered/porous structure,and can be extended to synthesize other bimetallic CPs with a layered structure and their derivatives.2.Microwave-assisted synthesis of porphyrin-based Ce-MOFs and its derivativesMeso-tetra(4-carboxyphenyl)porphyrin has a unique cyclic chemical structure.The-COOH attached to the benzene ring can provide a chelating site and can effectively bond with metal ions.Because the microwave-assisted synthesis method has the advantages of high energy and short reaction time,it greatly increases the nucleation rate of MOFs particles and shortens the synthesis time.In this work,we used the microwave method to assist in the synthesis of porphyrin-based Ce-MOFs,and explored the influence of temperature,heating time,metal ion/ligand molar ratio,and auxiliary ligands on its morphology.Due to the difference in the coordination of Cu,Ce and organic ligands,it is difficult to achieve wide-range control of the two components,only a small amount of Cu doping is allowed to obtain bimetal Ce-Cu MOFs.The results of CO catalysis showed that even a small amount of doped Cu significantly improved the catalytic activity of Ce-Cu-MOFs-derived CeO₂-Cu O catalyst.3.Ce-MOFs involed in the interfacial reaction to prepare CeO₂@Fe₂O₃As mentioned above,how to avoid the homogeneous nucleation of the second-phase metal oxide is the key to obtain MOFs-derived bimetallic oxide.In this work,we selected the Ce(?)-MOFs containing reductive Ce(?)ions to undergo interfacial oxidation-reduction reactions with Na₂Fe O₄,a strong oxidant,to prepare CeO₂-Fe₂O₃catalysts with different Ce/Fe ratios.In the process,the sacrificial template Ce(III)-MOFs reacts with Na₂Fe O₄solution,and Fe(VI)ions are reduced and hydrolyzed on the surface of the template,followed by a in-situ nucleation of Fe(OH)₃.By this methos,the interfacial reaction largely inhibits the homogeous nucleation of the shell material.And through characterization methods such as BET and H₂-TPR,it suggested that the interaction between CeO₂and Fe₂O₃is an important reason for improving the catalytic activity of the catalyst in the photodegradation of methylene blue.At the same time,the interfacial reaction enriches the research system of Ce-MOFs-derived composite catalysts and provides a reference for the synthesis of bimetallic oxide catalysts.