Interfacial Reaction Involved Synthesis Of MOFs-Derived Bimetal Oxides And Their Formation Mechanism And Catalytic Performance Study

The synergistic effect between different components in bimetal oxides often makes their catalytic performance superior to that of single-component metal oxides,and as we know,the catalytic performance is closely related to the morphological structure and components of the bimetallic oxide and other factors.Therefore,when the above factors are regulated reasonably,it is expected to achieve a class of catalysts with high catalytic activity.According to the research results,the pyrolysis of MOFs to prepare bimetal oxide catalysts is a simple and effective strategy,because MOFs have a rich morphological structure,adjustable composition,rich pore structure and high specific surface area,which provide convenient conditions for this strategy.The bimetal oxides obtained through the pyrolysis of MOFs can usually inherit the MOFs features including the morphology of original MOFs,high specific surface area and uniform distribution of components.Unfortunately,some metal ions are not easily to form bimetallic MOFs due to their different coordination behaviors.As a result,some bimetal oxides can not obtained by the pyrolysis of bimetallic MOFs Therefore,we designed different kinds of interfacial reactions involving single metal MOFs?or MOFs derivatives?to prepare bimetallic oxides,which not only maintains the rich pore structure and high surface area after thermal decomposition of MOFs,but also leads to the second metal oxide that has a close contact with metal oxides derived from the MOFs.Obviously,the close contact between individual component enriches the contact interface and facilitates the interaction between the two species in the catalytic reaction.The paper focuses on controlled synthesis of bimetal oxide catalysts with porous structure,intimate components contact and uniform components distribution by means of different kinds of MOFs involved interfacial reactions.In addition,the preparation,structure characterization,formation mechanism,and catalytic performance of the catalysts are all investigated.1.MOFs-derived carbon involved interfacial reaction for the synthesis of CeO₂-MnO₂catalystsCeO₂-MnO₂ catalysts with different Ce/Mn ratios were successfully prepared by interfacial reaction between Ce-MOFs derived carbon and KMnO4 aqueous solution.Specifically,CeO2/C composites were obtained after pyrolysis of rod-shaped Ce-MOFs in an inert atmosphere.Then,the interfacial reaction between MOFs-derived carbon and KMnO₄generates MnO₂ in situ of the carbon,resulting in the MnO₂ replaces carbon in close contacted with CeO2 after thermal decomposition of Ce-MOFs,which is conducive to enhancing the interaction between two components.Experimental results indicate that MOFs-derived carbon can restrain the growth of CeO₂ crystalline grains at high calcination temperture.According to a series of characterizations such as XPS,Raman,and H₂-TPR,CeO₂-MnO₂-13.6 mol%components have the strongest interaction and exhibit the highest catalytic activities for CO oxidation.2.Organic ligands in MOFs involved interfacial reactions for the synthesis of porous/hollow Co₃O₄-MnO_x catalystsMOFs with hollow structures are supposed to expose more active sites and to provide channels for rapid diffusion of reaction substrates and products.So far,most of the MOFs with hollow structures are obtained through hard template-engaged method,which generally requires template surface modification and post-template removal process.In our work,we designed organic ligands-involved interfacial reaction.In other words,the hollow structured MOFs can be achieved by the exchange of organic ligands.Specifically,because the coordination ability of 2,5-dihydroxyterephthalic acid with metal ions is stronger than that of2-methylimidazole,a ligand exchange reaction occurs when Co/Mn-ZIFs acts as a template to react with 2,5-dihydroxyterephthalic acid within ethanol solution.At the beginning of the reaction,the Co/Mn-MOF-74 shell was formed on the surface of the Co/Mn-ZIFs particles,the internal Co/Mn ions continued to diffuse to the outside to react with2,5-dihydroxyterephthalic acid as the reaction time increases,leading to the formation of a hollow structure due to the Kirkendall diffusion mechanism.Obviously,this method avoids the complicated steps of removing the template and synthesizes the hollow structured material within one step,which enriches the preparation method of the bimetallic MOFs with hollow structure.Even if the Co₃O₄-MnO_x catalyst is obtained by calcination,the hollow structure maintains.The catalytic results show that Co/Mn-MOF-74 and Co₃O₄-MnO_x exhibit their bimetallic synergistic effect in both liquid-phase hydrogenation and CO oxidation.3.Cations in MOFs involved interfacial reactions for the synthesis of hollow CeO2-Co3O4catalystsCo₃O₄ is an excellent metal oxide catalyst which exhibits high intrinsic activities in CO oxidation reaction.Due to CeO2 has a good ability to release/storage oxygen,so the CeO₂-Co₃O₄ is expected to improve the active oxygen transport capacity,and there is a synergistic effect between Co₃O₄ and CeO₂ to promote the improvement of catalytic activity.When the two components of Co₃O₄ and CeO₂ can be in close contact,it can effectively suppress the sintering of the particles of the two species,improve the utilization of the active species,and fully exhibit all the advantages of components in catalysts.CeO2-Co3O4 catalysts with a hollow structure are supposed to increase the specific surface area,expose more active sites and accelerate the diffusion of substrate molecules in reactions.In this context,ZIF-67 as a sacrificial template,and H⁺released from the hydrolysis of Ce³⁺as an etchant were used to synthesize CeO2-Co3O4 catalysts through a solid-liquid interfacial reaction.The Co/Ce molar ratio in the as-prepared catalysts can be adjusted by the concentration of Ce³⁺,and the composition effect is also studied to explore the structure-activity relationship in details.