Microwave Synthesis Of MOFs-derived Cu-Ce Catalysts And Their Application In CO-PROX

Metal-organic frameworks（MOFs）derives effectively inherit the property of MOFs,including the high dispersion of metals or metal clusters,porous structure and large specific surface and so on,which are facilitating to construct the catalytic activity species from MOFs precursor.Especially,its design and derivative process can be precisely optimized according to the demands of special catalytic active sites due to the tunable coordination between metal atoms and organic ligands in the self-assembly MOFs.Herein,the advantages and regulation effects of microwave were explored in the synthesis of well performance Cu-Ce catalysts,which were prepared from MOFs precursor for CO preferential oxidation（CO-PROX）in H₂-rich steam.In this paper,microwave synthesized MOFs derived Cu-Ce catalysts are designed and studied in the following five sections.Part I:By constructing hollow spherical supported MOFs precursors,the active copper species are allowed to disperse to a larger extent on the outer surface of hollow ceria spheres supported in bulk microwave synthesis.Derived Cu-Ce catalyst solves the problem of coating of active sites,exposing the active Cu-O-Ce interface sufficiently.Furthermore,layer by layer（LBL）synthetic method of MOFs realizes an ordered and stable growth of Cu-MOF on the hollow Ce O₂ shell.While avoiding extra nuclear growth effectively,the loading amount of Cu species can be precisely controlled by adjusting the number of layers,resulting in the optimal precursor structure composition.The optimum conditions for hollow sphere catalyst synthesis are as follows:the Cu-MOF loading is 10 layers,and the pyrolysis temperature is700°C.Part II:Efficient CO-PROX catalytic activity formation conditions are examined by comparing the active Cu-O-Ce interfacial loading of catalysts that four different morphologies as well as different loading regimes of MOFs.The advantages of hollow sphere Ce O₂ support are verified from three aspects:（1）Spherical and rod-shaped Ce O₂ can stabilize the supported MOFs uniformly by comparing four morphologies（rod,sphere,cube and octahedron）due to their（002）low-energy crystal planes.（2）The supported Cu-MOF strategy overcomes the drawbacks of inhomogeneity in the distribution of metal ions inside the microporous of MOFs,which is superior to the general MOFs pore channel metal leaching method.Thus,the inability of active sites can be exposed outside sufficiently.（3）The advantage of precise loading of MOFs solves the agglomeration of active sites brought about by the uncontrollable process of impregnation loading of metal ions.In this paper,the active mechanism of CO-PROX reaction over dominant hollow spherical Cu O/Ce O₂is comprehensively analyzed by in-situ Raman and in-situ diffuse reflectance infrared Fourier transform spectroscopy（in-situ DRIFTs）.Part III:Microwave efficient electromagnetic energy provides a completely new derivative path of MOFs,namely,satisfying the intermolecular coupling effect while endowing MOFs with an efficient and thermally uniform derivative process.Microwave coupled Cu-Ce interactions enable the formation of active site with rich oxygen vacancies to enhance CO-PROX catalytic activity.The highly dispersed precursor of cerium and copper are formed by the bimetallic MOF（Cu Ce-MOF）.Subsequently,the tandem microwave pyrolysis is adopted to expand the molecular design engineering of MOFs precursor:Firstly,the microwave absorption performance of MOFs is improved by carbonization ligand,which constructs a molecular scale heating source,and then microwave pyrolysis Cu Ce/C coupled to obtain an efficient Cu-Ce catalyst.Hence,microwave pyrolysis effectively display extend and inherit the engineering concept of molecular design from MOFs,the Cu-Ce catalyst exhibit a high improvement in CO-PROX catalytic activity by microwave pyrolysis.Thus,the sufficient selective oxidation of CO can be achieved at 75°C.Part IV:Non-thermal effects promote the derivative process of MOFs,such as electric and magnetic.A low-temperature microwave fusion derived MOFs strategy for the fabrication of highly active Cu O/Ce O₂ is proposed by analyzing and rationally designing the introduction of microwave non-thermal effects.Cu-MOF preferentially carbonized to form a differential intermediate species with microwave absorption characteristics at appropriate temperature in N₂ atmosphere,the MOFs precursor is a physical mixture:Cu-MOF&Ce-MOF.The higher microwave absorptive Cu/C species migrate spontaneously towards Ce-MOF with low absorptive characteristics under the assistance of microwave-induced action.Thereby,the fusion of copper and cerium is excited by microwave dipole vibration.Subsequently,the oxidative coupling is finally completed in air.The microwave pyrolysis temperature reduce200°C than that of the traditional pyrolysis,and in-situ techniques reveal that the microwave non-thermal fusion of abundant oxygen vacancies in Cu-Ce catalyst is the critical factor for boosting CO-PROX.Part V:Microwave electromagnetic loss can effectively compensate the thermal action on the active interface derived from MOFs.In this part,a trimetallic Cu Co Ce-MOF is derived to construct Cu-Co-Ce oxidation active interface oriented by magnetic,conduction and relaxation loss,which inhibit the high temperature deactivation due to sintering.Equipped with the tandem microwave pyrolysis,the intermediate Cu Co Ce/C fully exposes electromagnetic characteristic and heterogeneous interfaces.Subsequently,microwave strengthened Cu Co Ce O_x exhibits a broadened CO-PROX activity window with the more than 85%CO conversion at80-210°C.In-situ Raman and in-situ DRIFTs investigations demonstrate that the equilibrium on active interfacial oxygen vacancy via hydrogen is the crucial for the temperature window broadening of CO-PROX.