Ce-MOFs As A Precursor For Synthesis Of Derivative Catalysts For CO Oxidation

In recent years,socio-economic development has been rapid,but it has also brought a series of environmental problems.Among them,air pollution is one of the most difficult problems to solve in all environmental issues.As a typical atmospheric pollutant,CO gas has a wide range of sources,and it seriously harms human life,health and production.Among the many methods used for CO removal,the catalytic oxidation method is often used as a research focus because of its high efficiency,low price,and less secondary pollution.Therefore,a new type of CO catalyst with high activity and high stability has been developed.It is of great significance to promote the practical application of fuel cells for the removal of CO in air and the problem of CO poisoning in Pt electrodes of fuel cells.Recently,metal-organic framework（MOFs）materials have a variety of structures,large specific surface area,high porosity,adjustable pore structure,and rich metal defect sites,and can form periodic networks with organic ligands through self-assembly.The structure of a new type of porous functional materials and a series of advantages,often used to synthesize various metal oxides.Studies have shown that with the use of MOFs as precursors,mesoporous carbons with special pore structures and metal oxide nanomaterials with specific morphology and size can be prepared.Combined with domestic and international reports,it has been found that CeO₂,a rare earth metal antimony metal oxide,has excellent oxygen storage performance and redox ability.At present,there is no relevant research on preparation of antimony oxide for CO oxidation using MOFs as precursors.Therefore,in this paper,a Ce-based MOFs material（Ce-BTC）was prepared as a precursor of CeO₂ catalyst.By controlling the crystallization conditions,calcination temperature and other factors,the catalysts of Ce-BTC and CeO₂ were studied systematically in an oxygen-rich atmosphere.Performance of CO oxidation;In addition,we also incorporated Cu species into Ce-BTC,and studied the role of CuCe composite oxide catalysts in CO oxidation in an oxygen-enriched and hydrogen-rich atmosphere.Through the above series of research work,we have achieved the following results:1.A straw-shaped Ce-BTC catalyst with uniform morphology was prepared by controlling the temperature and time of hydrothermal reaction,and a series of Ce-BTC derivatives were prepared through direct calcination of Ce-BTC precursor under different temperature or time.The physicochemical properties of the catalyst were analyzed by XRD,BET,FT-IR,SEM,H₂-TPR,XPS,UR-Vis,PL and Raman.The results show that the catalytic activity of CO of Ce-BTC derivatives increases first and then decreases with the increase of calcination temperature.When the calcination temperature is 250 ℃,it has the best catalytic activity and can reach 98%conversion rate of CO at a reaction temperature of 320 ℃.It was found that when the pretreatment temperature reached 250 ℃,part of Ce³⁺in Ce-BTC material began to transform into Ce⁴⁺,and the crystal structure of MOF still existed.However,the BET analysis showed that the specific surface area of the Ce-BTC material after calcination at 250 ℃ increased sharply to 648 m² g^-1,and its large specific surface area provided more exposed sites for the remaining Ce³⁺,which showed higher CO performance.When the temperature reaches 300 ℃,the organic skeleton in the Ce-BTC material begins to collapse,the specific surface area decreases,and a large amount of Ce³⁺is converted to Ce⁴⁺,and the CO oxidation performance of the Ce-BTC material decreases.In addition,the crystal structure of Ce-BTC₂₅₀ derivatives has been completely converted to CeO₂after catalytic reaction,which has good catalytic activity,long-term stability and water resistance.Moreover,the catalyst after the reaction still has a large surface area and the strawsheave-like morphology.2.A series of CeO₂ derivatives were successfully achieved through direct decomposition of Ce-BTC under different temperature（400-700℃）in air.Several analytical tools such as Scanning electron microscopy（SEM）,X-ray diffraction（XRD）,Thermogravimetric（TG）,N₂ adsorption-desorption,Temperature programmed reduction（TPR）,Raman,X-ray photoelectron spectroscopic（XPS）and Photoluminescence（PL）have been used to characterize CeO₂.The Ce-BTC calcined at500oC（CeO₂-500）maintains the morphology of its template“Ce-BTC”and forms a special cauliflower-like structure.XRD patterns showed that the catalyst had a perfect CeO2 crystal structure and had a smaller particle size.The prepared CeO₂ cauliflowers exhibit excellent catalytic activities,long-term stability,and cycling stability for CO oxidation.The improved catalytic activities could be attributed to porous nanorods of CeO2 cauliflowers,which provide more active sites and oxygen vacancy for CO oxidation.3.A series of Ce（Cu）-BTC materials were prepared by modulation synthesis and Cu loading.After calcination at 500 ℃,CO oxidation was performed and CO selective oxidation performance under hydrogen-rich conditions was studied.XRD,BET,FT-IR,SEM,H₂-TPR,XPS,UR-Vis,PL,Raman,etc.were characterized.The results show that the preparation method of precursor Ce（Cu）-BTC has a significant effect on the structure and catalytic activity of the catalyst.The CuO/CeO₂ composite catalyst prepared by calcining the Ce（Cu）-BTC precursor synthesized at 500 ℃ with the use of ethanol as the solvent and in-situ addition method at a Cu content of 5%is suitable because the CuO is good on The CeO₂ carrier.Dispersion and high concentrations of Ce³⁺and Cu⁺therefore exhibited the best catalytic activity(T₉₈=100 ℃).