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The Investigation Of CuO-ceO2Oxides Doped With Transition Metals On Their Structure And Catalytic Performance For Selective Oxdation Of CO In H2-rich Streams

Posted on:2013-11-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:J LiFull Text:PDF
GTID:1221330395954439Subject:Physical chemistry
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Hydrogen, a clean renewable energy, meets almost all the energy needs. The most important aspect of hydrogen utilization is that hydrogen converts into electricity, which is a typical utilization in polymer electrolyte membrane cells (PEMFCs). H2-rich streams produced from the steam reforming or autothermal reforming processes is primary fuel source of PEMFCs, and CO purification of the H2-rich streams is of vital importance. Owing to their excellent catalytic performance and low cost CuO-CeO2catalysts become the hot field in recent years. To further improve the catalytic performance of CuO-CeO2catalysts for selective oxidation of CO in H2-rich streams as well as the resistance against CO2and H2O, the introduction of metals into CuO-CeO2formed multi-component oxides, such as alkaline earth metals, rear earth metals and transition metals doping, has earned much attention. As reported in literature, such as by doping a small amount of dopant can improve the interaction between copper and ceria, redox properties and catalytic performance for selective oxidation of CO.In the present dissertation, we use N2adsorption/desorption, X-ray powder diffraction (XRD), the scanning electron microscope (SEM), transmission electron microscope/high resolution transmission electron microscope (TEM/HR-TEM), temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), UV-Raman spectra (UV-Raman), in situ DRIFTs, temperature-programmed desorption (CO-TPD), CO adsorption and catalytic activity test techniques to study systematically the effect of different transition metals (Mn、Fe、Ni、Ti、Cr or Co) doping, Mn loading, Cu/Mn loading and calcination temperature as well as synthesis method of CuO-CeO2catalysts with Mn doping on the structural property, redox property, dispersion and morphology of the active species as well as catalytic performance for CO selective oxidation in H2-rich streams. Some specific conclusions are drawn from this work as follows:1. The effect of different transition metals (Mn、Fe、Ni、Ti、Cr or Co) doping on the structural property, redox property, dispersion and morphology of the active species as well as catalytic performance of CuO-CeO2catalysts for CO selective oxidation in H2-rich streams was investigated. The results show that the catalytic activity for selective oxidation of CO in H2-rich streams follows the sequence of CuC-Mn> CuC-Fe> CuC-Ti> CuC-Ni> CuC> CuC-Co> CuC-Cr. The introduction of Mn and Fe significantly enhance the interaction between copper and ceria, improve the copper species disperse, cause more irons to incorporate into the ceria lattice, favor the reduction of Ce4+→Ce3+and the formation of oxygen vacancies. However, the introduction of Ni and Co inhibit copper species disperse, and some introduced cobalt ions substitute copper ions in ceria lattice, resulting in the dissociation of copper ions from the lattice and the consequent aggregation on the ceria surface. The introduction of Cr greatly weakens the interaction between copper and ceria, decreases the reducibility of copper species and inhibits the formation of Cu+, and thus decrease the ability of CO adsorption and oxidation.2. The effect of Mn, Cu loading and calcination temperature on the CuO-CeO2catalysts with Mn doping structural property, redox property, dispersion and morphology of the active species as well as catalytic performance was investigated. The results demonstrate that CuC-Mn catalyst with5%of Cu and Mn (Mn:Cu=1:5) calcined at500℃shows the best low-temperature activity of CO oxidation with a40℃wide window of CO complete removing as well as a good resistance against CO2and H2O. The appropriate amount of Mn doping and calcination temperature enhance the interaction between active components and ceria, improve the copper and manganese species disperse and reduction.3. The effect of synthesis method (hydrothermal, co-precipitation, impregnation or sol-gel methods) on the structural property, redox property, dispersion and morphology of the active species as well as catalytic performance of CuC-Mn catalysts for CO selective oxidation in H2-rich streams was investigated. The results show that CuMC-HY catalyst has the best low-temperature activity of CO oxidation and the widest window of CO complete removing, and the sequence of catalytic activity is as follows:CuMC-HY> CuMC-SG> CuMC-IM> CuMC-CP. Catalysts prepared by hydrothermal and sol-gel methods exhibit smaller crystallite size, bigger specific surface area, narrower distribution of mesopores, good disperse of copper and manganese species, more irons incorporating into the ceria lattice to form Cu-Ce-Mn-O solid solution, and thus improve the interaction between active components and ceria. For CuMC-HY catalyst, more and stable Cu+species are formed, and manganese species mainly as Mn4+oxidation state are also favorable to the reduction of Cu2+→Cu+, and thus significantly enhance the redox properties. Catalyst prepared by an impregnation method shows some aggregation of copper species on the surface of ceria, and thus inhibits the dispersion of copper species. Catalyst prepared by a co-precipitation method exhibits a strong hydroxylation degree for the surface under the react condition, forms a large amount of formate species, and thus inhibits the interaction between copper and ceria as well as decreases the low-temperature activity of CO oxidation.
Keywords/Search Tags:CuO-CeO2catalyst, transition metal, interaction, CO selective oxidation
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