Dissertation > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst

Fundamental Study on Ceria-zirconia Solid Solution Supporting Copper Oxide Nanocatalyst for NO Reduction

Author LiuLianJun
Tutor DongLin
School Nanjing University
Course Chemistry
Keywords Ceria-zirconia solid solution Copper oxide Dispersion Embed Interaction NO reduction
CLC O643.36
Type PhD thesis
Year 2010
Downloads 256
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Ceria-zirconia solid solution with good oxygen release oxygen storage performance and redox, as an important component of the three-way catalyst used in motor vehicle exhaust gas purification. Research dispersed state copper species in the coordination of its surface structure and surface properties, the design and efficient elimination of NO catalyst is important. How to improve the low-temperature activity and selectivity of NO reduction, as well as recognize the reduction of NO adsorption reaction mechanism worthy of further study. Therefore, the combination of thermogravimetric differential thermal analysis, X-ray diffraction, Raman spectroscopy, UV-visible absorption spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, hydrogen temperature-programmed reduction, in situ infrared and NO CO model reaction and other means of copper-cerium-based catalysts to characterize the main purpose is to study (1) of the carrier (γ-Al2O3, t-ZrO2, CeO2, Ce0.67Zr0.33O2, defined as CZ) structure of copper-based catalyst activity and adsorption behavior impact; (2) Co and / or the NO molecule with CuO / CZ catalyst interaction, the states before and after the catalytic reaction, and NO CO possible reaction mechanism; (3) COOX, of the MnOx Modified on CuO / CZ catalyst reducing properties, adsorption behavior and activity; (4) CuO/CexZr1-xO2 (x = 0.2,0.5,0.8) structural features of the catalyst in the reaction of NO CO relationship between the catalytic properties; (5) nano ceria-shaped Maung and exposed crystal face of CuO/CeO2 catalyst for catalytic reduction of NO activity. The results show that: (a) dispersing the state copper species can be embedded in the carrier surface vacancies, in cerium oxide (111) plane of a penta-coordinated structure is asymmetrical, in the tetragonal zirconia (111) surface is stretched trigonal bipyramidal structure , while the (110) on the alumina surface is symmetrical octahedral structure. Surface structure similar synergy between the carrier and copper species differences, so CuO/CeO2 catalyst showed strong low temperature reduction and reduction of NO activity. In situ infrared NO adsorption / desorption results show that compared with adsorption in the surface of CuO/γ-Al2O3, CuO/t-ZrO2 NO species adsorbed cerium-rich phase catalyst the surface chelate nitroso, bidentate and monodentate nitrate is very active, it is easy desorption or conversion, and higher than 100 ° C due to the formation of oxygen vacancies NO electronics generate NO and aggregate to form dithionite nitrate. Situ infrared coadsorption results show that the type and activity of the adsorbed NOx species depends on the carrier structure and reaction temperature. Relative to the other samples, is adsorbed on the surface chelate nitroso of CuO/CeO2 bridge and bidentate nitrate is very reactive at low temperatures and CO reaction. (B) For xCuO / CZ system, the dispersed state of copper oxide is the principal active species in the reaction. Exhibit different activity and selectivity of the catalyst at low temperature and high temperature phase, is composed of a dispersion state copper species is reduced due. This also shows that the change due to the active species in the high temperature, the reaction is carried out at low temperature and high temperature will experience a different reaction mechanism. Situ IR The results show that (1) CO is derived from the vector of the activity of oxidized by oxygen, resulting in generating surface carbonates, and the part of the copper oxide in 15 ℃ will be reduced by CO into of Cu; (2) NO and dispersed state CuO The role can be formed of various structures in the form of nitrate and nitrite species, while the crystalline phase of copper oxide does not cause a new NO adsorption species generated; (3) in the mixed reaction atmosphere, NO molecules preferentially catalyst. These adsorbed species exhibit different thermal stability, and the reaction occurs at 250 ° C will CO. (C) For the purposes of the CuO-COOX binary oxide system, a copper oxide and cobalt oxide (load amount is less than 0.5 and 0.32 mmol/100m2 CZ) can be highly dispersed on the carrier surface. Cobalt species can promote copper species and the reduction of the surface oxygen, and it can improve the reaction activity, mainly because there is a strong interaction between the copper and cobalt oxides to thereby form the Cu-O-Co bond, depending on the load of impregnation sequence and drill amount. Meanwhile, due to the dispersion of the interaction between the state of cobalt and cerium-zirconium carrier surface cause the surface oxygen is easily released, active oxygen can be the oxidation of NO molecules aggregate into N03-1 ion. MnOx modified CuO / CZ system, on the one hand, the addition of manganese oxide and copper oxide causes cerium zirconium carrier lattice expansion and lattice stress results induce more oxygen vacancies. The same time surface copper, manganese species and between the cerium-zirconium carrier charge migration occurs, i.e. of Cu2 of Mn2 (?) Cu of Mn3; CE4 of Mn2 (?) Of Ce3 of Mn3; the other hand, the addition of manganese oxide can effectively contribute to the reduction of the catalyst assist copper the species rapidly changing valence and the carrier surface oxygen. The reduction behavior depends on the manganese loading and impregnation sequence. In addition, the introduction of manganese species does not change the NO molecule adsorption structure, they will not create a new species, but can be activated NO adsorbed species, reduce the desorption temperature. Therefore, these factors determine the MnOx modification can significantly improve the activity and selectivity of the reaction. (D) CuO dispersion capacity in CexZr1-xO2 surface by the impact of the surface of the support structure, Rich cerium (pseudo-cubic t ') the phase (quad t) than the zirconium-rich more effectively dispersed and anchor surface copper species. Copper species in the carrier surface and epitaxial growth, by occupying the carrier (111) surface of the vacancy thus embedded in the surface of the lattice, the results with the cerium-rich phase vector generated a stronger synergistic. The the catalyst coordination environment and lattice stress is CuO/CexZr1-xO2 affect one of the synergies of the reasons for the differences between the copper oxide and the carrier. On this basis, put forward the copper species embedded in the ceria-zirconia solid solution body surface possible model structure, that the dispersed state of oxidation of copper rich cerium phase (t \lattice stress with zirconium-rich phase catalyst compared Rare has a greater ability to promote copper species and the reduction of the carrier surface oxygen. situ infrared results show that the synergy between the dispersed state of copper species and pseudo-cubic phase the effect is more likely to promote CO the desorption activation of NO adsorbed species, but for the tetragonal phase catalyst is relatively difficult. therefore the, CuO/Ce0.8Zr0.202 the catalyst than CuO/Ce0.5Zr0.502 CuO/Ce0.2Zr0.8O2 show more high NO reduction activity. (e) CeO2 nano polyhedron and cubes (they were mainly exposed (111) and (100) planes) the Ce02 nanorods (preferentially exposed (110) and (100) planes) can be more effective dispersed and anchoring surface copper oxide species. stronger interaction exists between CuO and CeO2 nanorods dispersed state, resulting in stronger reducing ability, and the higher the NO reduction activity of the catalyst. according to the proposed The surface model that Cu2 ions occupy the vacancies of the cerium oxide and embedded into the surface of the crystal lattice, and the (111), (110) and (100) plane is in a different ligand environment Thus, such different surface structure effect can result in differences in the geometric spatial structure of the dispersed state of the copper oxide species, thus affecting between CuO and CeO2 synergies, CuO/CeO2 nanorod lattice stress, thus five-coordinate structure is unstable; CuO / CeO2 lattice stress is smaller, and thus more stable octahedral structure, the result will inevitably bring about the differences of the surface of the catalytic properties of copper oxide species.

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