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Study on the Ce-based Mesoporous Low-temperature Oxidation Catalysts and Ba-based NSR Catalysts

Author: LuoJinYong
Tutor: MengMing
School: Tianjin University
Course: Industrial Catalysis
Keywords: Ceria Oxidation of carbon monoxide Oxidation of propane Synergies Mesoporous structure Nitrogen oxide storage Sulfur removal
CLC: O643.36
Type: PhD thesis
Year: 2009
Downloads: 285
Quote: 1
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Abstract


Catalytic elimination of automobile exhaust pollution, one of the most effective way to improve air quality. Traditional three-way catalyst can not effectively eliminate cold start-up phase emissions of carbon monoxide and hydrocarbons, as well as lean-burn engine emissions of nitrogen oxides, therefore, the development of high-performance low-cost low-temperature oxidation catalyst and a good sulfur resistance of nitrogen oxides storage and reduction catalyst is important. Select a cerium-based composite oxide catalyst to promote a small amount of noble metal as the research object, the H 8 of the catalyst preparation process, the interaction between the components, as well as CO and C 3 catalytic oxidation mechanism of the system;, lean-burn nitrogen oxide storage and reduction catalyst Pt / BA / Al 2 O 3 in-depth study, with a focus on additives Fe added and the preparation method of catalyst microstructure, and to be associated with the storage of the catalyst and sulfur resistance. First, we take advantage of the surfactant-assisted synthesis method the series Co 3 O 4 -CeO 2 composite oxide. BET and pore size distribution test results show that the catalyst prepared by this method has a higher specific surface area and uniform mesopores. The study found that the structure of the catalyst, the catalyst with the package structure, only a small amount of Co ions are exposed to the surface and CEO the 2 interaction. This structure ensures Co 3 O 4 -CeO 2 having the most intense interaction in three-dimensional directions, so that the catalyst exhibit a unique redox properties. The activity test results found that the catalysts exhibit excellent oxidation performance. Structure and mechanism of the results showed that: CO and propane oxidation required the active site of CO oxidation occurs mainly in Co 3 O 4 -CeO 2 interface, and propane oxidation occurs mainly in with surface Co 3 O 4 microcrystalline adjacent lattice oxygen. , After adding a small amount of Pd in ??the catalyst sample to the CO oxidation activity increased sharply increased, significant catalytic synergies exist between i.e. Pd-Co 3 O 4 , but the propane oxidation activity has no effect on the different catalytic mechanism and rate-controlling step determines the presence or absence of the catalytic synergies, pursuant to which we proposed for the oxidation of CO from the molecular level plus before and after Pd distinct kinetic reaction path. To further simplify the preparation steps and ensure that the catalyst has a larger surface area, surfactant-assisted synthesis method has been improved, one-step synthesis method. For the discovery of the universal law of the reaction and to explore new catalytic system, the precious metals and transition metal oxides modulation. The results showed that only a trace amount of Pd catalyst prepared by the method exposed between these Pd species with a transition metal oxide on the surface, but there is a synergistic effect on the CO oxidation. Situ DRIFTS results show that the nature of the synergistic effect of the interaction between the two can generate active oxygen species, these oxygen species can react rapidly with CO generation reaction intermediate product - bidentate carbonate species (1587 and 1285 cm-1). The synergies size vary depending on the degree of strength of the of Pd metal oxide MOx role. FeOx and MnOx both metal oxide CeO 2 can form a solid solution, to promote this interaction, the CO oxidation ignition temperature less added Pd catalyst was reduced by 70 oC and more than 100 oC. Especially Pd-MnO x-CeO 2 catalyst at room temperature CO conversion can be achieved by 80%. But for propane oxidation, the rate-controlling step is the activation of the CH bond cleavage rather than oxygen. CH bond cleavage Difficult depends largely on the d electron structure of 3d transition metal oxide. As the d electrons increases, 3d transition metal oxide oxidation of propane showed bimodal behavior. The paper also studied the addition of additives Fe on Pt / Ba / Al 2 O 3 catalyst structure, NOx storage and desulfurization performance, results show that Fe Add can be suppressed the BaSO 4 particles grow, but save for NOx and sulfur removal is disadvantageous. EXAFS, in situ the DRIFTS and loop TPR Characterization: The results showed that the interaction between the Pt-Ba of the NOx storage and the sulfur removal is very important. PT-BA Room interactions not only promote the storage of the key steps-NOx overflow also helps BaSO 4 selectively reduced to H2S, to promote the removal of sulfur and the regeneration of the catalyst. In Pt / Ba / Al 2 O 3 Fe, experience redox cycling, PT-Fe between the formation of the alloy, making the active site of Pt Fe and its oxides coverage, inhibition of the interaction between the Pt-Ba, resulting in a decreased capacity of the storage capacity and anti-sulfur. Finally, the use of block copolymer P123 as a template for synthesis of mesoporous Pt / the BaCO 3 -Al to 2 the O 3 NOx storage reduction catalyst, compared with the catalyst prepared by conventional impregnation method, a systematic study of the structure and properties of the catalyst. Structural characterization: mesoporous Pt / BaCO 3 -Al the 2 O 3 has a high specific surface area, uniform pore size and higher thermal stability. The the Ba species three-dimensional highly fragmented, with Al 2 O 3 strong role, all the the Baco 3 expressed in the form of low-temperature barium carbonate exists. Compared with the conventional impregnation sample mesoporous samples as NSR catalyst has obvious advantages, such as higher NOx storage capacity, the lower the sulfur adsorption capacity, and strong desulfurization capacity. Adsorption of NOx and SOx generated by the bulk species.

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