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Study on Preparation and Performances of CeO2-ZrO2-Al2O3Composed Oxide by Supercritical Antisolvent Process

Author: HuangPan
Tutor: JiangHaoXi
School: Tianjin University
Course: Chemical processes
Keywords: Supercritical antisolvent process (SAS) CeO2-ZrO2-Al2O3 Oxygen storage capacity (OSC) CO oxidation
CLC: X734.2
Type: Master's thesis
Year: 2012
Downloads: 47
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Abstract


Carbon monoxide （CO）, Hydrocarbon （CH） and nitrogen oxide （NOx） are themain components of automotive exhaust, and their harm to the human health and theenvironment is a growing problem with the increasing of the total vehicle ownershipin our country. Ceria-zirconia composed oxides have a bright future in the applicationto control the emission. However, higher requirements for the oxygen storage capacity（OSC） and capacity of resistance to sintering are brought forward with the increasingrestrictions for the standards of the automotive emission. In recent years,CeO2-ZrO2-Al2O3composed oxides have attracted tremendous attention, because theyare hopeful to maintain good OSC of ceria-zirconia oxygen storage materials andhigher capacity of resistance to sintering of Al2O3simultaneously. In this work,CeO2-ZrO2-Al2O3composed oxides were prepared by supercritical antisolventprocess （SAS） and their OSC was studied. The structure-activity relationships werealso analyzed with the results of related physico-chemical characterizations. What’smore, the influence of CeO2-ZrO2-Al2O3supports prepared by SAS process on thestructure and properties of Pd-supported catalysts was also studied.First of all, CeO2-ZrO2-Al2O3solid solutions were successfully synthesized bySAS process. The highest OSC value （122.0mmol-O2/molCeO2） which increased41.77%compared with CeO2-ZrO2was obtained when the concentration ofC9H21AlO3, Ce（acac）3and Zr（acac）4in the mixed soliution were0.2wt%,0.25wt%and0.25wt%, respectively. The highest concentration of oxygen vacancies and thelattice defects were reached at this preparation condition. In addition, the best OSCproperty was achieved when the calcination temperature was at600℃. This could beascribed to the migration of Al3+between the surface and the bulk, which mightenhance the interaction between Al2O3and CeO2-ZrO2in the bulk. Compared withCeO2-ZrO2catalyst, doping Al2O3could improve the OSC property, no matter whatthe calcination temperature was.Since CeO2-ZrO2-Al2O3composed oxides could strengthen the mutual effectbetween Al2O3and CeO2-ZrO2, induce the oxygen vacancies and lattice defectsincreased, the OSC property and the capacity of resistance to the sintering wereimproved. In addition, the interaction between active metal Pd and CeO2-ZrO2-Al2O3 support could be strengthed when CeO2-ZrO2-Al2O3was prepared through SASprocess, which could result in the lower reduction temperature of PdO appeared at125℃and the higher hydrogen consumption amount of448.3μmol/g. The SASprocess showed the advantage to improve the catalytic activity of Pd/CeO2-ZrO2-Al2O3catalyst. At low space velocity, the CO coversion was about100%at250℃, and the advantage of catalytic activity became more obvious at high spacevelocity. This fact could be attributed to the synergistic effect of the strong interactionbetween Al2O3and CeO2-ZrO2in support, as well as the strong interaction betweenactive metal Pd and CeO2-ZrO2-Al2O3support prepared by SAS process.

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CLC: > Environmental science, safety science > Processing and comprehensive utilization of waste > Transportation industry,waste disposal and comprehensive utilization > Highway > Car
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