Study On Preparation And Performances Of CeO₂-ZrO₂-Al₂O₃Composed Oxide By Supercritical Antisolvent Process

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.