Study Of The Interactions Of Storage Components-Support Oxides And NOx Storage Stability In Low Temperature Over NOxStorage Reduction Catalyst

NOxstorage and reduction (NSR) is one of the most efficient NOxremovaltechnologies. It was composed of three major components. The complex catalyticconversion processes, and the forms of support oxides and storage components,significantly affect the NSR performance and NOxstorage stability. The design anddevelopment of the high-performance NSR materials is the core of this technology.The electrical conduction path of NSR catalytic reaction, the interactions of storagecomponents-support oxides, the transformation rule of components, materialmicro-chemical structure, and design, preparation and optimization of the overallportfolio is in the field of science and technology research hot spot. Herein, Pt/Al2O3part was blended with storage materials as physical mixtures to form NSR catalysts.The present work investigates the catalytic performances ofPt/Al2O3+Ba/CeO2-ZrO2NSR catalysts. The interests were focused on the effects ofCe–Zr compositions as support oxides to barium species in NOxstorage and releasecycles. Higher Ce content favors rapid NOxup-taking and stable adsorption inadequate amount of small BaCO3particles. The increasing amount of Zr inCexZr1xO2may benefit the formation of porous texture, but it brings the higher riskof BaZrO3formation during the ageing. Additionally, the introduced ZrO2mayincrease oxygen mobility to improve redox activities of the catalysts. Thisimprovement could lower the NH3release in rich period. However, to anotherextreme, a too strong oxidative activity is going to inhibit the NOxreduction due to itsstabilization to intermediate species.The structures, stability and catalytic behaviors of Pt/Al2O3+Ba/CeO2-Al2O3NSR catalysts were investigated. B-C/A shows the best performance due to the highersurface coverage of alumina surface with well-dispersed and uncoordinated ceriapatches, and high coverage of active BaCO3particles on the surface of ceria. Ba-Cechemical interactions are benefitting activation of basic barium species.The low-temperature NOxstorage efficiency of Ce-containing lean NOxtrapcatalysts was investigated using temperature program adsorption. As temperatureincreases from100°C to150°C, the rate of NOxstorage slows down over thecatalysts containing ceria as storage phase, while this phenomenon is less obvious ifceria is used as the support for barium oxides. It was found that the NOxrelease wasmainly from ceria. Thus, nitrite species are formed on ceria during the NOxstorage at low temperatures, and the nitrite species can be activated and transformed to nitratespecies upon further oxidation, accompanied by NO release; on the other hand, NOrelease occurs weakly on barium/ceria as the nitrites are more stable on the more basicBa phase than on the ceria.The Ce/Zr-containing catalysts maintain the cumulative NOxstored after thermalaging. FCZ64, FCZ82and ACZ64show significant improvement in slowing downthe premature NO release. However, an obvious NO release still occurs on ACZ82. Itwas found that nitrites oxidation by lattice oxygen of Ce/Zr was promoted on the freshsamples, resulting in low coverage of nitrite with high stability. On the other hand, alarge amount of nitrite was formed on ACZ82, which could desorb upon increasingtemperature. Segregation of CeO2from the Ce/Zr phase may have occurred onACZ82, resulting in a lower stability of the nitrite species.