Several perovskites of the type La1-xAxCo0.5Cu0.5O3 (A = K, Sr, Ba; x = 0, 0.25, 0.5) and a Sr-doped understoichiometric one,havebeen preparedbycitrate methodaiming atapplication asnoble metals freecatalysts for automotive application. The catalysts have been characterized by BET, X-ray diffraction (XRD), Temperature Programmed Reduction (TPR), X-Ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM)andtheeffectofA-dopinghasbeeninvestigated.Thecatalyticactivitywasstudiedinmodelreactions(CO oxidation, CO assisted NO reduction), and in a complex three way catalysts (TWC) mixture approaching automotive exhaust composition at both stoichiometric and O2-limiting conditions and the obtained results are discussed inrelationwithcharacterization results.A-dopinginducestheformationofhighlydispersedcubicCuO particles, as observed in the understoichiometric samples. Doping also influences the surface segregation. La segregation is observed in the undoped LaCo0.5Cu0.5O3 sample whereas K is surface segregated in La0.75K0.25Co0.5Cu0.5O3; Co segregates in the Ba-doped perovskite and Sr in the understoichiometric La0.35Sr0.35Co0.5Cu0.5O3. The reducibility (TPR) is altered by A-doping. The reactivity results suggest that in simple CO + O2 and CO + NO mixturesthe activation temperature is increased byany doping, but at400 °C the conversion in the CO assisted NO reduction is not significantly different with respect to the one obtained in the undoped catalyst. Activity with a more complex mixture, simulating actual engine exhaust, reveals the interesting activity of the Sr-doped catalysts, that outperform LaCo0.5Cu0.5O3 at both stoichiometric and O2-lean conditions. NO reduction can be achieved at lean O2 conditions, where it is quantitative from 400 °C. The possibility to reach similar or better activity by replacing the use of La, which is a Rare Earth Element, by using Sr is particularly interesting. Stability at high temperatures and at fast fluctuations of O2 in inlet stream for 50% Sr-doped catalyst confirms these results.
On A-doping strategy for tuning the TWC catalytic performance of perovskite based catalysts
GARBUJO, ALBERTO;Pacella, M.;Natile, M. M.;FABRO, JESSICA;Canu, P.;Glisenti, A.
2017
Abstract
Several perovskites of the type La1-xAxCo0.5Cu0.5O3 (A = K, Sr, Ba; x = 0, 0.25, 0.5) and a Sr-doped understoichiometric one,havebeen preparedbycitrate methodaiming atapplication asnoble metals freecatalysts for automotive application. The catalysts have been characterized by BET, X-ray diffraction (XRD), Temperature Programmed Reduction (TPR), X-Ray Photoelectron Spectroscopy (XPS), and Scanning Electron Microscopy (SEM)andtheeffectofA-dopinghasbeeninvestigated.Thecatalyticactivitywasstudiedinmodelreactions(CO oxidation, CO assisted NO reduction), and in a complex three way catalysts (TWC) mixture approaching automotive exhaust composition at both stoichiometric and O2-limiting conditions and the obtained results are discussed inrelationwithcharacterization results.A-dopinginducestheformationofhighlydispersedcubicCuO particles, as observed in the understoichiometric samples. Doping also influences the surface segregation. La segregation is observed in the undoped LaCo0.5Cu0.5O3 sample whereas K is surface segregated in La0.75K0.25Co0.5Cu0.5O3; Co segregates in the Ba-doped perovskite and Sr in the understoichiometric La0.35Sr0.35Co0.5Cu0.5O3. The reducibility (TPR) is altered by A-doping. The reactivity results suggest that in simple CO + O2 and CO + NO mixturesthe activation temperature is increased byany doping, but at400 °C the conversion in the CO assisted NO reduction is not significantly different with respect to the one obtained in the undoped catalyst. Activity with a more complex mixture, simulating actual engine exhaust, reveals the interesting activity of the Sr-doped catalysts, that outperform LaCo0.5Cu0.5O3 at both stoichiometric and O2-lean conditions. NO reduction can be achieved at lean O2 conditions, where it is quantitative from 400 °C. The possibility to reach similar or better activity by replacing the use of La, which is a Rare Earth Element, by using Sr is particularly interesting. Stability at high temperatures and at fast fluctuations of O2 in inlet stream for 50% Sr-doped catalyst confirms these results.
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