Components Interactions And Optimizations Of Barium-ceria Based NO_x Storage Reduction Catalysts

Lean-burn combustion has gained its popularity because of the less emission of green-house gases, CO, and particle materials. NO_x is very challenging for decent control due to the oxygen rich atmosphere. NO_x storage reduction (NSR) technology has become a promising method for efficient NO_x abatement in lean-burn gasoline engines and light-duty diesel engines, demonstrating the merits in good efficiency, no additional reducing agent, and limited cost. The well design of NSR catalysts based on detailed fundamental understanding holds the key to the safe application of the NSR system for cars.The present work is going to investigate the Ba-Ce based interactions and optimizations in NSR catalysts. The major tasks include the design of the dynamic NSR evaluation system, aging protocols, and in-situ characterizations. A novel aging protocol as 12 h 10 % CO₂ 10 % hydrothermal aging has been proposed upon systematic comparisons. The tiny possibility of detrimental BaCeO₃ formation under lean-burn condition has been confirmed, bringing special advantage of CeO₂ supported catalysts over the others. Direct Ba-Ce contact facilitates periodically efficient NO_x trapping and release, and the anionic vacancies and lattice oxygen also benefits the formation of N2 with higher selectivity under rich periods. Alumina is able to provide stable high surface areas and porous structures to disperse the active phases. However, surface acidity of alumina brings deactivation for the barium species in close contact, and BaAl₂O₄ will be able to be formed after aging, suppressing the NSR activity significantly.Among the different ways in introducing barium and ceria, B-C/A sample shows the best activity with the optimal Ce:Al molar ratio as 3:1, where the adequate Ba-Ce contact has been maintained and the porous structure of alumina has been physically utilized. Below the optimal ratio, ceria patches strongly coordinate with alumina lattice, showing little activity for NSR process. When ceria content increases, less active bulk structured ceria particles aggregate on alumina surfaces, exposing more chances for detrimental Ba-Al contact.