Abstract
In this study, Pd/LTA and Pd/SSZ-13 were prepared and then hydrothermally aged at the temperature of 750, 800, 850, and 900 °C. Multiple Pd species, including isolated Pd ions (Pd2+ and [Pd(OH)]+) and 1∼2 nm PdOx nanoparticles, were presented in two fresh samples. The Pd/LTA sample showed remarkable hydrothermal stability, but the Pd/SSZ-13 sample experienced severe damage after aging at 900 °C. The destruction of the aged Pd/SSZ-13 sample led to the migration and sintering of PdOx nanoparticles, which formed bulk PdOx particles on the surface of the zeolite crystallite. A large number of PdOx nanoparticles were retained after aging of the Pd/LTA sample. Pd/LTA contained a higher concentration of Pd2+ sites, while Pd/SSZ-13 had more [Pd(OH)]+ sites. It is found that the improvement of NO adsorption ability with CO addition onto Pd2+ was more significant than onto [Pd(OH)]+.
Highlights
IntroductionNitrogen oxides (NOx) in the exhausts from lean-burn engines (i.e., gasoline and diesel), entail significant challenges for the aftertreatment society [1]
Nitrogen oxides (NOx) in the exhausts from lean-burn engines, entail significant challenges for the aftertreatment society [1]
The zeolite structure of the Pd/LTA sample was well maintained after harsh aging up to 900 °C, the structure of the Pd/SSZ-13 sample experienced severe damage due to dealumination
Summary
Nitrogen oxides (NOx) in the exhausts from lean-burn engines (i.e., gasoline and diesel), entail significant challenges for the aftertreatment society [1]. One of the main reasons for this is that the ammonia is supplied through a urea solution and urea cannot be dosed below 200 °C, since at low temperature deposits form, such as biuret and cyanuric acid [8]. One possible approach is to employ a material that can adsorb NOx (mainly in the form of NO) at a low temperature (below urea dosing temperature) and to desorb it at a high temperature, e.g., 200−400 °C. This material is called a passive NOx adsorber (PNA) catalyst [9,10]. Using PNA and SCR components simultaneously in the aftertreatment system, where
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