Pd/SSZ-13 samples with the same Pd loading (1 wt.%) but different Si/Al ratio (6 and 13) were hydrothermally aged at 800, 850, and 900 ºC, respectively. The Pd/SSZ-13 with a lower Si/Al ratio suffers a more severe deactivation. The Pd/SSZ-13 with a Si/Al ratio of 6 experiences structural damage due to dealumination, while the structure of the sample with a Si/Al ratio of 13 remains intact. The agglomeration of Pd 2+ ions to large PdO particles on the external surface of zeolite causes the deactivation. The Pd cations are mobile during aging. Besides dealumination, the Pd 2+ ions might be hydrolyzed and have a high mobility, which also results in the Pd 2+ ions agglomeration. The severe dealumination causes the deactivation after aging at 900 ºC. However, the Pd mobility might be the primary reason for the decline of NO adsorption capacity of Pd/SSZ-13 after aging at 800 and 850 °C.
- low-temperature NO adsorption
- hyhdrothermal aging
- Pd mobility