Silver and palladium ion-exchanged BEA zeolites (Si/Al = 12.5) and silver ion-exchanged ZSM-5 zeolites (Si/Al = 15) were studied for their ability to adsorb and desorb propylene and NO under simulated diesel exhaust conditions. The adsorption experiment results demonstrated the excellent ability of bare BEA zeolites to adsorb propylene, but only a small amount of NO. The presence of H₂O inhibited the adsorption of both C₃H₆ and NO. Ion-exchanging BEA zeolites with Ag (1.2 and 5.1 wt.% Ag/BEA) attenuated the inhibiting effect of H₂O on C₃H₆ adsorption, while NO storage remained inhibited. Adsorption experiments indicated that C₃H₆ and NO competed with each other for Pd sites with C₃H₆ showing stronger adsorption compared to NO, whereas Ag sites preferentially adsorbed C₃H₆. DRIFTS data indicated the formation of nitrate, formate and acetate species on Ag and Pd, while C₃H₆ and NO adsorption was also observed on the zeolite hydroxyl groups in the absence of H₂O. However, the C₃H₆ and NO adsorption on the zeolite hydroxyl groups was significantly inhibited in the presence of H₂O. Additionally, nitrosyl, acrolein and carbonate species were formed over 1.0 wt.% Pd/BEA. The effluent analysis during the temperature-programmed desorption in the DRIFTS reactor revealed that adsorbed C₃H₆ and NO reacted during the release to form oxidation reaction byproducts. The 1.0 wt.% Pd/BEA zeolite showed the greatest oxidation ability during desorption with the majority of stored C₃H₆ converted to CO₂.