CO effects on Pd-BEA and Pd-ZSM-5 as model catalysts for passive NOx adsorption
Yuntao Gu, University of Virginia
Cold start emission control is a challenge and among proposed solutions, passive NOx adsorbers are proposed. As potential candidates for passive NOx adsorbers, both Pd-BEA and Pd-ZSM-5 have been reported to have significant low-temperature NOx adsorption capacities, as well as relatively appropriate desorption temperatures. However, their real exhaust compatibility has not been completely evaluated or understood. CO is one of the main components of vehicle emissions and has been shown to impact passive NOx adsorption. Therefore, the NO and CO co-adsorption mechanism on Pd-BEA and Pd-ZSM-5 systems was investigated using in-situ DRIFTS and transient NOx adsorption experiments and temperature programmed desorption/oxidation were used to evaluate the performance of these catalysts under more realistic exhaust conditions. Comparing the NOx storage performance evaluated from a bench-scale reactor and the surface chemistry obtained from DRIFTS leads to a better understanding of the long-term behavior, and provides different insights of CO effects. TPD/TPO results with different aging conditions and pretreatment methods indicate that Pd speciation and the distribution of Pd over different zeolitic systems are essentials to low-temperature NOx storage efficiency and long-term durability.