Ethylene Trapping of Palladium-Impregnated Zeolites for Cold-Start Emission Control

Zeolite-based trapping materials have drawn a keen interest in hydrocarbon mitigation during cold-start periods at which catalytic converters for vehicles can hardly be activated. However, although C 2 H 4 is one of the major components emitted from auto engines, trapping materials for C 2 H 4 have not been well studied. Here the C 2 H 4 adsorption and desorption properties of palladium-impregnated zeolites with different pore systems (i.e., Pd-beta, Pd-ZSM-5, and Pd-SSZ-13) but similar Si/Al ratios (13-16) and Pd loadings (0.81-0.91 wt.%) have been investigated under both dry and wet conditions. The medium-pore Pd-ZSM-5 zeolite was found to show a much higher C 2 H 4 adsorption capacity than the large-pore Pd-beta and small-pore Pd-SSZ-13 zeolites, despite their similar Si/Al ratios and Pd loadings. Furthermore, during the desorption period, the Pd-ZSM-5 was capable of oxidizing most of the adsorbed C 2 H 4 to CO 2 , revealing its functionality as a catalyzed hydrocarbon trap. The overall characterization results demonstrate that the formation of Pd 2+ ions, which serve as both adsorption and oxidation sites, is more active in Pd-ZSM-5 than Pd-beta and Pd-SSZ-13, rendering it more active as C 2 H 4 trapping. This work led us to suggest that the interaction between Pd ions and zeolite supports is crucial for the C 2 H 4 adsorption and desorption performance in developing HC trap materials