A Comparative Study of ZSM-5 and β-Zeolites for Hydrocarbon Trap Applications under “Cold-Start” Conditions
Eleni Kyriakidou, Oak Ridge National Labolatory
A Comparative Study of ZSM-5 and β-Zeolites for Hydrocarbon Trap Applications under “Cold-Start†Conditions
Eleni A. Kyriakidou, Jae-Soon Choi*, Mi-Young Kim, Todd J. Toops, and James E Parks II
Oak Ridge National Laboratory, Oak Ridge, TN, USA
*choijs@ornl.gov
Emission legislation for vehicle pollutants is becoming more stringent worldwide due to increasing concerns of the impact of air pollution on both the environment and public health. Significant attention has been paid to develop a method to treat automobile exhausts for the regulated emissions such as hydrocarbons during the engine cold start. An effective solution is to employ suitable porous materials which can trap and retain hydrocarbons temporarily until automotive emission control catalysts are lit off. For this purpose, zeolites have been found to be a preferred type of adsorbent materials due to their thermal stability and affinity to HCs. In this work, ZSM-5 and β-zeolites, were studied using a laboratory reactor as hydrocarbon traps under simulated cold-start emission conditions. Propylene was used as a model HC compound. Adsorption and TPD tests were performed under four different mixture conditions containing propylene: H2O/CO2, CO2, H2O and NO. The results demonstrated the high performance of ZSM-5 and β-zeolites in the absence of H2O and CO2. However, the amount of propylene adsorbed on ZSM-5 zeolite significantly decreased in the presence of water in the feed gas stream, mainly due to the hydrophobicity of the catalyst surface. The silver exchanged ZSM-5 and β-zeolites – compared to the H+ counterparts – exhibited an increased storage and desorption of propylene. Moreover, the presence of NO over the Ag-ZSM-5 catalyst showed no affect onto propylene adsorption/desorption. In this presentation, we will discuss in detail trends observed between propylene trapping-release performance, zeolite properties, and gas composition.
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