(292g) A Comparative Study of ZSM-5 and Beta-Zeolites for Hydrocarbon Trap Applications Under “Cold-Start” Conditions

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 methods 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, different acidity 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.  The reactivity of adsorbed propylene on ZSM-5 and beta zeolites were studied by temperature – programmed desorption (TPD) coupled with FTIR and DRIFTS spectroscopic analyses under different mixture conditions containing propylene: neat, H₂O-only, CO₂-only, H₂O+CO₂, and H₂O+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, likely due to competitive adsorption and inhibition of adsorption sites.  The silver exchanged ZSM-5 and β-zeolites - compared to the H⁺counterparts - exhibited an increased storage and desorption of propylene.  In this presentation, we will discuss in detail trends observed between propylene trapping-release performance, zeolite properties, impact of different metals and gas composition.