FT-IR spectroscopic studies of hydrocarbon trapping in Ag+-ZSM-5 for gasoline engines under cold-start conditions

A detailed study of adsorption of automobile exhaust hydrocarbons in Ag+-exchanged zeolites under cold-start conditions (room temperature and in the presence of water) was carried out with FT-IR spectroscopy, using toluene and propylene as probes. The results show that exchanged Ag+ in zeolites is unique for trapping olefin and aromatic hydrocarbons due to its resistance to water adsorption. In contrast, exchanged Cu2+ in zeolites, which has good hydrocarbon trapping properties under dry conditions, does not trap hydrocarbons under wet conditions. Here, solvation of Cu2+ screens the interactions of the cation with adsorbed hydrocarbons. The results also show that, in addition to the nature of the cation, the structure of the zeolite also plays a role in hydrocarbon trapping. Aging at high temperatures, with water vapor (∼10%) and SO2 (∼15 ppm), leads to a decrease of the trapping centers in the zeolites due to framework dealumination.