Adsorption of Toluene on Alkali Metal Ion-Exchanged ZSM-5 and β-Zeolites under Humid Conditions

Abstract

Alkali metal ion-exchanged ZSM-5 and β-zeolites were tested as hydrocarbon traps for reducing cold-start emissions. The hydrocarbon trap performances were investigated by temperature-programmed desorption employing toluene as a probe molecule both in the presence and absence of water. Toluene adsorption was significantly inhibited in the presence of water. The extent of this inhibitory effect was strongly dependent on the nature of the alkali metal cation. The Cs cation was the most effective in suppressing the inhibition. The suppression of the inhibition is likely due to an enhancement of the interaction between the toluene molecules and zeolite-framework oxygens bearing high negative charge. Having investigated hydrocarbon trap performances of alkali metal ion-exchanged Y and mordenite zeolites as well as ZSM-5 and β, it was concluded that both the type of alkali metal cation employed and the Si/Al ratio of zeolite were the major factors that affected the hydrocarbon trap performance rather than the nature of framework structure of zeolite. On the other hand, the durability was influenced by the type of framework structure used. The stability decreased in the order: Cs/ZSM-5 > Cs/β > Cs/Y ≈ Cs/mordenite. The adsorption capacity of Cs/ZSM-5 was preserved even after thermal treatment at 900 °C.

Combustion of volatile organic compounds over composite catalyst of Pt/γ-Al2O3and beta zeolite

“…It is clear that toluene molecules are more strongly adsorbed on the Cs + -exchanged beta zeolite than on the protonated beta zeolite, although the amount of toluene adsorbed on the Cs + -exchanged beta zeolite is smaller. [21] No adsorption was observed on γ -Al 2 O 3 . The oxidation of toluene was carried out by replacing the Pt(1%)/mix catalyst with the Pt(1%)Cs + /mix catalyst.…”

“Super Hydrocarbon Reformer Trap” for the Complete Oxidation of Toluene Using Iron‐Exchanged β‐Zeolite with a Low Silicon/Aluminum Ratio

“…At elevated temperatures of the entire system, the adsorbed HCs are desorbed and oxidized by the thermally activated TWC. Zeolites are used frequently as the material for the HC trap because of their strong affinity to HCs and high thermal stability …”

“…To date, various zeolite topologies have been studied as materials for HC traps: ZSM‐5, β‐zeolites, SSZ‐33, MCM‐68, CIT‐1, MOR, FAU, and silicoaluminophosphates (SAPOs) . In these reports, a focus was placed on the adsorption capacity and holding strength of materials (i.e., how long zeolites can retain HCs).…”

“…In these reports, a focus was placed on the adsorption capacity and holding strength of materials (i.e., how long zeolites can retain HCs). Various publications insist that β‐zeolite are more suitable for HC traps than other topologies because it shows a larger adsorption capacity and holds HCs until a higher temperature . In addition, relationships between the zeolitic topology and the adsorption capacity have been also investigated.…”

“…The complete oxidation of trapped HCs into CO 2 was achieved by combining zeolites with a low Si/Al ratio and a large amount of Fe ions (Scheme ). As their high adsorption capacity and strong holding ability have been demonstrated, we selected β‐zeolites as the carriers of Fe ions . Moreover, β‐zeolites synthesized without an organic structure‐directing agent (OSDA) were employed because many groups have claimed that they show a high hydrothermal stability in spite of their high Al content .…”