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Abstract
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Zeolite adsorbents in automotive hydrocarbon traps are inevitably exposed to hightemperature steam conditions during actual use. K-ZSM-5 zeolites with K+ loadings of 1wt.%, 3wt.%, and 5wt.% were prepared using the isovolumetric impregnation method. The synergistic effects of K+ modification and hydrothermal aging on the hydrocarbon adsorption capacity of ZSM-5 zeolites were investigated through adsorption penetration tests, programmed temperature desorption experiments, and hydrothermal treatment. Experimental results showed that K+ modification enhanced the adsorption capacity of ZSM-5 zeolite for hydrocarbons, prolonged the saturation time for adsorption, and increased the activation energy required for desorption. While the 1wt.% and 3wt.% loaded K-ZSM-5 exhibited superior adsorptiondesorption performance after hydrothermal treatment, K-ZSM-5 loaded with 5wt.% caused pore blockage after hydrothermal aging, thereby restricting the adsorption and diffusion of hydrocarbon molecules. Further studies were conducted using Grand Canonical Monte Carlo (GCMC) simulations to reveal the hydrocarbon adsorption mechanism of ZSM-5 zeolites modified with K+. Simulation results indicated that K+ modification diminishes the Brønsted acidity of the zeolite, which drastically reduces its affinity for water. Furthermore, the K+ ions polarize adsorbate molecules through electrostatic or induced dipole interactions, leading to a selective adsorption preference for CO2 and C4H8.
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