Two-step dealumination-silanization enhances toluene adsorption-desorption of high-silica ZSM-5 under high humidity

ZSM-5 zeolite adsorbents exhibit limited adsorption capacity for volatile organic compounds (VOCs) under high-humidity conditions, constraining their industrial applicability. In this study, a series of hierarchical ZSM-5 zeolites with high silica-to-alumina ratios (SARs) were successfully prepared via a facile acid pretreatment followed by surface methyl grafting. Using toluene as a representative VOC, the adsorption and desorption properties of these samples were assessed through dynamic adsorption breakthrough curves and temperature-programmed desorption (TPD) experiments. It was found that the two-step modification significantly enhanced both the breakthrough time and saturation adsorption capacity of high-SAR ZSM-5 for toluene in the presence of water vapor. AHFS-TZ5 and HCl-TZ5 exhibited superior performance, showing 53.9 % and 59.5 % enhancements in breakthrough time over ZSM-5, respectively. Specifically, the toluene adsorption capacity of AHFS-TZ5 under humid conditions (4 vol% H 2 O) reached 67.38 mg·g −1 , approximately 1.47 times higher than that of the unmodified ZSM-5. However, the hydrophobic -CH 3 groups grafted onto the ZSM-5 surface moderately hindered toluene diffusion due to increased steric hindrance. Additionally, AHFS-TZ5 exhibited excellent regeneration ability after desorption at 180 ºC, retaining 95 % of its initial adsorption capacity. This study provided a promising approach for preparing hydrophobic zeolites, offering a potential solution for efficient VOC adsorption in high-humidity flue gas environments.