Low-temperature synthesis of high-silica ZSM-5 zeolites and their adsorption performance for toluene

Abstract

ZSM-5 is considered to be a promising adsorbent for VOCs, but its adsorption ability in humid environments is not satisfactory due to its strong hydrophilicity. The synthesis of high-silica ZSM-5 molecular sieves with good hydrophobicity and high specific surface area at low temperatures remains a challenge. The advantage of this work lies in the utilization of inexpensive n-butylamine (NBA) as a template and a minimal amount of silicalite-1 as a seed crystal (3%), and the synthesis of high-silica ZSM-5 molecular sieves (SiO₂/Al₂O₃ ratio = 277) with a high specific surface area (409.1 m² g⁻¹) and excellent crystallinity, achieved at a low temperature of 120 °C and a brief crystallization period (24 h). The variables during synthesis are carefully investigated to determine the optimal synthesis conditions. Additionally, the crystallization mechanism for synthesizing high silica ZSM-5 zeolites by synergistic use of NBA and silicalite-1 seed crystals has been proposed. Finally, using toluene as a model molecule, the adsorption performance of the ZSM-5 molecular sieves synthesized at different temperatures was studied under RH = 0 and RH = 50% conditions. The results show that the micropore structure and crystallinity are the most important parameters for toluene adsorption under humid conditions, and should be optimized simultaneously to achieve satisfactory adsorption capacity. The research results will provide guidance for the preparation of hydrophobic adsorbents.