In Situ Synthesis of Zn/Silicalite-1 via Subcrystals: Constructing a Framework with Abundant Weak Acid Sites and High Stability

Abstract

This study focuses on developing effective methods for incorporating Zn species into the Silicalite-1 zeolite framework, leveraging the open structure of MFI zeolite subcrystals, to enhance its acidic properties for broader catalytic applications. This study developed a Zn-modified Silicalite-1 zeolite (ZnS-1-Sc) with enhanced acidic properties via the subcrystals in situ method. The ZnS-1-Sc showed a 3.9-fold increase in weak acid sites compared to unmodified Silicalite-1, confirmed by NH₃-TPD and Py-IR. It also maintains a complete framework structure to exhibit excellent stability and hydrothermal stability, which was determined by UV–vis, XPS, FT-IR, ²⁹Si MAS SSNMR and the hydrothermal stability test. In synthesizing pyridine bases, ZnS-1-Sc outperformed traditional HZSM-5, maintaining over 15% yield after 20 h versus less than 10% yield in 9 h. This study not only provides a new strategy for the metal modification of Silicalite-1 zeolite but also provides an important reference for the metal modification of other zeolite materials.