Adjusting seed solution-assisted synthesis of hierarchical ZSM-5 zeolite to facilitate efficient tetralin cracking

Abstract

The development of mesoporogen-free synthetic routes for hierarchical ZSM-5 zeolites is critical to advancing their application in diffusion-constrained catalytic processes such as heavy oil cracking. Here, we develop a mesoporogen-free strategy through synergistic control of seed solution temperature (70–170 °C) and addition amount (0.8–50 wt%). The synthesized zeolites were characterized using techniques such as X-ray Diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), N₂ adsorption-desorption, ammonia temperature-programmed desorption (NH₃-TPD), and pyridine-infrared (Py-IR). The results show that the sample is rich in mesopores and has well-preserved microporosity. Control experiments under TPAOH conditions equivalent to the seed solution addition amounts and with room-temperature-dried seed solids equivalent to the seed solution were conducted to highlight the critical role of seed solutions. Notably, seed solutions stored for three months retained their effectiveness in synthesizing phase-pure ZSM-5 zeolites, demonstrating exceptional stability. In tetralin (heavy oil model) cracking tests, the optimized zeolite (HZ-T100-A50) achieved 90 % conversion within 2 h, which is 20 % higher than HZ-T100-A0.8, attributed to enhanced reactant accessibility. This study not only provides an eco-friendly method for synthesizing hierarchical ZSM-5 zeolites without mesoporous templates but also deepens the understanding of seed solution impacts, offering an important basis for optimizing zeolites synthesis and application.