Urea-Assisted Two-Step Crystallization Synthesis of Hierarchical Titanium-Rich TS-1 Zeolite

Titanium-rich TS-1 zeolites are highly valued for their catalytic properties. However, its application is often limited by its microporous structure, which restricts the diffusion of larger molecules, resulting in compromised catalytic activity. Additionally, the mismatch between the rates at which titanium and silicon are incorporated into the framework during hydrothermal synthesis remains a big obstacle in achieving optimal titanium loading. This study presents a simple method for preparing Ti-rich, hierarchical, porous TS-1 zeolites by introducing urea as a crystallization modulator in a two-step crystallization process. Characterization techniques, including in situ Fourier transform infrared (FTIR), UV-Raman, X-ray photoelectron spectroscopy (XPS), and electron microscopy, were employed to investigate the crystallization process and the role of urea in enhancing Ti incorporation. The results show that the two-step crystallization effectively creates mesopores and that the introduction of urea significantly increases the framework Ti content while enhancing the mesoporosity. The resulting TS-1 exhibited improved catalytic performance in key reactions, including 1-hexene epoxidation and hydrodesulfurization over NiMo-supported TS-1, compared to conventional TS-1 variants, establishing this method as a promising approach for synthesizing highly efficient titanium-rich zeolites.