Liquid-phase xylene isomerization on nano-sized ZSM-5

Abstract

The isomerization process of xylene in the liquid phase has garnered significant attention due to its low energy consumption and high selectivity. However, conventional ZSM-5 zeolites have exhibited significantly diminished activity in this process, primarily attributed to diffusion barriers. To address this issue, Nano-ZSM-5 zeolite was synthesized using tetrapropylammonium hydroxide (TPAOH) as a structure direct agent (SDA) and introducing silicate-1 (S-1) as a crystallization seed. The impact of OH⁻/SiO₂ molar ratio on the sample morphology was investigated. The structure of Nano-ZSM-5 zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ physical -sorption analysis. The results demonstrate that the addition of S-1 crystal seeds enables the formation of ZSM-5 crystallites with diminutive particle sizes (∼20 nm). Furthermore, variations in the OH⁻/SiO₂ molar ratio within the synthetic system impact crystallite aggregation, excessively high or low ratios result in severe aggregation, leading to decreased specific surface area and mesoporous volume. By optimizing the OH⁻/SiO₂ molar ratio to 0.2, the sample exhibits exceptional dispersibility with a specific surface area of 420 m² g⁻¹ and a mesoporous volume extending to 0.57 cm³ g⁻¹. When utilized as a catalyst for liquid-phase xylene isomerization, nano-ZSM-5 demonstrates superior catalytic performance compared to traditional zeolite.