Conversion of C8 aromatics over a dual-bed catalyst.

A dual-bed catalyst was prepared for the conversion of C8 aromatics. The upper bed layer consisted of ZSM-5 covered with SiO2, primarily utilized for ethylbenzene dealkylation. By employing tetraethyl orthosilicate (TEOS) as a deposition agent through the chemical liquid deposition (CLD) method, the modified ZSM-5 catalyst exhibited optimal catalytic performance at a TEOS addition of 0.6 g per gram of catalyst. The lower bed layer contained ZSM-39 catalyst, mainly employed for xylene isomerization reaction. ZSM-39 was synthesized using pyrrolidine as the template, and the best catalytic performance was achieved when the OH-/SiO2 molar ratio in the synthesis system was 0.05. The mass ratio between the upper and lower agents was maintained at 1 : 1. Compared to traditional single-bed ZSM-5 catalysts, the dual-bed catalyst demonstrated enhanced activity and selectivity.

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

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.