One-step synthesis of hierarchical-structured ZSM-5 zeolite

Generally, the process for synthesis of hierarchical-structured ZSM-5 zeolite is complex. Here, the polygonal three-dimensional ZSM-5 zeolite with hierarchical structure was hydrothermally synthesized by one-step synthesis method with dual templates. The effects of crystallization conditions and synthesis gel compositions, including crystallization temperature, crystallization time, Si/Al molar ratio, on the products were investigated for optimizing synthesis conditions. The X-ray diffraction (XRD), N₂ adsorption-desorption experiment, Pyridine adsorption FT-IR (Py-FTIR), scanning electron microscopy (SEM) and transmission electron microscope (TEM) were used to characterize the crystalline structure, pore structure, surface acidity and crystal morphology of products. It was shown that the hierarchical-structured ZSM-5 zeolite can be synthesized under the following conditions: crystallization temperature of 160-180℃, crystallization time of 24-96 h, the SiO₂/Al₂O₃/Na₂O/CTAB/TPABr/H₂O ratio of 1/x/0.4/0.05/0.12/280, (x: 50-240). The sample crystallized at 160℃ for 48 h with a synthesis gel having a Si/Al molar ratio of 50 had uniform cylindrical crystal morphology, high crystallinity and ordered mesoporous structure with a pore diameter of 3.60 nm. It contains both strong Brønsted and Lewis acid sites at 300℃, which contribute to its catalytic properties.