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Abstract: A series of nanosized ZSM‐5 samples was synthesized at 170, 150, 120, and 100 °C. Experimental data show that the decrease of crystallization temperature leads to significant changes in zeolite properties. Crystals synthesized at 100 °C exhibit many framework defects with lower acid‐site density, strength, and a larger external surface area. The selectivity to light olefins and the propylene‐to‐ethylene ratio increases as the crystallization temperature decreases. A propylene‐to‐ethylene ratio of above 6 with the highest selectivity to propylene of 53 % was obtained over ZSM‐5 catalyst prepared at 100 °C. The stability of the nanosized zeolite in methanol to olefins (MTO) was also improved compared to the industrial sample with a similar Si/Al ratio. This catalytic performance is a result of the decrease in the acid‐site density, strength, and the crystals’ size, providing a shorter diffusion path and larger external surface area. The presence of structural defects and a different external surface in the crystals has been shown to play an important role in the MTO catalyst performance. [ABSTRACT FROM AUTHOR]

This study reports the seeded synthesis of MFI‐type (ZSM‐5) zeolite in fluoride medium at pH = 8.5. Crystal growth kinetics of the resulting zeolite (ZSM‐5‐F) as a function of seed content and crystallization temperature is studied. The crystallization time is reduced to 1.5 h and crystals with sizes below 200 nm and a Si/Al ratio of 23.6 are obtained. A zeolite with similar characteristics but synthesized in a hydroxyl medium (ZSM‐5‐OH) is used to evaluate ZSM‐5s synthesized in different crystallization media. Their physicochemical properties are compared and particular attention is paid to the nature, number, and distribution of silanol sites. The two zeolites exhibit similar number of Brφnsted acid sites; however the material synthesized in a hydroxyl medium contains a substantially larger number of surface and internal silanols that impact significantly its catalytic performance in methanol to hydrocarbon transformation. While the two materials exhibit similar selectivity in methanol transformations, the catalyst synthesized in fluoride medium shows superior activity and resistance to deactivation. The results suggest that seeded synthesis in a fluoride medium can be used for the preparation of superior zeolite catalysts. [ABSTRACT FROM AUTHOR]

ZSM-5 zeolite with intra-crystalline mesopores was synthesized via grinding synthesis method (GSM) without any mesoporous templates. It was found that the formation of the mesopores in the ZSM-5 crystals is due to the difference between the speed of crystallization and dissolution processes occurring during the GSM synthesis. The alkalinity of the precursor gels tailored the formation of the mesoporous structure and the crystal size of the ZSM-5 zeolite. The most regular mesopores in the ZSM-5 crystals were formed under grinding synthesis of the precursor gel with a defined concentration of alkali cations (Na 2 O/SiO 2 = 0.113). The size of the mesopores in the ZSM-5 crystals varied from 3 nm to 25 nm, while the size of the individual ZSM-5 crystallites is in the range of 50–300 nm which depend mainly on the amount of NaOH in the precursor gel. Intra-crystalline mesopores are generated in ZSM-5 zeolite only by adjusting NaOH amount during synthesis without extra materials or treatments. Image 1 • Intra-crystalline mesoporous ZSM-5 was prepared by grinding synthesis method without any mesoporous templates. • By regulating NaOH amount in the precursor gel, formation and size of the mesopores could be easily controlled. • The mesopores were generated concurrently with the crystallization of ZSM-5 structure. • Formation of the mesopores was proposed as an imbalance between crystallization and dissolution of crystallites. [ABSTRACT FROM AUTHOR]

FER-type zeolites were synthesized in the presence of Na-Ethylendiamine (Na–En), Na–Pyrrolidine (Na–Py) and Na–K. The crystallization times varied between 96 and 240 h. Ferrierite harvested from the Na–En synthesis was also used as seeds and reduced crystallization time from 240 to 30 h. The product of seeded synthesis was not uniform: nanosized with micronsized crystals as well as complex aggregates of different sizes were obtained. Hierarchical FER-type zeolites were prepared using seeded Na–En synthesized FER as a parent. Secondary pores in zeolite crystals were formed by etching at room temperature with HF-NH 4 F containing solutions, using the HF concentration and treatment time as variables. Crystal morphology and physicochemical characteristics of micron-, nano-sized and hierarchical FER-type crystals were studied by complementary methods including: X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG/dTG), 27 Al and 29 Si MAS NMR, IR spectroscopy of adsorbed probe molecules (Pyridine, Acetonitrile and Lutidine), nitrogen adsorption and chemical analysis. We demonstrate that FER-type zeolites with pre-determined properties can be easily prepared. [ABSTRACT FROM AUTHOR]