Synthesis and characterization of zsm-5 type zeolites

Capturing Different Intermediate Phases during Zeolite Synthesis

Despite extensive efforts over the past several decades, the current mechanistic understanding of zeolite crystallization is still far from satisfactory, thus precluding the synthesis of designer zeolites. Here we show that the nucleation and in situ transformation pathways during the synthesis of medium-pore zeolite TNU-9 can be altered by controlling the extent of cooperative structure direction between Na+ and Cs+ ions in the presence of 1,4-bis(N-methylpyrrolidinium)butane cations as an organic structure-directing agent. The intermediate phase selectivity was found to change from bikitaite to analcime to layered MCM-22 precursor when the gel Na/Cs ratio was adjusted to 7, 15, and 20, respectively. We also show that the transformation of bikitaite into TNU-9 begins at the surface of intermediate crystals, unlike that of analcime and MCM-22 precursor by a dissolution-recrystallization process. The force field simulation results suggest that the nucleation of different intermediate phases is not thermodynamically but kinetically controlled. This study provides a new basis for advancing the fundamental understanding of zeolite crystallization pathways.

Effect of Ga substitution with Al in ZSM-5 zeolite in methanethiol-to-hydrocarbon conversion

The catalytic properties of conventional H-[Al]-ZSM-5 and gallium-substituted H-[Ga]-ZSM-5 were evaluated in the conversion of methanethiol to ethylene (CH₃SH → 1/2C₂H₄ + H₂S). Dimethyl sulfide (DMS), aromatics, and CH₄ were formed as byproducts on the H-[Al]-ZSM-5 catalyst. The introduction of Ga into the ZSM-5 structure provided a high ethylene yield with relatively high selectivity for olefins. Based on the temperature-programmed desorption of NH₃ and pyridine adsorption on zeolites, the strength of acid sites was decreased by introducing Ga into the ZSM-5 structure. Undesirable reactions seemed less likely to occur at weakly acidic sites. The suppression of the formation of dimethyl sulfide (CH₃SH → 1/2C₂H₆S + 1/2H₂S) and the sequential reaction of ethylene to produce aromatics provided a high yield of ethylene over H-[Ga]-ZSM-5.

Mesocrystal morphology regulation by "alkali metals ion switch": Re-examining zeolite nonclassical crystallization in seed-induced process

HYPOTHESIS

It is a Holy Grail to realize the goal-oriented synthesis of zeotype crystals via direct thermodynamic/kinetic control of crystallization in the simplest inorganic system. Especially, the most commonly used counter cations (i.e., Na⁺ and K⁺) are in turn believed to play merely the role of balancing charges and stabilizing frameworks, which make the simple ion-based morphology/porosity control remain big challenges.

EXPERIMENTS

We re-examined the role of Na⁺ and K⁺ to fine-tune the classical/nonclassical crystallization process in a seed-induced system with the simplest composition (Si/Al sources, inorganic alkali, and H₂O), and proposed an "ion switch" strategy. By analyzing the multiple growth curves, tracking the precursor evolution, and observing epitaxial crystallization behavior, a distinctive "ion switch"-worked nonclassical mechanism was uncovered.

FINDINGS

By the "ion switch" strategy, ZSM-5 mesocrystals were fine-regulated with diverse architecture from single crystal to nanocrystallite assembly and intracrystal mesopore-enriched crystal. Such simple ions-controlled crystallization was achieved through microstructure heterogeneity of zeolitic building-blocks triggered by different counterions and their corresponding assembly behavior from oriented attachment to random deposition. Furthermore, this protocol can be extended to a wider H₂O/SiO₂ range, mixed Na⁺/K⁺ systems, and other alkali metal ions from Li⁺ to Cs⁺, and ZSM-5 mesocrystals with extended morphologies can be obtained.

Nanostructured zeolite with brain-coral morphology and tailored acidity: a self-organized hierarchical porous material with MFI topology

Nano-zeolite with brain-coral morphology formed by self-organization of ultra-small nanospheres, exhibits micro/meso porosity with high surface area, distributed acid sites, and reduced diffusion resistance making it a promising solid acid catalyst.

Ultrafast synthesis of zeolites: breakthrough, progress and perspective

An ultrafast route was established to synthesize industrially important zeolites in several minutes, which represents a breakthrough in the field of zeolite synthesis.

Influence of alkalinity on the synthesis of hierarchical LTA zeolite by using bridged polysilsesquioxane

The mechanism of formation of hierarchical LTA zeolite involved the methoxyl groups of bridged polysilsesquioxane hydrolyzing into hydroxyl groups. The Si–O–Si bond was formed between silicon hydroxyl and silica by dehydration, avoiding phase separation.

Ordered Porous Nanomaterials: The Merit of Small

This paper will introduce the reader to some of the “classical” and “new” families of ordered porous materials which have arisen throughout the past decades and/or years. From what is perhaps the best-known family of zeolites, which even now to this day is under constant research, to the exciting new family of hierarchical porous materials, the number of strategies, structures, porous textures, and potential applications grows with every passing day. We will attempt to put these new families into perspective from a synthetic and applied point of view in order to give the reader as broad a perspective as possible into these exciting materials.

Phase selection controlled by sodium ions in the synthesis of FAU/LTA composite zeolite

Zeolite faujasite (FAU), Linde type A (LTA) and FAU/LTA composite have been synthesized using tetramethylammonium cation (TMA⁺) as template, by adjusting only the concentration of Na⁺ ions in the initial solution (1.00 Al₂O₃ 4.36 SiO₂ : 2.39 (TMA)₂ O : β Na₂ O : 249.00H₂ O). Na⁺ ions alter the phase composition of the product more than TMA⁺ or OH^- ions. When Na₂ O concentration [Na₂ O] increases from 0.024 to 0.168, the product gradually changes from pure FAU to pure LTA via the formation of FAU/LTA composite with increasing LTA fraction. Interestingly, the induction periods of FAU and LTA in the FAU/LTA composite zeolite ([Na₂ O] is 0.072) are both 13 h, quite different from the induction periods of their individual pure phases-45 h for FAU and 4 h for LTA. During the crystallization, the LTA/(FAU + LTA) fraction in the composite zeolite decreases in a nearly linear fashion. Scanning electron microscopy, thermogravimetry and differential thermal analysis indicate some difference between the properties of the FAU/LTA composite zeolite and of the mechanical mixture.