Seeding Bundlelike MFI Zeolite Mesocrystals: A Dynamic, Nonclassical Crystallization via Epitaxially Anisotropic Growth

Direct synthesis by assembly of precursor nanoparticles is a promising strategy for preparing distinct mesoscopic-structured crystals, especially when high controllability is realized. However, uncertain properties of amorphous precursors and inner complicacy of crystallization mechanisms hamper controllable synthesis of zeolite mesocrystals. Here, we develop a salt-aided seed-induced organic-free method to facilely synthesize anisotropic MFI-type nanorod-bundle zeolite mesocrystals. An epitaxial, anisotropic assembly and crystallization of precursor particles on seed crystals is successfully achieved via a distinctively dynamic, nonclassical process, from relatively disordered to ordered attachment (OA), triggering an enhanced one-dimensional (1D) growth, thus constructing a unique core–shell–shell structure. This work sheds new light on the insights of both zeolite mesocrystal properties and a nonclassical crystallization mechanism. With an understanding of the mechanism, this nonclassical process can be exploited to systematically tune mesocrystal properties and create zeolite materials with novel or enhanced physical and chemical performance

Microexplosion under Microwave Irradiation: A Facile Approach to Create Mesopores in Zeolites

A facile microexplosion approach has been successfully developed to produce an interwoven mesopore network in zeolite crystals via the rushing-out of gases generated by decomposition of H₂O₂ under microwave irradiation. This “gas imprint” method creates the mesopores from the interior crystal toward the exterior, in line with the direction of the pristine microporous channels, and is different from the previous methods in which the reagent starts an attack from the crystal surface and perforates inward. The created mesopores extend throughout the whole crystal and highly blend into the intrinsic micropores around. The acidity of zeolite is also well preserved due to this unique mechanism of pore creation. The continuous high quality hierarchical architecture with intact acidity leads to a notable increase both in the conversion of 2-methoxynaphthalene acylation and in the selectivity to the target molecule of 2-acetyl-6-methoxynapthalene. This microexplosion approach offers an efficient synthesis protocol of zeolitic hierarchy integrating intersected mesoporosity and zeolitic microporosity and opens the way to the rational organization of meso- and microporosity for maximal advantage in applications

Dehydration of Glycerol to Acrolein over Hierarchical ZSM‑5 Zeolites: Effects of Mesoporosity and Acidity

Selective dehydration of glycerol to value-added acrolein is an interesting catalytic process not only owing to the increasing coproduction of glycerol in the biodiesel production but also due to the emerging perspectives to provide a sustainable route for acrolein production. The use of zeolites in glycerol dehydration is a very promising way with high performance, but these microporous catalysts are often severely constrained by the rapid catalyst deactivation due to coke formation. Although the introduction of hierarchical structure in microporous zeolite crystals is believed to be an effective approach to enhance their activity and lifetime, the relationship between the mesoporosity and catalytic performance is still controversial. In this paper, four kinds of typical hierarchical ZSM-5 catalysts with diverse mesoporosity and similar microporosity/acidity are prepared by the salt-aided seed-induced route. By systematically studying their catalytic performances, the effects of various mesopore types on the glycerol dehydration are declared, including pore size, amount, distribution, and connectivity. The sample with open and interconnected mesopore architecture display the high activity, long lifetime, and improved selectivity, while the worse behavior of closed and small mesopores is attributed to the mass transfer limitations and/or the in-pore condensation of reactant or its heavier derivatives. Moreover, the combined effect of acidity and hierarchical structure was also explored by changing the framework Si/Al ratio. The findings emphasize the necessity of reasonably designing the zeolite catalysts with proper hierarchical structure and acidity for maximal catalytic advantage