Crystallization Behavior of Highly Defective MSE-Type Zeolite, Incorporation of Ti into the Framework, and Its Hydrophobic–Hydrophilic Nature Controlled by Post-Synthesis Modifications

YNU-2 is a pure-silica version of MSE-type zeolite obtained by steam-assisted crystallization (SAC) technique, followed via suitable stabilization by postsynthesis modification. Taking advantage of the SAC method, the change of zeolitic phase during the crystallization was tracked. In the presence of organic structure-directing agent (OSDA), the Beta phase first appeared as an intermediate followed by the formation of OSDA-MSE composite, YNU-2P, as the final crystallization product. When the YNU-2P was directly calcined at temperatures higher than 400 °C to remove the occluded OSDA, the MSE framework collapsed due to the existence of a large number of site defects in the framework. The highly crystalline YNU-2 was only obtained when the YNU-2P was steamed or acid-treated under appropriate conditions. The framework stabilization was achieved by various techniques that cause Si-migration. The extent of Si-migration was dependent on the treatment conditions. For the Ti-incorporation to prepare [Ti]-YNU-2, enough but incomplete Si-migration by steaming is necessary rather than thorough acid-treatment to fill all the site defects. [Ti]-YNU-2 exhibits a catalytic performance superior to that of [Ti]-MCM-68, even though the former has a local hydrophilic field in the micropores that gives a type-V water adsorption isotherm, suggesting that the Si-migration occurs during the steaming and generates hydrophilic supermicropores

Ti-YNU-2: A Microporous Titanosilicate with Enhanced Catalytic Performance for Phenol Oxidation

YNU-2P, a highly crystalline composite of organic structure-directing agent and pure-silica MSE precursor, was stabilized by steaming so as to retain adequate site defects. To the remaining site defects, the efficient introduction of Ti into the framework was accomplished to give the new microporous titanosilicate Ti-YNU-2 after optimizing the conditions for steaming and vapor phase TiCl₄ treatments. This material proved to be a high-performance catalyst, exhibiting remarkably enhanced performance compared to Ti-MCM-68, a material already known to show superior performance to TS-1, during phenol oxidation using H₂O₂ as an oxidant

Mechanochemical Approach for Selective Deactivation of External Surface Acidity of ZSM‑5 Zeolite Catalyst

The acid sites associated with the external surface of zeolite particles are responsible for undesirable consecutive reactions, such as isomerization, alkylation, and oligomerization, resulting in a lower selectivity to a target product; therefore, the selective modification (deactivation) of the external surface of zeolite particles has been an important issue in zeolite science. Here, a new method for surface deactivation of zeolite catalyst was tested via a mechanochemical approach using powder composer. Postsynthetic mechanochemical treatment of ZSM-5 zeolite causes a selective deactivation of catalytically active sites existing only on the external surface, as a potentially useful catalyst for highly selective production of <i>p</i>-xylene

Correction to “A Microporous Aluminosilicate with 12‑, 12‑, and 8‑Ring Pores and Isolated 8‑Ring Channels”

Correction to “A Microporous Aluminosilicate with 12‑, 12‑, and 8‑Ring Pores and Isolated 8‑Ring Channels

A Microporous Aluminosilicate with 12‑, 12‑, and 8‑Ring Pores and Isolated 8‑Ring Channels

Synthesis of new zeolites with controlled pore architectures is important in the field of catalysis and separation related to chemical transformation, environmental protection, and energy-saving. Zeolites containing channels of different sizes in the same framework have been desirable. We report here the synthesis and structure of a novel aluminosilicate zeolite (designated as YNU-5), the first zeolite containing interconnected 12-, 12-, and 8-ring pores, as well as independent straight 8-ring channels. The synthesis procedure is quite simple and consists of conventional hydrothermal conditions as well as readily available starting materials. The framework structure is stable enough and Si/Al ratio is controllable between 9 and 350. Determination of the crystal structure is performed by utilizing X-ray diffraction-based techniques, revealing 9 independent tetrahedrally coordinated atoms. This robust structure is expected to be industrially valuable and several unusual combinations of composite building units are of considerable interest in an academic sense. The new zeolite YNU-5 is promising catalyst for the production of useful light olefins such as propylene and butylenes in the dimethyl ether-to-olefin reaction, when the Si/Al ratio is properly tuned by dealumination through simple acid treatments

A Microporous Aluminosilicate with 12‑, 12‑, and 8‑Ring Pores and Isolated 8‑Ring Channels

Synthesis of new zeolites with controlled pore architectures is important in the field of catalysis and separation related to chemical transformation, environmental protection, and energy-saving. Zeolites containing channels of different sizes in the same framework have been desirable. We report here the synthesis and structure of a novel aluminosilicate zeolite (designated as YNU-5), the first zeolite containing interconnected 12-, 12-, and 8-ring pores, as well as independent straight 8-ring channels. The synthesis procedure is quite simple and consists of conventional hydrothermal conditions as well as readily available starting materials. The framework structure is stable enough and Si/Al ratio is controllable between 9 and 350. Determination of the crystal structure is performed by utilizing X-ray diffraction-based techniques, revealing 9 independent tetrahedrally coordinated atoms. This robust structure is expected to be industrially valuable and several unusual combinations of composite building units are of considerable interest in an academic sense. The new zeolite YNU-5 is promising catalyst for the production of useful light olefins such as propylene and butylenes in the dimethyl ether-to-olefin reaction, when the Si/Al ratio is properly tuned by dealumination through simple acid treatments

A Microporous Aluminosilicate with 12‑, 12‑, and 8‑Ring Pores and Isolated 8‑Ring Channels

Synthesis of new zeolites with controlled pore architectures is important in the field of catalysis and separation related to chemical transformation, environmental protection, and energy-saving. Zeolites containing channels of different sizes in the same framework have been desirable. We report here the synthesis and structure of a novel aluminosilicate zeolite (designated as YNU-5), the first zeolite containing interconnected 12-, 12-, and 8-ring pores, as well as independent straight 8-ring channels. The synthesis procedure is quite simple and consists of conventional hydrothermal conditions as well as readily available starting materials. The framework structure is stable enough and Si/Al ratio is controllable between 9 and 350. Determination of the crystal structure is performed by utilizing X-ray diffraction-based techniques, revealing 9 independent tetrahedrally coordinated atoms. This robust structure is expected to be industrially valuable and several unusual combinations of composite building units are of considerable interest in an academic sense. The new zeolite YNU-5 is promising catalyst for the production of useful light olefins such as propylene and butylenes in the dimethyl ether-to-olefin reaction, when the Si/Al ratio is properly tuned by dealumination through simple acid treatments

Facile Fabrication of ZSM‑5 Zeolite Catalyst with High Durability to Coke Formation during Catalytic Cracking of Paraffins

Post-synthetic HNO₃ treatment of ZSM-5 zeolite synthesized in the absence of organic structure-directing agent removes framework Al selectively from the external surface, producing a unique ZSM-5 zeolite catalyst that has very few acid sites on its external surfaces. The resulting external acid sites can be readily deactivated at the early stage of the reaction, giving a potentially long-life catalyst as a result of a high durability to coke formation during the cracking of hexane or other paraffin molecules

Effective Fabrication of Catalysts from Large-Pore, Multidimensional Zeolites Synthesized without Using Organic Structure-Directing Agents

An Al-rich zeolite beta with *BEA topology and a Si/Al ratio as low as 6–7 was synthesized without the use of an organic structure-directing agent (OSDA) and subsequently treated by steam followed by heating with nitric acid for the purposes of dealumination, so as to prepare a catalyst. The steaming process played an important role in stabilizing the *BEA framework, presumably by repairing site defects with migrating silicon species. Steaming at around 700 °C was observed to produce optimal stabilization of the zeolite and allowed subsequent acidic dealumination while maintaining an intact framework. A second demonstration of successful OSDA-free synthesis and effective catalyst fabrication through postsynthetic modification involved the fabrication of a 12–10–10-ring zeolite having an MSE-type framework. This represented the first successful synthesis of an Al-rich MSE-type zeolite (with a Si/Al ratio as low as 6–7) using seed crystals in the absence of any OSDA. The gel composition as well as the crystallization temperature and time were optimized for the purpose of this synthesis such that a pure MSE phase could be obtained in a relatively short crystallization period of only 45 h. Longer crystallization periods and inadequate aging times gave mordenite as an impurity and as a major phase, respectively. These results offer further support for the so-called “composite building unit” hypothesis. As with the zeolite beta, direct dealumination of the MSE-type zeolite by acid treatment resulted in the collapse of the framework, which was avoided by steaming at 700 °C. After stabilization by steaming, acidic dealumination without framework collapse became possible. The dealuminated versions of the Al-rich beta and MSE-type zeolites were shown to be effective catalysts for the hexane cracking reaction, affording propylene in high selectivity. The MSE-type zeolite exhibited a particularly high level of coking resistance in addition to a significant yield of propylene, indicating that zeolites synthesized without using an OSDA show promise for industrial applications as highly selective and long-lived catalysts

Top-Down Tuning of Nanosized ZSM-5 Zeolite Catalyst by Bead Milling and Recrystallization

Zeolites with high external surface area allow diffusing reactants greater access to catalytically active sites, which has led to interest in the preparation of nanosized zeolites. In this study, a top-down approach has been used for zeolite synthesis by first milling the zeolite to produce nanoparticles. This technique destroys the outer portion of the zeolite framework, causing a significant decrease in its catalytic activity. To remedy this, the damaged part was recrystallized using a dilute silicate solution after bead milling. The combined bead milling and postmilling recrystallization yielded nano ZSM-5 (MFI type zeolite), approximately 60 nm in size, with high crystallinity, and the zeolite powder showed a higher catalytic activity in cumene cracking in comparison with the raw ZSM-5 zeolite. Furthermore, the decrease in crystal size suppresses catalyst deactivation through coke deposition during cumene cracking