One-pot rota-crystallized hollownest-structured Ti-zeolite: a calcination-free and recyclable catalytic material

Ethanol-assisted synthesis of titanium-rich TS-1 zeolite: a new hexa-coordinated Ti site for efficient propylene epoxidation

TS-1 (MFI) zeolites are widely utilized in various green oxidation reactions, such as alkene epoxidation and alcohol oxidation. To elevate their catalytic efficacy, strategies such as increasing Ti content or constructing highly active Ti species within zeolite are commonly employed. Here, we synthesized a titanium-rich TS-1 zeolite (Si/Ti ratio of 25.6) with an unprecedented hexa-coordinated Ti species, demonstrating high activity in propylene epoxidation, achieved by utilizing ethanol as a crystal growth modifier through a two-step crystallization strategy. The introduced ethanol regulated the crystallization pathway from the classical to the non-classical route, and enhanced the incorporation of Ti within the TS-1 framework by balancing the insertion of Ti and the crystal growth. The hexa-coordinated Ti species promoted by using ethanol as a crystal growth modifier was identified as Ti(OH2)(OSi)3(OSiOH)2 by means of ultraviolet-resonance Raman spectroscopy, X-ray absorption spectroscopy and theoretical calculations, differing from the conventional Ti(H2O)2(OH)2(OSi)2 in TS-1. The as-prepared TS-1 zeolite was applied in the propylene epoxidation reaction, showing exceptional catalytic activity (H2O2 conv. 35.6%), high 1,2-propylene oxide selectivity (93.3%), and excellent stability. This work introduces an ethanol-assisted synthesis strategy that facilitates the incorporation of a new hexa-coordinated Ti species into TS-1 zeolite that is highly active in oxidation reactions.

Polyoxometalate-loaded hyper-crosslinked nanoparticles as a Pickering interfacial catalyst for solvent-free epoxidation of allyl chloride under static conditions

Epoxidation of allyl chloride and hydrogen peroxide (H2O2) carried out in heterogeneous catalytic systems suffer from poor reaction efficiency due to their heavy mass transfer resistance present at the liquid-liquid interface. Pickering interfacial catalysis (PIC) provides an elegant solution by involving the design of amphiphilic heterogeneous catalysts, which can act as emulsifiers simultaneously. In this study, interface-active polyoxometalate-loaded hyper-crosslinked nanoparticles (HCNPs) were designed. The structural properties of materials were characterized in detail by elemental analysis, Zeta potential, ICP-OES, SEM, TEM, BET, FT-IR, TGA, and XPS. The prepared nanoparticles can build efficient W/O PIC systems with allyl chloride and H2O2. Systematic experiments indicate that catalysts' surface properties, catalyst dosage, and water/oil volume ratio significantly affect the PIC system's catalytic activity and emulsion properties. Moreover, this PIC system maintains high stability after the reaction and can be reused for at least 8 cycles. Excitingly, these interface-active HCNPs can also efficiently promote allyl chloride epoxidation in the absence of solvent and external stirring, illustrating that this approach holds great potential for developing catalytic systems suitable for multiphase reactions.

Construction of a One-Dimensional Al-Rich ZSM-48 Zeolite with a Hollow Structure

Diffusion limitation and acid deficiency are two main challenges that the ZSM-48 zeolite faces in practical application. To date, there have been few effective strategies to solve both problems, simultaneously. Also, it is also a challenge to construct a hollow structure in a one-dimensional (1D) zeolite. Herein, an Al-rich ZSM-48 zeolite with a hollow structure is constructed through an alumination-recrystallization strategy, thereby solving the problems related to diffusion and acidity simultaneously. The hollowness and enrichment of aluminum can be controlled by judiciously matching the desilication and recrystallization. The silica to alumina ratio (SAR) of the ZSM-48 zeolite can be tuned from 130 to 45, which breaks the SAR limitation of conventional synthesis. On the basis of the different characterization results, the whole crystallization can be divided into two stages: rapid desilication-alumination and time-consuming recrystallization. In the selective desilication-recrystallization process, the preferential special distribution of the organic template leads to the formation of a hollow structure and the healing of mesopores at the outer shell, as evidenced by structured illumination microscopy images. Due to the enhancement in diffusion ability and acid density, the obtained hollow Al-rich ZSM-48 zeolite exhibits excellent catalytic stability and high p-xylene yield (∼26%) in the m-xylene isomerization reaction (WHSV = 18 h^-1), indicating its strong industrial application potential.

A nucleation-tuned mechanism to prepare centre-crossed zeolite lamellas by the rotating/static switch crystallization strategy

Controllable synthesis of zeolite lamellas with different morphology and property by tuning the nucleation process.

Fast-synthesis and catalytic property of heterogeneous Co-MOF catalysts for the epoxidation of α-pinene with air

A method for synthesizing Co-MOF by rapidly rotating hydrothermal crystallization is proposed. When the rotation speed was 150 rpm, only 2 h was needed to synthesize Co-MOF-150-2 with high catalytic activity and stability.

Highly efficient crystallization of AlPO4-5 accelerated by a rotating hydrothermal synthesis route

Compared with static hydrothermal synthesis, the crystallization rate of an AlPO₄-5 molecular sieve has been accelerated distinctly by a rotating hydrothermal synthesis route with obviously decreased crystal particle size, which is assumed to be ascribed to the increased nucleation centers, accelerated crystal nucleation and growth processes; five-coordinated Al is dominant in the initial reaction gel, and the assembly from amorphous Al species to long-range ordered crystals is mainly contributed by the conversion from five-coordinated Al to four-coordinated Al.

High-Rota Synthesis of Single-/Double-/Multi-Unit-Cell Ti-HSZ Nanosheets To Catalyze Epoxidation of Large Cycloalkenes Efficiently

This work first reports high-efficiency epoxidation of large cycloalkenes (carbon number ≥ 7) with tert-butyl hydroperoxide (TBHP) over single-/double-/multi-unit-cell nanosheet-constructed hierarchical zeolite, which is synthesized by one-step hydrothermal crystallization using piperidine as the structure-directing agent of the microporous structure. The excellent catalytic property of the material is ascribed to its unique structural characteristic. Plenty of surface titanols or silanols on the surface of MWW nanosheets are beneficial for the formation of transition-state intermediates; a large number of intercrystalline mesopores in the shell of the material not only facilitate the formation of the intermediate for TBHP but also have nearly no hindrance for the diffusion and mass transfer of bulky cycloalkene to the above intermediates; the 12-MR side cups penetrating into the crystals from the external surface are exposed as much as possible to the reaction system because of the single-/double-/multi-unit-cell MWW nanosheet, serving as the primary reaction space for the epoxidation of bulky cyclic alkene and oxidants and providing enough space for the transition state of Ti-OO^tBu and bulky cycloalkane. Moreover, an efficient calcination-free catalytic reaction-regeneration method is developed to overcome the challenge for the recyclability of microporous Ti-zeolite in the catalytic epoxidation of bulky cycloalkenes.

A facile organosilane-based strategy for direct synthesis of thin MWW-type titanosilicate with high catalytic oxidation performance

A facile organosilane-based synthetic strategy was successfully developed to prepare thin Ti-MWW zeolite with high catalytic oxidation performance.

Post-synthesis of Zr-MOR as a robust solid acid catalyst for the ring-opening aminolysis of epoxides

Zirconosilicate with the MOR topology (Zr-MOR) was successfully prepared using a two-step post-synthesis strategy from pre-dealumination of a H-MOR zeolite and subsequent dry impregnation of Cp₂ZrCl₂.