Design of an Organic Template for Synthesizing ITR Zeolites under Ge-Free Conditions.

Germanosilicate zeolites with various structures have been extensively synthesized, but the syntheses of corresponding zeolite structures in the absence of germanium species remain a challenge. One such example is an ITR zeolite structure, which is a twin of the ITH zeolite structure. Through the modification of a classic organic template for synthesizing ITH zeolites and thus designing a new organic template with high compatibility to ITR zeolite assisted by theoretical simulation, we, for the first time, show the Ge-free synthesis of an ITR structure including pure silica, aluminosilicate, and borosilicate ITR zeolites. These materials have high crystallinity, corresponding to an ITR content of more than 95%. In the methanol-to-propylene (MTP) reaction, the obtained aluminosilicate ITR zeolite exhibits excellent propylene selectivity and a long lifetime compared with conventional aluminosilicate ZSM-5 zeolite. The strategy for the design of organic templates might offer a new opportunity for rational syntheses of novel zeolites and, thus, the development of highly efficient zeolite catalysts in the future.

A Six-Membered Ring Molecular Sieve Achieved by a Reconstruction Route.

Zeolite molecular sieves with at least eight-membered rings are widely applied in industrial applications, while zeolite crystals with six-membered rings are normally regarded as useless products due to the occupancy of the organic templates and/or inorganic cation in the micropores that could not be removed. Herein, we showed that a novel six-membered ring molecular sieve (ZJM-9) with fully open micropores could be achieved by a reconstruction route. The mixed gas breakthrough experiments such as CH3OH/H2O, CH4/H2O, CO2/H2O, and CO/H2O at 25 °C showed that this molecular sieve was efficient for selective dehydration. Particularly, a lower desorption temperature (95 °C) of ZJM-9 than that (250 °C) of the commercial 3A molecular sieve might offer an opportunity for saving more energy in dehydration processes.

Recent advances in the synthesis of TS-1 zeolite.

Heteroatomic zeolites as an important class of zeolites, have been widely applied in industrially catalytic processes due to their unique properties. As one of the most representative heteroatomic zeolites, titanosilicate zeolites have been extensively used in the selective oxidations of organic substrates with H2O2 such as cyclohexanone ammoximation, epoxidation of alkenes, and phenol hydroxylation. In this review, recent advances in the synthesis of TS-1 zeolite are briefly summarized, including use of low-cost raw materials (organic templates, silicon, and titanium sources), development of new synthesis routes (post-treatment synthesis, dry-gel conversion synthesis, solvent-free synthesis, and microwave-assisted synthesis), and new strategy for enhanced mass transfer in TS-1 crystals (synthesis of hierarchical and nanosized TS-1 zeolite). This review might help researchers to have a deep understanding on the synthesis of TS-1 zeolite and provide a new opportunity for the design and preparation of highly efficient TS-1 catalysts in the future.

Solvent-free synthesis of FAU zeolite from coal fly ash.

FAU zeolite is successfully synthesized from coal fly ash (CFA) as the sole silicon and aluminum sources under solvent-free conditions. CO2 adsorption and ion-exchange tests show that the product possesses excellent CO2 adsorption capacity and even better Ca2+ and Mg2+ ion exchange capacity, which is particularly important for its wide application in industrial processes.

Targeted synthesis of zeolites from calculated interaction between zeolite structure and organic template.

Zeolites, a class of silica-based porous materials, have been widely employed in the chemical industry for uses such as sorption, separation, catalysis and ion exchange. Normally, the synthesis of zeolites is performed in the presence of organic templates via a trial-and-error route, which is labor-intensive and empirical. In recent years, theoretical simulation from the interaction between a zeolite structure and an organic template has been used to guide the synthesis of zeolites, which is time-saving. In this review, recent progress in the targeted synthesis of zeolites from interaction between a zeolite structure and an organic template are briefly outlined including the design of new templates for zeolite synthesis, preparation of zeolites with new composition, development of novel routes for zeolite synthesis, synthesis of intergrowth zeolites, generation of novel zeolite structures, control of zeolite morphology and modulation of aluminum distribution in zeolites. These targeted syntheses reveal that the minimum energy principle from the theoretical simulation is key for guiding zeolite crystallization. This review will be important for zeolite researchers for rationally synthesizing zeolites and effectively designing new zeolite structures.

Design of a Small Organic Template for the Synthesis of Self-Pillared Pentasil Zeolite Nanosheets.

Zeolite nanosheets with excellent mass transfer are attractive, but their successful syntheses are normally resulted from a huge number of experiments. Here, we show the design of a small organic template for the synthesis of self-pillared pentasil (SPP) zeolite nanosheets from theoretical calculations in interaction energies between organic templates and pentasil zeolite skeletons. As expected, the SPP zeolite nanosheets with the thickness at 10-20 nm have been synthesized successfully. Characterizations show that the SPP zeolite nanosheets with about 90% MFI and 10% MEL structures have good crystallinity, the house-of-card morphology, large surface area, and fully four-coordinated aluminum species. More importantly, methanol-to-propylene tests show that the SPP zeolite nanosheets exhibit much higher propylene selectivity and longer reaction lifetime than conventional ZSM-5 zeolite. These results offer a good opportunity to develop highly efficient zeolite catalysts in the future.

Zeolite nanosheets for catalysis.

Zeolites with well-defined micropores have been widely used as heterogeneous catalysts in the fields of petroleum refining, fine chemicals, and environment protection. However, the sole micropores in the zeolite structures usually impose diffusion constraints, which would greatly influence their catalytic performances. Therefore, it is highly desirable to shorten the diffusion pathway of zeolites and thus eliminate the diffusion constraints. One of the efficient methods is to synthesize zeolite nanosheets, which has become a hot topic in the past decades. In this tutorial review, the recent progresses in the synthesis of zeolite nanosheets and their relevant catalysis are briefly discussed. Various strategies for the synthesis of zeolite nanosheets are summarized including delamination, templated crystallization, additive-assisted synthesis, seed-directed synthesis, and gaseous expansion synthesis. In addition, the catalytic reactions of zeolite nanosheets with acidic and metal sites are also outlined. This tutorial review should be significant for the design and preparation of highly efficient zeolite catalysts.

A Carbonylation Zeolite with Specific Nanosheet Structure for Efficient Catalysis.

Up to now, the member of zeolite family has expanded to more than 230. However, only little part of them have been reported as catalysts used in reactions. Discovering potential zeolites for reactions is significantly important, especially in industrial applications. A carbonylation zeolite catalyst Al-RUB-41 has special morphology and channel orientation. The 8-MR channel of Al-RUB-41 is just perpendicular to its thin sheet, making a very short mass-transfer distance along 8-MR. This specific nature endows Al-RUB-41 with efficient catalytic ability to dimethyl ether carbonylation reaction with beyond 95% methyl acetate selectivity. Compared with the most widely accepted carbonylation zeolite catalysts, Al-RUB-41 behaves a much better catalytic stability than H-MOR and a greatly enhanced catalytic activity than H-ZSM-35. A space-confined deactivation mechanism over Al-RUB-41 is proposed. By erasing the acid sites on outer surface, Al-RUB-41@SiO2 catalyst achieves a long-time and high-efficiency activity without any deactivation trend.

A Cationic Oligomer as an Organic Template for Direct Synthesis of Aluminosilicate ITH Zeolite.

There are a large number of zeolites, such as ITH, that cannot be prepared in the aluminosilicate form. Now, the successful synthesis of aluminosilicate ITH zeolite using a simple cationic oligomer as an organic template is presented. Key to the success is that the cationic oligomer has a strong complexation ability with aluminum species combined with a structural directing ability for the ITH structure similar to that of the conventional organic template. The aluminosilicate ITH zeolite has very high crystallinity, nanosheet-like crystal morphology, large surface area, fully four-coordinated Al species, and abundant acidic sites. Methanol-to-propylene (MTP) tests reveal that the Al-ITH zeolite shows much higher selectivity for propylene and longer lifetime than commercial ZSM-5. FCC tests show that Al-ITH zeolite is a good candidate as a shape-selective FCC additive for enhancing propylene and butylene selectivity.

Direct Synthesis of Aluminosilicate IWR Zeolite from a Strong Interaction between Zeolite Framework and Organic Template.

A large amount of zeolite structures are still not synthetically available or not available in the form of aluminosilicate currently. Despite significant progress in the development of predictive concepts for zeolite synthesis, accessing some of these new materials is still challenging. One example is the IWR structure as well. Despite successful synthesis of Ge-based IWR zeolites, direct synthesis of aluminosilicate IWR zeolite is still not successful. In this report we show how a suitable organic structure directing agent (OSDA), through modeling of an OSDA/zeolite cage interaction, could access directly the aluminum-containing IWR structure (denoted as COE-6), which might allow access to new classes of materials and thus open opportunities in valuable chemical applications. The experimental results reveal that the COE-6 zeolites with a SiO2/Al2O3 ratio as low as 30 could be obtained. Very interestingly, the COE-6 zeolite has much higher hydrothermal and thermal stabilities than those of the conventional Ge-Al-IWR zeolite. In methanol-to-propylene (MTP) reaction, the COE-6 zeolite exhibits excellent selectivity for propylene, offering a potential catalyst for MTP reaction in the future.

Forward transmission characteristics in polystyrene solution with different concentrations by use of circularly and linearly polarized light.

Polarized light forward propagation in scattering environments is important basic research. Polystyrene microspheres in water are common scattering environments that can be helpful to investigate in existing literature research. In this paper, we investigated the polarization state persistence of both linearly and circularly polarized light. We used a single active source with a wavelength of 532 nm to illuminate 1 µm diameter polystyrene spheres immersed in water. To evaluate the polarization state persistence of linearly and circularly polarized light, a parameter change of polarization state was used to replace the Stokes parameters. In the setting environments of different concentrations, circularly polarized light has superior polarization state persistence to that of linearly polarized light.

Sustainable Synthesis of Pure Silica Zeolites from a Combined Strategy of Zeolite Seeding and Alcohol Filling.

Currently, the synthesis of pure silica zeolites always requires the presence of organic structure-directing agents (OSDAs), which direct the assembly pathway and ultimately fill the pore space. A sustainable route is now reported for synthesizing pure silica zeolites in the absence of OSDAs from a combined strategy of zeolite seeding and alcohol filling, where the zeolite seeds direct crystallization of zeolite crystals from amorphous silica, while the alcohol is served as pore filling in the zeolites. Very importantly, the alcohol could be fully washed out from zeolite pores by water at room temperature, which completely avoids calcination at high temperature for removal of OSDAs in the synthesis of pure silica zeolites.

Direct Synthesis of Aluminosilicate SSZ-39 Zeolite Using Colloidal Silica as a Starting Source.

For the first time, SSZ-39 zeolite has been directly prepared using conventional colloidal silica and sodium aluminate instead of using FAU zeolite as the raw material in the alkaline media. The adjustment of the Si/Al ratios in the starting materials to the suitable values is a key factor to prepare the aluminosilicate SSZ-39 zeolite. Various characterizations (for instance, X-ray diffraction, scanning electron microscopy, nitrogen sorption, solid 27Al NMR, and NH3-temperature-programmed desorption) display that the aluminosilicate SSZ-39 zeolite owns high crystallinity, uniform cuboid morphology, large surface area, four-coordinated aluminum species, and strong acidic sites. Inductively coupled plasma analysis shows that the SiO2/Al2O3 ratios of the SSZ-39 products are ranged from 12.8 to 16.8. Considering the special framework of the SSZ-39 zeolite, the yield of this synthesis is not higher than 21.3%. Moreover, the catalytic performance of Cu-SSZ-39 catalyst synthesized from this route is excellent in the selective catalytic reduction of NO x with NH3 (NH3-SCR).

Cost-effective mid-infrared micropolarizer fabricated on common silicon by soft nanoimprint lithography.

We fabricated a cost-effective mid-IR micropolarizer on a common Si substrate. To improve the transmittance of Si, we performed a double oxidation on the silicon substrate. The SiO2-Si-SiO2 structure improved the transmittance of Si from 54% to 63%-83%. Then, the mid-IR micropolarizer with multidirectional gratings was fabricated using a soft nanoimprint process followed by the thermal evaporation of Al. Experimental measurements showed a transverse magnetic transmittance in the range of 61%-80% at wavelengths of 4-5 µm, and the extinction ratio was greater than 19 dB.

Design Synthesis of ITE Zeolite Using Nickel-Amine Complex as an Efficient Structure-Directing Agent.

Modern methodologies for synthesizing zeolites typically involve the employment of costly organic structure-directing agents. Herein, we report the design synthesis of aluminosilicate zeolite with ITE structure using an inexpensive nickel-amine complex (nickel-pentaethylenexamine) as a novel structure-directing agent. Characterizations including X-ray diffraction, scanning electron microscopy, N2 sorption isotherms, and 27Al magic-angle spinning NMR techniques show that the ITE zeolite has high crystallinity, perfect crystals, large surface area, and abundant aluminum species in the framework. More importantly, catalytic tests on the hydrogenation of CO2 into methane show that the Ni-ITE zeolite exhibits better catalytic performance than aluminosilicate-supported and silica-supported nickel catalysts. Obviously, the use of nickel-amine complex offers an alternative and facile way to synthesize aluminosilicate zeolites.

Solvent-Free Synthesis of Zeolites: Mechanism and Utility.

Zeolites have been extensively studied for years in different areas of chemical industry, such as shape selective catalysis, ion-exchange, and gas adsorption and separation. Generally, zeolites are prepared from solvothermal synthesis in the presence of a large amounts of solvents such as water and alcohols in sealed autoclaves under autogenous pressure. Water has been regarded as essential to synthesize zeolites for fast mass transfer of reactants, but it occupies a large space in autoclaves, which greatly reduces the yield of zeolite products. Furthermore, polluted wastes and relatively high pressure due to the presence of water solvent in the synthesis also leads to environmental and safety issues. Recently, inspired by great benefits of solvent-free synthesis, including the environmental concerns, energy consumption, safety, and economic cost, researchers continually challenge the rationale of the solvent and reconsider the age-old question "Do we actually need solvents at all in zeolite synthesis?" In this Account, we briefly summarize our efforts to rationally synthesize zeolites via a solvent-free route. Our research demonstrates that a series of silica, aluminosilicate, and aluminophosphate-based zeolites can be successfully prepared by mixing, grinding, and heating starting solid materials under solvent-free conditions. Combining an organotemplate-free synthesis with a solvent-free approach maximizes the advantages resulting in a more sustainable synthetic route, which avoids using toxic and costly organic templates and the formation of harmful gases by calcination of organic templates at high temperature. Furthermore, new insights into the solvent-free crystallization process of zeolites have been provided by modern techniques such as NMR and UV-Raman spectroscopy, which should be helpful in designing new zeolite structures and developing novel routes for synthesis of zeolites. The role of water and the vital intermediates during the crystallization of zeolites have been proposed and verified. In addition to a significant reduction in liquid wastes and a remarkable increase in zeolite yields, the solvent-free synthesis of zeolites exhibits more unprecedented benefits, including (i) the formation of hierarchical micro-, meso-, and macrostructures, which benefit the mass transfer in the reactions, (ii) rapid synthesis at higher temperatures, which greatly improve the space-time yields of zeolites, and (iii) construction of a novel catalytic system for encapsulation of metal nanoparticles and metal oxide particles within zeolite crystals synergistically combining the advantages of catalytic metal nanoparticles and metal oxide particles (high activity) and zeolites (shape selectivity). We believe that the concept of "solvent-free synthesis of zeolites" would open a door for deep understanding of zeolite crystallization and the design of efficient zeolitic catalysts.

Design and preparation of efficient hydroisomerization catalysts by the formation of stable SAPO-11 molecular sieve nanosheets with 10-20 nm thickness and partially blocked acidic sites.

SAPO-11 nanosheets with partially filled micropores (N-SAPO-11) and a thickness of 10-20 nm were synthesized using polyhexamethylene biguanide hydrochloride (PHMB) as a mesoporogen and di-n-propylamine (DPA) as a microporous template. After Pt loading (0.5 wt%), the Pt/N-SAPO-11 catalyst exhibits higher selectivity for the isomers and lower selectivity for cracking products than conventional Pt/SAPO-11 catalysts in the hydroisomerization of n-dodecane.

Atom-economical synthesis of a high silica CHA zeolite using a solvent-free route.

A high silica CHA zeolite is successfully synthesized in the presence of a small amount of N,N,N-dimethylethylcyclohexylammonium bromide under solvent-free conditions. Catalytic tests for the selective catalytic reduction of NOx with NH3 (NH3-SCR) and methanol-to-olefins (MTO) show that the sample from the solvent-free route exhibits comparable catalytic properties to that from the conventional route.

Solvent-Free Synthesis of Zeolite Crystals Encapsulating Gold-Palladium Nanoparticles for the Selective Oxidation of Bioethanol.

The conversion of bioethanol into valuable products is an important area in the conversion of biomass. We demonstrate the successful synthesis of bimetallic gold-palladium (Au-Pd) nanoparticles encapsulated within S-1 zeolite crystals (AuPd@S-1) by a solvent-free strategy. This strategy allows highly efficient use of the noble metals, with more than 96 % of the gold and palladium being loaded into the final samples. Electron microscopy characterization and investigations with probe molecules confirm that the Au-Pd nanoparticles are encapsulated inside the S-1 crystals. The AuPd@S-1 catalyst is very active for the aerobic oxidation of bioethanol, giving 100 % conversion and 99 % selectivity to acetic acid. Even in the presence of 90 % water, the catalyst still gives a conversion higher than 80 % and a selectivity of 95 %. More importantly, the AuPd@S-1 catalyst exhibits excellent stability in the oxidation of bioethanol. These features are important for future practical applications of the AuPd@S-1 catalyst.

Solvent-free synthesis of zeolites from anhydrous starting raw solids.

Development of sustainable routes for synthesis of zeolites is very important because of wide applications of zeolites at large scale in the fields of catalysis, adsorption, and separation. Here we report a novel and generalized route for synthesis of zeolites in the presence of NH4F from grinding the anhydrous starting solid materials and heating at 140-240 °C. Accordingly, zeolites of MFI, BEA*, EUO, and TON structures have been successfully synthesized. The presence of F(-) drives the crystallization of these zeolites from amorphous phase. Compared with conventional hydrothermal synthesis, the synthesis in this work not only simplifies the synthesis process but also significantly enhances the zeolite yields. These features should be potentially of great importance for industrial production of zeolites at large scale in the future.