15 research outputs found

    One-Pot Synthesis of Alumina-Titanium Diboride Composite Powder at Low Temperature

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    Alumina-titanium diboride (Al2O3-TiB2) composite powders were synthesised via aluminothermic reduction of TiO2 and B2O3, mediated by a molten chloride salt (NaCl, KCl, or MgCl2). The effects of salt type, initial batch composition, and firing temperature/time on the phase formation and overall reaction extent were examined. Based on the results and equilibrium thermodynamic calculations, the mechanisms underpinning the reaction/synthesis processes were clarified. Given their evaporation losses at test temperatures, appropriately excessive amounts of Al and B2O3 are needed to complete the synthesis reaction. Following this, phase-pure Al2O3-TiB2 composite powders composed of 0.3–0.6 μm Al2O3 and 30–60 nm TiB2 particles were successfully fabricated in NaCl after 5 h at 1050 °C. By increasing the firing temperature to 1150 °C, the time required to complete the synthesis reaction could be reduced to 4 h, although the sizes of Al2O3 and TiB2 particles in the resultant phase pure composite powder increased slightly to 1–2 μm and 100–200 nm, respectively

    Enhanced Trace Carbon Dioxide Capture on Heteroatom-Substituted RHO Zeolites under Humid Conditions

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    Boron and copper heteroatoms were successfully incorporated into the frameworks of high-silica RHO zeolite by adopting a bulky alkali-metal-crown ether (AMCE) complex as the template. These heteroatom-doped zeolites show both larger micropore surface areas and volumes than those of their aluminosilicate analogue. Proton-type RHO zeolites were then applied for the separation of CO2/CH4/N-2 mixtures, as these zeolites have weaker electric fields and, thus, lower heats of adsorption. The adsorption results showed that a balance between working capacity and adsorption heat could be achieved for these heteroatom-doped zeolites. Ideal adsorbed solution theory predictions indicate that these zeolites should have high selectivities even for remarkably dilute sources of CO2. Finally, the heteroatom-substituted zeolites, especially the boron-substituted one, could be thermally regenerated rapidly at 150 degrees C after full hydration and maintained high regenerability for up to 30 cycles; therefore, they are potential candidates for trace CO2 removal under humid conditions

    Covalent Organic Frameworks with Ionic Liquid-Moieties (ILCOFs): Structures, Synthesis, and CO2 Conversion

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    CO2, an acidic gas, is usually emitted from the combustion of fossil fuels and leads to the formation of acid rain and greenhouse effects. CO2 can be used to produce kinds of value-added chemicals from a viewpoint based on carbon capture, utilization, and storage (CCUS). With the combination of unique structures and properties of ionic liquids (ILs) and covalent organic frameworks (COFs), covalent organic frameworks with ionic liquid-moieties (ILCOFs) have been developed as a kind of novel and efficient sorbent, catalyst, and electrolyte since 2016. In this critical review, we first focus on the structures and synthesis of different kinds of ILCOFs materials, including ILCOFs with IL moieties located on the main linkers, on the nodes, and on the side chains. We then discuss the ILCOFs for CO2 capture and conversion, including the reduction and cycloaddition of CO2. Finally, future directions and prospects for ILCOFs are outlined. This review is beneficial for academic researchers in obtaining an overall understanding of ILCOFs and their application of CO2 conversion. This work will open a door to develop novel ILCOFs materials for the capture, separation, and utilization of other typical acid, basic, or neutral gases such as SO2, H2S, NOx, NH3, and so on

    Organocatalytic Synthesis of α-Aminonitriles: A Review

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    α-Aminonitriles, which have anticancer, antibacterial, antiviral, and antifungal properties, have played an important role in pharmacology. Furthermore, they can also be used to synthesize natural and unnatural amino acids. The main bottleneck in the commercialization of these products is their large-scale production with controlled chirality. A variety of methods have been used to synthesize α-aminonitriles. Among other reported methods for preparing α-aminonitriles, the Strecker reaction is considered appropriate. Recent developments, however, have enabled the α-cyanation of tertiary and secondary amines by functionalizing the carbon–hydrogen (C–H) bond as an attractive alternative procedure for the preparation of α-aminonitriles in the presence of an oxidant and a cyanide source. In most cases, these reactions are catalyzed by transition metal catalysts, such as Fe, Cu, Rh, V, Au, Ru, Mo, Pt, Re, and Co, or by photocatalysts. As an alternative, organocatalysts can also be used to produce aminonitriles. Although there have been numerous reviews on the preparation of α-aminonitriles, no such reviews have been published specifically on the organocatalyzed synthesis of α-aminonitriles. Organocatalysis plays a significant role in synthesizing α-aminonitriles via Strecker-type reactions and cross dehydrogenative coupling reactions (CDC). In this mini review, we discuss the organocatalyzed synthesis of these molecules. A review of new organocatalysts for the synthesis of aminonitriles is expected to provide insight into the development of new industrial catalysts

    Economical synthesis strategy of RHO zeolites with fine-tuned composition and porosity for enhanced trace CO2 capture

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    Delicate modification of the silica contents and porous structures within RHO zeolites has been readily realized by adopting a variety of alkali metal-crown ether (AMCE) complexes as the templates. Compared to the previous protocols, up to 70% of the Cs+ cations could be substituted by much cheaper K+ cations and thus the synthesis costs of RHO zeolites could be impressively reduced. The subsequent Cs-133 and Na-23 MAS NMR spectra further reveal that the Cs+ cations may aggregate with crown ether in a form of monomer or dimer complex, which then plays a significant role in the structural direction of RHO zeolites, whereas the hydrated Na+ cations mainly serve as the charge balancing cations. Meanwhile, the addition of different amount of K+ cation could result in varying degrees of template-framework interaction and consequently generates RHO zeolites with diverse compositions. Finally, the proton-type RHO zeolites were applied to the adsorptive separation of CO2/CH4/N-2 mixture. Therein, the medium-silica ones achieve fine trade-off for the adsorption capacity, selectivity and heat even under ultralow CO2 concentration, which makes them potential candidates for trace CO2 capture

    Organocatalytic Synthesis of α-Aminonitriles: A Review

    No full text
    α-Aminonitriles, which have anticancer, antibacterial, antiviral, and antifungal properties, have played an important role in pharmacology. Furthermore, they can also be used to synthesize natural and unnatural amino acids. The main bottleneck in the commercialization of these products is their large-scale production with controlled chirality. A variety of methods have been used to synthesize α-aminonitriles. Among other reported methods for preparing α-aminonitriles, the Strecker reaction is considered appropriate. Recent developments, however, have enabled the α-cyanation of tertiary and secondary amines by functionalizing the carbon–hydrogen (C–H) bond as an attractive alternative procedure for the preparation of α-aminonitriles in the presence of an oxidant and a cyanide source. In most cases, these reactions are catalyzed by transition metal catalysts, such as Fe, Cu, Rh, V, Au, Ru, Mo, Pt, Re, and Co, or by photocatalysts. As an alternative, organocatalysts can also be used to produce aminonitriles. Although there have been numerous reviews on the preparation of α-aminonitriles, no such reviews have been published specifically on the organocatalyzed synthesis of α-aminonitriles. Organocatalysis plays a significant role in synthesizing α-aminonitriles via Strecker-type reactions and cross dehydrogenative coupling reactions (CDC). In this mini review, we discuss the organocatalyzed synthesis of these molecules. A review of new organocatalysts for the synthesis of aminonitriles is expected to provide insight into the development of new industrial catalysts

    Organic-Free, ZnO-Assisted Synthesis of Zeolite FAU with Tunable SiO2/Al2O3 Molar Ratio

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    Zeolite FAU with tunable SiO2/Al2O3 molar ratio has been successfully synthesized in the absence of organic structure-directing agents (OSDA). Specifically, the addition of zinc species contributes to the feasible and effective adjustment of the framework SiO2/Al2O3 molar ratio between about 4 and 6 depending on the amount of zinc species added in the batch composition. In contrast, a typical OSDA such as tetramethylammonium hydroxide (TMAOH) has a limited effect on the SiO2/Al2O3 molar ratio of the zeolite. The role of zinc species is essential for the crystallization of zeolite FAU with a higher SiO2/Al2O3 molar ratio under the particular synthesis conditions. It is speculated that zinc species may suppress the incorporation of aluminum into the aluminosilicate framework, which is due to the Coulombic repulsive interaction. A higher SiO2/Al2O3 molar ratio is also found to be accompanied by a lower CO2 adsorption heat for CO2/CH4 separation

    Targeted Synthesis of Ultrastable High-Silica RHO Zeolite Through Alkali Metal-Crown Ether Interaction

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    High-silica RHO zeolite was directly synthesized using an alkali metal-crown ether (AMCE) complex as organic structure-directing agent (OSDA). Derived from the UV-vis spectra and zeolite patterns, the crown ethercesium cation interaction was found to have crucial effect on the enhancement of silica content within the zeolite framework. The synthesized RHO zeolites possess up to four times larger silica/alumina ratio (SAR) values than that in their conventional form, which gives them extraordinarily rigid frameworks even after hydrothermal aging under 800 degrees C. Compared to commercial zeolites, copperexchanged high-silica RHO zeolites demonstrate considerably high reaction activity in NOX removal, making them promising candidates for diesel exhaust treatment

    Cost-effective synthesis of CHA zeolites with controllable morphology and size

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    Cost-effectively develop zeolites with controllable morphology and size is significant in design and optimization of the physical properties for CO2 /CH4 adsorption separation. Herein, we report the synthesis of CHA zeolites with tunable morphology and size by a facile one-step dual template-directed strategy. A mixture of organic structure-directing agents (OSDA) composed of N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) and tetramethylammonium hydroxide (TMAOH) was employed and found to function cooperatively in directing the crystallization of CHA zeolites. Additionally, the dual template strategy reduced the consumption of expensive TMAdaOH to a great extent. The crystal morphology and size were remarkably dependent on TMAOH concentration in the dual template-directed synthesis system, regardless of TMAdaOH concentration. We demonstrate that the gradual decrease of TMAOH concentration in the batch composition enables a fine-tuning of the zeolite morphology from cubic to rough sphere crystals, accompanied by the size ranging from ca. 3 mu m to 400 nm. We speculate that the two organic species work synergistically in the formation of CHA crystals, where TMAdaOH is the microporous structure director, and TMAOH plays a role in bridging neighboring particles via electrostatic interactions. The variation of crystal size is confirmed to have considerable influence on CO2/CH4 separation performances. Moreover, the ability to tailor the physical properties of CHA zeolite by dual template method makes it possible to optimize the performances in other commercial applications
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