Facile Synthesis,Characterization, and Catalytic Behavior of a Large‐Pore Zeolite with the IWV Framework

Large‐pore microporous materials are of great interest to process bulky hydrocarbon and biomass‐derived molecules. ITQ‐27 (IWV) has a two‐dimensional pore system bounded by 12‐membered rings (MRs) that lead to internal cross‐sections containing 14 MRs. Investigations into the catalytic behavior of aluminosilicate (zeolite) materials with this framework structure have been limited until now due to barriers in synthesis. The facile synthesis of aluminosilicate IWV in both hydroxide and fluoride media is reported herein using simple, diquaternary organic structure‐directing agents (OSDAs) that are based on tetramethylimidazole. In hydroxide media, a zeolite product with Si/Al=14.8–23.2 is obtained, while in fluoride media an aluminosilicate product with Si/Al up to 82 is synthesized. The material produced in hydroxide media is tested for the hydroisomerization of n‐hexane, and results from this test reaction suggest that the effective pore size of zeolites with the IWV framework structure is similar to but slightly larger than that of ZSM‐12 (MTW), in fairly good agreement with crystallographic data.     

Toward Efficient Synthesis of Chiral Zeolites: A Rational Strategy for Fluoride-Free Synthesis of STW-Type Zeolite

The STW-type zeolite is attractive for developing novel enantioselective syntheses/separation of chiral compounds because it is the only chiral zeolitic microporous material whose enantioenriched synthesis has been achieved. In addition to the conventional industries in which zeolites are used, STW should have diverse industrial applications in the pharmaceutical and food industries. However, the toxic and caustic fluoride required for synthesizing STW severely hinders its commercialization by mass production. Herein, we report the first example of fluoride-free STW synthesis, in which the two roles of fluoride—formation of a zeolitic framework rich in tetravalent T-atoms and promotion of double 4-membered ring unit formation—were substituted by dry gel conversion and Ge addition, respectively. The STW obtained was highly crystalline, with a similar micropore volume and thermal stability as those of original fluoride-based STW. Our approach is promising not only for the fluoride-free synthesis of enantiomeric STW but also for general fluoride-free syntheses.     

Seed‐Assisted,One‐Pot Synthesis of Hollow Zeolite Beta without Using Organic Structure‐Directing Agents

Hollow aluminosilicate zeolite beta was successfully synthesized by adding CIT‐6, that is, zincosilicate zeolite, which has the same topology as beta, as seeds to the Na‐aluminosilicate gel without the need for organic structure‐directing agents. One important factor in the successful organic structure‐directing agent (OSDA)‐free synthesis of hollow beta crystals is the solubility of the seed crystals in alkaline media. CIT‐6 was less stable than aluminosilicate zeolite beta in alkaline media and the solubility changed depending on whether the crystals were calcined or not. The hollow beta could be obtained by using the uncalcined CIT‐6 seed crystals. The volumes of intra‐crystalline voids were tuned by changing the reaction time and the initial gel compositions, such as the SiO₂/Al₂O₃ and Na₂O/SiO₂ ratios. We estimated that the intra‐crystalline voids were formed through the dissolution of the seed crystals, just after the crystal growth of new beta on the outer surface of the seeds. In addition, new crystal growth toward inside of the void was also observed by TEM. On the basis of the characterization data, such as chemical analysis, N₂‐adsorption/desorption measurements, and TEM observation, a formation mechanism of the intra‐crystalline voids is proposed and discussed.     

Efficient Synthesis of Dimethyl Ether from Methanol in a Bifunctional Zeolite Membrane Reactor

A sandwich FAU–LTA zeolite dual‐layer membrane has been developed and used as a catalytic membrane reactor for the synthesis of dimethyl ether (DME). In the top H‐FAU layer with mild acidity, methanol is dehydrated to DME. The other reaction product, water, is removed in situ through a hydrophilic Na‐LTA layer, which is located between the porous alumina support and the H‐FAU top layer. The combination of mild acidity with the continuous removal of water results in high methanol conversion (90.9 % at 310 °C) and essentially 100 % DME selectivity. Furthermore, owing to the selective and continuous removal of water through the Na‐LTA membrane, catalyst deactivation can be effectively suppressed.     

稻壳基高纯度NaP1沸石的制备及其庚烷异构性能评价

以稻壳为硅源采用煅烧-水热法合成NaP1沸石,考察了不同硅铝比(nSiO2/nAl2O3)、水钠比(nH2O/nNa2O)、晶化温度、晶化时间对沸石结晶度的影响,并以其为载体制备x％Ni/NaP1(x％为Ni与NaP1的质量比)型烷烃异构催化剂.采用X射线衍射、红外光谱、扫描电子显微镜、透射电子显微镜-X射线能谱、N2...     

Dual‐Mesoporous ZSM‐5 Zeolite with Highly b‐Axis‐Oriented Large Mesopore Channels for the Production of Benzoin Ethyl Ether

Dual‐mesoporous ZSM‐5 zeolite with highly b axis oriented large mesopores was synthesized by using nonionic copolymer F127 and cationic surfactant CTAB as co‐templates. The product contains two types of mesopores—smaller wormlike ones of 3.3 nm in size and highly oriented larger ones of 30–50 nm in diameter along the b axis—and both of them interpenetrate throughout the zeolite crystals and interconnect with zeolite microporosity. The dual‐mesoporous zeolite exhibits excellent catalytic performance in the condensation of benzaldehyde with ethanol and greater than 99 % selectivity for benzoin ethyl ether at room temperature, which can be ascribed to the zeolite lattice structure offering catalytically active sites and the hierarchical and oriented mesoporous structure providing fast access of reactants to these sites in the catalytic reaction. The excellent recyclability and high catalytic stability of the catalyst suggest prospective applications of such unique mesoporous zeolites in the chemical industry.     

Rapid Synthesis of an Aluminum‐Rich MSE‐Type Zeolite by the Hydrothermal Conversion of an FAU‐Type Zeolite

An aluminum‐rich MSE‐type zeolite (Si/Al is as small as 7) has been successfully synthesized in a remarkably short crystallization period of only 3 days by the hydrothermal conversion of an FAU‐type zeolite, presumably by the assembly of four‐membered‐ring (4‐R) aluminosilicate oligomers supplied by the double 6‐R (D6R) components of the FAU framework with the aid of the structure‐directing agents and seed crystals. The dealuminated version of the aluminum‐rich MSE‐type zeolite showed a high level of coke durability in addition to a significant yield of propylene, which indicates that this novel zeolitic material is suitable for industrial applications as a highly selective and long‐lived catalyst.     

双杂原子Ti-Mn-β沸石的合成、表征及催化苯酚羟化反应

采用水热合成法在SiO2-TiO2-MnO2-(TEA)2O-H2O-NH4F体系中合成了Ti-Mn-β沸石。 运用X射线衍射、红外光谱、固体紫外可见漫反射、热重-差热、扫描电子显微镜和X射线光电子能谱等技术手段对样品进行了表征,探讨了影响Ti-Mn-β沸石合成的因素。 Ti-Mn-β沸石在以H2O2为氧化剂的苯酚羟基化反应中表现出较好的催化活性,苯酚的转化率为29.8％,邻苯二酚和对苯二酚的选择性分别为70.9％和26％。     

An Interrupted Zeolite PKU-26 and Its Transformation to a Fully Four-Connected Zeolite PKU-27 upon Calcination

The thermal stability and structural transformation mechanism are critical for the industrial applications of zeolites and the design of new framework types. Herein, a new zeolite PKU-26 has been hydrothermally synthesized under fluoride conditions using a tetraethylammonium (TEA⁺) cation as the structure-directing agent (SDA) and its framework contains partial Q³ T atoms [Q³ for T(−O−T)₃OH]. Upon calcination, PKU-26 processed a single-crystal to single-crystal transformation to another novel zeolite PKU-27 with the elimination of terminal −OH groups and enhanced thermal stability up to 650 °C, exhibiting the first Q³→Q⁴ transformation [Q⁴ for T(−O−T)₄] in 3D zeolite frameworks. The mechanism of the structural transformation, involving proton transfer, framework dehydration, and TO₄ reconstruction, is proposed and supported by theoretical calculations.     

Hydrothermal Synthesis of Pencil‐like SAPO‐5 and Observation of Its Reversed Crystal‐Growth Process

SAPO‐5 with a novel hexagonal pencil‐like morphology was hydrothermally synthesized from hydrogels that contain triethylamine and high concentrations of acetic acid at 180 °C for 48 h. The effect of the acetic acid concentration was examined and indicated that usage of a high concentration of acetic acid is crucial to the synthesis of SAPO‐5 with a pencil‐like morphology. The time‐dependent growth process of novel SAPO‐5 was observed by scanning electron microscopy with the aid of acid treatment to remove the amorphous materials for clearer observation. The samples were also characterized by X‐ray diffraction and Fourier‐transform infrared spectroscopy. The results show that the crystal growth at the early stage follows the reversed crystal‐growth route. First, the crystallization occurs on the surface of the aggregated amorphous ellipsoidal particles to form a hexagonal prism crystal shell with the encapsulation of amorphous materials. Then, the amorphous materials wrapped inside start to grow to a hexagonal prism inside the hollow larger hexagonal prism shell. Finally, the interior hexagonal prism continues to grow to the two ends with its length beyond that of the larger one by means of the Ostwald ripening process, thus forming the pencil‐like crystal.     

合成TS-1分子筛的结晶动力学及催化性能研究

 以自制的四丙基氢氧化铵为模板剂，通过改进经典的水热晶化操作步骤，快速合成出TS－1分子筛，并对其合成过程进行了结晶动力学研究．结果表明，在所考察的晶化温度下，TS－1的成核诱导期均很短，且晶体的成核及生长速率随晶化温度的升高而增大；其表观成核活化能和表观生长活化能分别为33．60和36．73kJ／mol，比经典的水热合成体系所得数值略小．晶化温度越高，晶化液的pH值变化越显著；分子筛结构的迅速形成与晶化液pH值的快速上升过程相一致．高温下合成的TS－1分子筛对苯酚羟基化反应的催化活性更高．导致TS－1分子筛催化活性差异的主要原因是进入分子筛骨架中钛的含量不同，以及样品的结晶度不同．在不同晶化温度下所合成的TS－1分子筛颗粒尺寸稍有差别，但均为100nm左右．     

From Molecular Fragments to Crystals: A UV Raman Spectroscopic Study on the Mechanism of Fe‐ZSM‐5 Synthesis

The nucleation process of iron‐exchanged zeolite Fe‐ZSM‐5, from the assembly of distorted tetrahedrally coordinated iron species and silicate rings in the precursor to the final Fe‐ZSM‐5 crystals, as well as variations in the coordination environment of iron, were studied by UV resonance Raman spectroscopy and complementary techniques.

     

Microporous Polymers from a Carbazole‐Based Triptycene Monomer: Synthesis and Their Applications for Gas Uptake

Two kinds of novel organic microporous polymers TCP s ( TCP‐A and TCP‐B ) were prepared by two cost‐effective synthetic strategies from the monomer of tricarbazolyltriptycene ( TCT ). Their structure and properties were characterized by FT‐IR, solid ¹³C NMR, powder XRD, SEM, TEM, and gas absorption measurements. TCP‐B displayed a high surface area (1469 m² g^?1) and excellent H₂ storage (1.70 wt % at 1 bar/77 K) and CO₂ uptake abilities (16.1 wt % at 1 bar/273 K), which makes it a promising material for potential application in gas storage.