The Link between ZSM-5 Zeolite Crystallization and Mesopore Formation by Leaching

Acid or base leaching are well-established tools in the synthesis of mesoporous zeolites. Previous studies suggest an inherent link between the structure-property relationship of mesoporous zeolites, that is, chemical resistance, pore diameter and distribution, with zeolite synthesis or crystallization conditions. The exact nature and/or origin of this link is currently however, poorly established. Here, we provide evidence how zeolite crystallization conditions influence the leaching behavior and thus structure of mesoporous zeolites. Electron microscopy and in situ small angle X-ray scattering both confirmed the crystallization of ZSM-5 to utilize both nanoparticles and oligomers as elemental building blocks. Utilization of these species is highly depended on supersaturation. The precursor solution of decreased water content favored a faster consumption of nanoparticles compared to its oligomers at the early stage of crystallization. Then the addition of oligomers can heal the surface imperfections and thus the resulting zeolite showed a higher resistance against acid leaching. In contrast, within the precursor solution of increased water content the slower consumption of nanoparticles led to crystals with a less robust rim. Defects existed in the rim due to limited healing by oligomers and, as such, mesopores can be created by the following post-treatment. Precise control over selected crystallization conditions can therefore further aid the design of optimized mesoporous zeolites.     

Hierarchical Zeolites-confined Metal Catalysts and Their Enhanced Catalytic Performances

The confinement of metal species within hierarchical zeolites combines the acidic/basic sites of zeolites, the enhanced mass transfer of mesoporous system, and the inside active metal sites, leading to high activity, unique selectivity, and superior stability in chemicals synthesis, energy and environment catalysis. To date, review on this emerging topic is rarely reported. Herein, we classify five metals-hierarchical zeolites composite (metal@hierarchical zeolites) according to the location of metals on hierarchical structure, including metals located on micropores, intercrystalline mesopores, intracrystalline mesopores, hollow nanobox and mesoporous shells. The synthesis and catalysis applications of metal@hierarchical zeolites composite are provided, highlighting the rational design of catalyst preparation, the improved catalytic efficiency and stability of metal species. Finally, we discuss the current limitations and future opportunities for this emerging field. This Review is expected to inspire more developments and applications of metal@hierarchical zeolites.     

介孔分子筛制备技术新进展—二次合成、超分子自组装和介孔生成剂法

具有内部介孔结构的多级孔分子筛兼具微孔分子筛和介孔材料的功能, 拥有良好的传质和催化特性. 在过去的几十年内, 介孔分子筛在催化、 吸附和分离领域发展迅速. 近年来, 新型合成方法的开发在很大程度上实现了介孔分子筛孔道结构、 组分及形貌灵活可控的调节. 本综述讨论了近期出现的多种新合成路径, 重点介绍了近期发展起来的二次合成制备低硅/铝介孔分子筛、 超分子自组装合成介孔分子筛及有机小分子原位合成介孔分子筛技术. 对这些合成技术的机理进行了讨论, 以期为介孔分子筛未来的发展提供思路. 文章的最后还讨论了不同的合成策略所面临的一些关键性挑战.     

微介孔复合分子筛合成及其在汽车冷启动尾气控制中的应用

分别采用稀溶液和浓溶液双模板剂两步水热合成法,以二氧化硅微硅粉和铝酸钠为硅源和铝源,第一步获得β分子筛晶种,第二步以β分子筛晶种为结构单元组装形成兼具MCM-41分子筛和β分子筛结构特点的复合型分子筛β/M(其中β是指β分子筛,M是指MCM-41介孔分子筛).采用X射线衍射(XRD)、傅里叶变换红外(FT-IR)光谱、氮气吸附(BET)和高分辨透射电镜(HRTEM)对样品的物相结构和微观形貌进行了表征,并对复合分子筛的合成过程进行了分析.结果表明:复合分子筛β/M的形成是微孔β结构和介孔MCM-41结构的竞争生长过程,β分子筛晶种的晶化时间和晶粒度大小对β/M复合分子筛的结构有重要影响.此外,我们以甲苯为探针分子,比较研究了三类分子筛β/M、MCM-41和β的原样以及经高温水热处理后样品的吸附性能,结果表明:β/M复合分子筛的热稳定性优于介孔分子筛MCM-41,其甲苯吸附容量比MCM-41和β分子筛的高,其中以浓溶液法合成的复合分子筛吸附容量最高.     

酸性条件下纯硅六方介孔分子筛的合成(Ⅱ)合成温度、时间的影响及其与碱性合成的比较

本文以十六烷基三甲基溴化铵为模板剂,正硅酸乙酯为硅源,考察了反应温度和时间对酸性条件下合成纯硅六方介孔分子筛的影响,并与碱性合成路径相比较。结果表明,由于无机物种与表面活性剂之间的相互作用不同,六方介孔分子筛的酸性合成经历了与碱性合成完全不同的机理。对要到性合成来说,由于六方结构的形成取决于稳定的模板胶束的存在,并不特别依赖于硅物种的缩合,故高温、长反应时间等有利于缩合的因素对提高产品质量几乎没有促进作用,较高的反应温度甚至起反作用。因此,酸性合成宜采用室温条件。     

Sustainable Synthesis of Hierarchically Porous Silicalite-1 Zeolite by Steam-assisted Crystallization of Solid Raw Materials Without Secondary Templates

Hierarchical silicalite-1 zeolites were obtained from the direct conversion of a mixture of ground solid raw materials via a steam-assisted crystallization(SAC) method without involvement of any mesoscale template. Only a trace amount of water was necessary during the crystallization, implying that the amount of water can be dramatically reduced, which still offers easy separation and high yields. The simple procedure involved only grinding and heating, which not only saves resources and energy, but also significantly reduces the discharge of eco-friendly synthesis of zeolites for practical applications. Compared to conventional bulk silicalite-1, the nanosized hierarchical zeolites with MFI structure show enhanced removal capabilities for methylene blue owing to their hierarchical porosity.     

气相转移法合成ZSM-5/SAPO-5复合分子筛

以磷酸、拟薄水铝石和硅溶胶为原料, 三乙胺为模板剂, 采用气相转移法合成了一系列ZSM-5/SAPO-5复合分子筛. 产物经X射线衍射、扫描电镜、X射线能量散射谱、红外光谱及N2 静态吸附法等手段对其进行了表征, 证明合成材料是以ZSM-5为核、SAPO-5为壳的双结构分子筛. 实验结果表明, 干胶制备条件及液相组成都影响复合分子筛的结晶. 晶化温度的提高和晶化时间的延长有利于分子筛结晶度的提高. VPT法可以减小SAPO-5和复合分子筛颗粒的直径, 改善SAPO-5在ZSM-5分子筛表面的分布. 重油裂化结果表明, 核壳结构复合分子筛对生成低碳烯烃的性能优于机械混合的样品.     

Direct synthesis of ordered mesoporous ZSM-5 zeolites from in situ crystallization of carbonaceous SBA-15

Two types of ordered mesoporous ZSM-5 zeolites with different mesopores were synthesized by a two-step method. First,carbonaceous SBA-15 was produced by in situ carbonization of SBA-15/P123 composite. Then the obtained SBA-15/C composite was transformed into crystallized mesoporous ZSM-5 by impregnation TPAOH followed by steam-assisted crystallization. The final calcined samples synthesized with typical SBA-15/P123 precursor showed a wormlike morphology with the mean mesopore size of 4.6 nm, while samples synthesized with the addition of trimethylbenzene as swelling agent in the precursor exhibited the morphology of microsphere with the mesopore size of about 9.5 nm. Both two types of mesoporous ZSM-5 zeolites exhibited large surface area and mesopore structure. The steam-assisted crystallization(SAC) was performed with lower consumption of solvents. This two-step method may also be suitable for synthesizing other ordered mesoporous zeolites used as catalysts in some catalytic processes.     

Broadening the Scope for Fluoride‐Free Synthesis of Siliceous Zeolites

Siliceous zeolites are ideally suited for emerging applications in gas separations, sensors, and the next generation of low‐k dielectric materials, but the use of fluoride in the synthesis significantly hinders their commercialization. Herein, we show that the dry gel conversion (DGC) technique can overcome this problem. Fluoride‐free synthesis of two siliceous zeolites—AMH‐4 (CHA‐type) and AMH‐5 (STT‐type), has been achieved for the first time using the method. Siliceous *BEA‐, MFI‐, and *MRE‐type zeolites have also been synthesized to obtain insights into the crystallization process. Charge‐balancing interactions between the inorganic cation, organic structure‐directing agent (OSDA), and Si?O^? defects are found to be an essential aspect. We quantify this factor in terms of the “OSDA charge/silica ratio” of the as‐made zeolites and demonstrate that the DGC technique is broadly applicable and opens up new avenues for fluoride‐free siliceous zeolite synthesis.     

Random‐Graft Polymer‐Directed Synthesis of Inorganic Mesostructures with Ultrathin Frameworks

A widely employed route for synthesizing mesostructured materials is the use of surfactant micelles or amphiphilic block copolymers as structure‐directing agents. A versatile synthesis method is described for mesostructured materials composed of ultrathin inorganic frameworks using amorphous linear‐chain polymers functionalized with a random distribution of side groups that can participate in inorganic crystallization. Tight binding of the side groups with inorganic species enforces strain in the polymer backbones, limiting the crystallization to the ultrathin micellar scale. This method is demonstrated for a variety of materials, such as hierarchically nanoporous zeolites, their aluminophosphate analogue, TiO₂ nanosheets of sub‐nanometer thickness, and mesoporous TiO₂, SnO₂, and ZrO₂. This polymer‐directed synthesis is expected to widen our accessibility to unexplored mesostructured materials in a simple and mass‐producible manner.     

Hydrothermally Stable and Catalytically Active Ordered Mesoporous Materials Assembled from Preformed Zeolite Nanoclusters

Microporous zeolites are widely used commercial catalysts, but their applications are intrinsically limited by their small channel diameters. Recent progress in solving this is used to ordered mesoporous materials such as MCM-41, HMS and SBA-15. These mesoporous materials have pore diameters of 30–60 Å and exhibit catalytic properties for the catalytic conversion of bulky reactants, but unfortunately, when compared with microporous zeolites, the catalytic activity and hydrothermal stability are relatively low, which severely hinders their practical applications. The relatively low catalytic activity and hydrothermal stability can be attributed to the amorphous nature of the mesoporous walls. We review here that the assembly of preformed zeolite precursors with surfactants can synthesize a series of ordered mesoporous materials, which include (1) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in alkaline media; (2) strongly acidic and hydrothermally stable mesoporous aluminosilicates synthesized in strongly acidic media; (3) hydrothermally stable mesoporous titanosilicates with catalytically active titanium species in oxidations; (4) hydrothermally stable mesoporous ferrisilicates. This work would open a door for the industrial application of mesoporous materials as catalysts for large molecules.     

沸石分子筛合成由微孔向中孔的飞跃

介绍了沸石分子筛合成由微孔向中孔的发展及中孔分子筛的合成近况, 比较了两类材料在合成、机理及模板作用的特殊性等方面的差异。     

Confined space synthesis. A novel route to nanosized zeolites

Confined space synthesis is a novel method in zeolite synthesis. It involves crystallization of the zeolite inside the pore system of an inert mesoporous matrix. In this way it is possible to prepare nanosized zeolites with a controlled size distribution by proper choice of the inert matrix. Here, confined space synthesis was adopted to prepare nanosized ZSM-5, zeolite Beta, zeolite X, and zeolite A with tailored crystal size distributions using mesoporous carbon blacks as inert matrices. All zeolites were characterized by X-ray powder diffraction, transmission electron microscopy, and nitrogen adsorption/desorption prior to and after removal of the carbon matrix. ZSM-5 with Si/Al ratios of 50, 100, and infinity (silicalite-1) were synthesized with controlled average crystal sizes in the range 20-75 nm. Nanosized zeolite Beta (7-30 nm), zeolite X (22-60 nm), and zeolite A (25-37 nm) were prepared similarly. Removal of the carbon matrix by controlled combustion allows a convenient method for isolation of the pure and highly crystalline zeolites. Therefore, confined space synthesis appears to be an attractive method for preparation of zeolites with a controlled size distribution.     

原位合成负载型MSU系列分子筛

采用原位合成法,使用壬基酚聚氧乙烯醚(Tx-15)和脂肪醇聚氧乙烯醚(AEO-19)做为模板剂,在中性条件下合成W.MSU-1和W-MSU-2介孔分子筛,合成中使用乙酰丙酮(HAcac)作为助剂,考察其对介孔结构的影响,通过X射线衍射仪(XRD)、傅里叶红外光谱仪(FT-IR)、扫描电镜(SEM)、低温N2吸附对样品进行表征.结果表明,加入过渡金属氧化物有助于介孔的形成,助剂的使用提高了孔的结构参数.     

NiY分子筛的合成及在微生物电解池阴极的析氢性能研究

在Na₂O-Al₂O₃-SiO₂-H₂O体系中添加硝酸镍,采用导向剂法合成了NiY分子筛。利用XRD、SEM、TEM、N₂吸附-脱附等手段对合成的NiY分子筛进行了表征。结果表明,随着镍添加量的增加,结晶度和zeta电位呈先增大后减小的趋势。当Si/Ni （mol ratio）大于5时,硝酸镍对分子筛的形成具有促进作用,当Si/Ni （mol ratio）小于5时,则具有抑制作用。晶粒粒径为1.5-3 μm,形貌为凹槽结构的六方或四方柱型,且具有微孔-介孔多级孔道结构特征。通过循环伏安曲线和极化曲线测试,在Si/Ni （mol ratio）=5时,样品的氧化还原性能最强,过电势最小,电催化活性最高。在12 h内,每4 mg的Si/Ni （mol ratio）=5样品,产气总量为10.1 mL,氢气纯度达81.69%,与Pt电极相比其氢气产量提高了28%。NiY分子筛表现出良好的析氢催化活性,有望取代Pt成为MEC新型阴极材料。     

RUB-13分子筛的合成及其甲醇制烯烃催化性能

采用水热法合成RUB-13分子筛，探讨了有机模板剂（OSDA）、硅源、晶化温度和水硅比等制备条件对RUB-13分子筛晶体结构的影响，考察了RUB-13分子筛在甲醇制烯烃（MTO）反应中的催化性能。结果表明，采用1，2，2，6，6-五甲基哌啶（PMP）为有机模板剂、白炭黑为硅源，在晶化温度为170℃的条件下，选择H₂O/Si比为100和80时可分别合成出高纯度的低硅铝比（Si/Al=100）和高硅铝比（Si/Al=200）的RUB-13分子筛晶体，且晶粒呈棒状形貌。H-Al-B-RUB-13（Si/Al=200）分子筛用于催化甲醇制烯烃反应时，在400℃下表现出高的低碳烯烃选择性（C_2-5⁼选择性达97.8%，丙烯选择性为54.5%），优于传统的H-SAPO-34和H-ZSM-5分子筛催化剂。     

有机官能团化介孔分子筛固载铑膦配合物的制备及其对己烯-1氢甲酰化的催化性能

 制备了表面有机官能团化的MCM-41和MCM-48介孔分子筛以及SiO2等载体固载铑膦配合物催化剂,考察了所制备催化剂对液相己烯-1氢甲酰化的催化性能,并用X射线衍射、BET、红外光谱和原子吸收光谱等技术对载体和催化剂的组成和结构进行了表征. 结果表明,固载化铑膦配合物对烯烃氢甲酰化的催化性能与有机官能团的种类及载体的结构有关; 固载于含胺基和腈基有机官能团化介孔分子筛载体的铑膦配合物表现出较高的催化活性和稳定性.     

高硅无铝Mo-Beta沸石的合成与结构表征

用水热晶化法合成了无铝Mo-Beta沸石,讨论了合成条件对无铝Mo-Beta沸石晶化的影响,通过化学分析、XRD、IR、DTA/TGA、TEM、NMR、ICP和UV-Vis紫外漫反射光谱测定了样品的n(SiO₂)/n(MoO₃)比,并对其结构进行了表征,结果表明,所合成的Mo-Beta沸石晶粒均匀,Mo存在于沸石骨架中,由于Mo的掺入,引起Beta沸石红外光谱、差热分析曲线及晶胞参数, ²⁹SiMASNMR谱等发生变化。     

EFFECTS OF SYNTHESIS PARAMETERS ON ZEOLITE ZSM-48 IN A SOLID REACTION MIXTURE SYSTEM

IntroduCtionReCently,zcoliteZSM-48hasbeenspehesizedinapurelysolidsystemll1.Thismethedusedtosynthesizezcolitescangndlyincreasetheyieldofpnductsperunitvolume,simplifythepr0cedresanddecreasethecnvironmentalpolluti0n.ThisincreasestheacualPOssibilityofsynthesisofhigh-silicazcolitesinchemicalindustry.MoreOver,itisalsohelpfulforstUdyingthezeolitecrystalliZai0nmechanism.ItiswellknownthatthesamewneofzeolitessynthesizedindifferentsystemshasdifferentcatalyticpropertiesduetothechangesoftheirfinestruC…     

碱土金属修饰NaY分子筛催化乳酸脱水制丙烯酸:碱性位对催化活性的影响

采用碱土金属(Mg,Ca,Sr,Ba)对NaY分子筛进行改性,并采用氮气物理吸附、X射线衍射、氨气及二氧化碳程序升温脱附等技术对样品进行了表征,考察了阳离子物种对NaY结构、表面酸碱分布等的影响,以进一步甄别影响催化剂活性的关键因素.结果表明,阳离子物种所引入的碱性位尤其是中强碱性位控制着丙烯酸的生成,而表面酸性位则影...