Synthesis of Zeolite L. Tuning Size and Morphology

Summary. A convenient synthesis of zeolite L is presented. The size of the crystals can be tuned between 30 and 6000nm, spanning a volume range of seven orders of magnitude. The zeolite L crystals, which typically feature a cylindrical morphology, are synthesized with various aspect ratios ranging from elongated to disc-shaped. The importance of obtaining zeolite crystals with well-defined size and morphology is discussed in view of potential applications of zeolite L containing organic dye molecules as guests.This revised version was published online in February 2005. In the previous version the issue was not marked as a special issue, and the issue title and the editor was missing     

Effect of aging temperature of alkaline aluminosilicate and silicate gels on the kinetics of crystallization of zeolite ZSM-5 and silicalite-1

The temperature dependences of nucleation of zeolite ZSM-5 and silicalite-I pass through extrema in the range from 110 °C to 120 °C. Despite having the same crystalline structures, zeolite ZSM-5 has a maximum and silicalite-1 has a minimum of nucleation in the temperature range mentioned. A method for preparation of single crystals of silicalite-1 up to 150 m in size has been developed. The comparison of the curves of the temperature dependences of nucleation for zeolites Na-X, Na-A, and ZSM-5 shows that the positions of the maxima on these curves are determined by the type of the crystal structure of zeolite.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1091–1095, May, 1996.     

Encapsulation of Metalloporphyrins in Nanometer-sized Zeolites:Synthesis,Characterization and Catalysis

The lasting extensive interest in zeolite molecular sieves, a class of nanoporous aluminosilicate oxidic crystals, lies in their three special properties:(a) the nanoscale porous cage that can serve as size- and/or shape-based host to recognize, select, and discriminate among the molecules, (b) the well-defined and controllable charge environment and charge strength inside pores that can facilitate or inhibit certain chemical processes, and (c) the well-organized pores/channels that can host the organization and assembly of molecules to display novel optical or electrochemical properties. Zeolitic materials possess yet another very important property, namely, their huge surface-to-volume ratio. Conventionally synthesized zeolites are quite large crystals with grain size at micrometer scale. This implies that the dominant portion of the "overall surface area" is attributable to the " interior surface" of nanopores/nanochannels instead of the "exterior surfaces" of the crystal powders. In many situations, this has limited the efficacy of zeolite materials, particularly in many catalysis-related applications. In order to improve the efficiency of catalysis of zeolite materials, it is often desirable to achieve a balanced ratio (~1) between interior-surface-area and exterior-surface-area, namely, to significantly reduce the size of zeolite crystals.     

Facile synthesis of 5A zeolite from attapulgite clay for adsorption of <Emphasis Type="Italic">n</Emphasis>-paraffins

5A zeolites were facilely synthesized from attapulgite clay and sodium aluminate precursors. The optimum synthesis condition for 4A zeolite (Na-form) were H₂O/attapulgite ratio of 40:1 volume/mass, NaOH/attapulgite mass ratio of 2.35:1, the crystallization time was 4 h at 80–85 °C. The 4A zeolite was converted to related 5A zeolite (Ca-form) through ionic exchanges using calcium chloride solution with the Si/Al mole ratio of 1.3. SEM images demonstrated that as-synthesized 5A zeolites are ordered cubic crystals, average crystals length dimension is 1–2 μm. And the zeolites product had a specific surface area of 482 m² g^?1 and total pore volume of 0.274 cm³ g^?1. The static adsorption experiments showed that the equilibrium adsorption capacities of n-decane and n-pentadecane on produced 5A zeolite were 0.253 and 0.510 g g^?1, respectively. And the adsorption equilibrium time of n-decane and n-pentadecane on 5A zeolite were 45 and 60 min, respectively. The experimental adsorption data of n-decane and n-pentadecane on three zeolites could be properly fitted by the Langmuir–Freundlich isotherm model.     

High Selective Alkylation of Aniline with Methanol to N-Methylaniline over [Fe]-KL Molecular Sieves

In the alkylation of aniline with methanol, [Al]-KL zeolite exhibits a much higher NMA (N-methylaniline) selectivity (>95%) and more stable activity with time on stream than NaX, NaY and Na under the same experimental conditions. Incorporation of an appropriate amount of Fe into the framework of zeolite L can enhance the reaction activity without loss of high NMA selectivity. This improvement is attributed to an increase in the basicity of the zeolite as shown by pyrrole-IR spectra. The high NMA selectivity of zeolite L may be due to its one-dimensional channel structure with no large cavities and its lower number of accessible acid sites.     

A facile method to tune zeolite L crystals with low aspect ratio

We demonstrate an alternative route to tune the morphology of zeolite L crystals using C(2)H(5)OH as the co-solvent in the synthesis gel. A low aspect ratio (0.2 to 0.4) of zeolite L crystals was obtained at lower synthesis temperature (150 °C) and shorter synthesis duration (3 days).     

Cover Picture: Microcontainers with Fluorescent Anisotropic Zeolite L Cores and Isotropic Silica Shells (Angew. Chem. Int. Ed. 7/2009)

Nanocontainers composed of zeolite L crystals were filled with fluorescent dyes and used as the core of a silica “box‐in‐a‐box” construction as in Russian matryoshka dolls, as described by A. Guerrero‐Martínez, L. de Cola, and co‐workers in their Communication on page 1266 ff. The anisotropic cores and isotropic shells of the multicolor emitting systems are separated by a polyelectrolyte layer and can be addressed independently. This approach opens fascinating routes for the construction of multifunctional nanosystems.

     

Effect of Sodium Concentration on the Synthesis of Faujasite by Two-step Synthesis Procedure

The relationship between the concentration of sodium cations and the properties of faujasite(FAU) zeolite was investigated using a two-step synthesis procedure including (1) formation of amorphous aluminosilicate precursors and separation of amorphous nanoparticles, and (2) transformation of these amorphous particles into zeolite crystals by treatment with alkali solutions(NaOH). Three representative samples including two nano-sized zeolites and one micron-sized zeolite were prepared using different concentrations of sodium hydroxide. The crystallization process of these zeolites was studied in detail by Fourier transform infrared(FTIR) spectrometry, nuclear magnetic resonance spectroscopy(NMR), X-ray diffraction(XRD), scanning electron microscopy (SEM), transmission electron microscopy(TEM), and N₂ adsorption. The results indicated that minor changes in the concertation of inorganic cations can significantly shorten the induction period and crystallization time and thus affect the morphology, size and chemical composition of the zeolite crystals.     

AFM and XRD investigation of crystalline vapor-deposited C60 films

The morphological and structural properties of C₆₀ films deposited on quartz substrates by sublimation at 320–500° C under high vacuum have been investigated using atomic force microscopy (AFM) and reflection X-ray diffraction (RXRD). The thickness of the films varied between 0.2 m and 10 m. AFM showed that the films consist predominantly of cubic crystals of a few micrometer in size with well-developed (111) and (100) faces. The crystallographic investigation revealed a strongly preferred [111] growth direction which is very sensitive to the deposition rate and substrate temperature. The influence of the experimental parameters on the morphology of the crystals and on the preferred orientation of the films is discussed in view of the AFM and RXRD results.     

Preparation of a Completely Oriented Molecular Sieve Membrane

Growth of oriented seed crystals on a substrate led to a completely oriented and continuous membrane of LTA-type zeolite. The seed crystals of cubic morphology were dip-coated onto a tilted substrate (see schematic diagram) with the zeolite channels normal to the surface. The substrate was hydrothermally treated in a reaction mixture containing the organic ligand 2,2-bis(hydroxymethyl)-2,2',2"-nitrilotriethanol, which lowers the degree of supersaturation of [Al(OH)(4)](-) ions and preferentially facilitates the intergrowth of the seed crystals.     

Uranium sorption from aqueous solutions on sodium-form of HEU-type zeolite crystals

The uranium sorption from aqueous solutions (concentration range 50–20.000 mg/l) by the sodium-form (Na-form) of HEU-type zeolite crystals (particle-size <20 m) has been investigated by means of a batch-type method. The INAA, RI-XRF, powder-XRF, SEM-EDS and FT-IR techniques were used for the study of the experimental products. The absolute uranium uptake by the material reached the value of 11.68 mg/g in the case of initial concentraton 20,000 mg/l. On the other hand theK _d -values indicated that the relative uranium uptake, and consequently the percentage of removal, is higher for concentrations below 100 mg/l. The uranium uptake by the zeolite is attributed to different sorption processes such as ion-exchange, adsorption and surface precipitation, taking place both to the interior and the surface of the crystals and strongly depending on the pH of the solutions. The investigated zeolitic material was sufficiently resistant at the low initial pH of the solutions with dealumination phaenomena only observed in the case of the most acidic solution used.     

HCl处理后局部有序Y沸石的二次晶化

将商品 Y 型沸石用 HCl 处理后, 运用 X 射线粉末衍射, 透射电镜和扫描电镜、红外光谱及 27Al 和 29Si 魔角旋转核磁共振对其进行了表征. 结果表明, 酸处理后 Y 沸石接近无定形, 其长程有序性遭到破坏, 但还保留部分局部结构. 以不同浓度酸处理后的 Y 沸石为前驱体, 在 150 oC, 0.3 mol/L NaOH 条件下采用蒸汽辅助干胶转化法进行二次晶化, 可以获得丝光沸石, 其相纯度与前驱体的 Si/Al 密切相关. 随 Si/Al 比不同, 所得丝光沸石形貌由纳米针状堆积逐渐向微米单块状变化, 且其比表面积可达 400 m2/g 以上, 微孔孔容在 0.19 cm3/g.     

一种新型共生沸石(T-L)的合成与表征

在Na₂O-K₂O-Al₂O₃-SiO₂-H₂O体系中水热合成了一种新型的共生沸石, 它由L型沸石生长在T型沸石的一端而形成, 称之为T-L型沸石. 通过XRD, SEM, TEM, EDX, IR等手段对其进行了初步的表征. SEM相片表明这种沸石具有特殊的铆钉状外形; 在TEM相片上可以清楚地看到L型沸石的大孔道, 此孔道与L型沸石的表面垂直. 通过EDX的数据计算发现共生沸石的两相有不同的骨架硅铝比: T型沸石部分Si/Al＝3.71, L型沸石部分Si/Al＝3.41. 在该样品中B酸大于L酸.     

键阻断原理构建中孔A型沸石

采用不同类型的有机硅烷化SiO₂作为基本合成单元, 制备了具有晶内中孔的A型沸石。考察了反应碱度、Si/Al比、晶化时间等合成条件对产品的影响。结果表明, 甲氨基丙基三甲氧基硅烷是合成中孔A型沸石的最佳硅烷化试剂;硅烷化试剂的应用, 使中孔沸石晶化过程可以通过“键阻断原理”有效控制;沸石的中孔尺寸可以通过不同类型的有机硅烷化试剂进行调控; 一定范围内, 其外比表面积、中孔体积随SiO₂表面硅烷化度的增加而增加。通过沸石晶化过程中的“键阻断”, 可以制备具有晶内中孔的A型沸石。     

键阻断原理构建中孔A型沸石

采用不同类型的有机硅烷化SiO2作为基本合成单元,制备了具有晶内中孔的A型沸石。考察了反应碱度、Si/Al比、晶化时间等合成条件对产品的影响。结果表明,苯胺基丙基三甲氧基硅烷是合成中孔A型沸石的最佳硅烷化试剂;硅烷化试剂的应用,使中孔沸石晶化过程可以通过"键阻断原理"有效控制;沸石的中孔尺寸可以通过不同类型的有机硅烷化试剂进行调控;一定范围内,其外比表面积、中孔体积随SiO2表面硅烷化度的增加而增加。通过沸石晶化过程中的"键阻断",可以制备具有晶内中孔的A型沸石。     

Proton activity inside the channels of zeolite L

The proton activity inside the channels of zeolite L has been studied by investigating dye-loaded zeolite L crystals under different conditions, such as water content, nature of the counterions, and nature of the solvent. The discussion is made within the frame of three types of dye-loaded zeolite L systems, classified according to their ability to exchange matter (dyes, cations, solvent, and other small molecules) with the environment. The classification refers to dye-loaded zeolites. The term "closed" and "semi-open" characterize different possibilities of the channels to exchange small molecules, cations, and solvent molecules with the environment, but not dyes. The "open" systems also allow for dye exchange. UV-visible and fluorescence spectroscopy have been used to observe the proton activity inside the zeolite L channels. The influence of the proton activity on the luminescence of encapsulated dyes is discussed, special attention being given to luminescence quenching by excited-state protonation. Partially proton-exchanged zeolite L can be a superacid, whereas for the M-exchanged form (M: K(+), Li(+), Cs(+), Mg(2+), Ca(2+)) the pH ranges from about 2.5 to 3.5. For these last forms, the differences in pH are due to the acid-base reactions of the respective metal cations with water inside the zeolite. Finally, we describe an easy experimental procedure that can be used to tune the proton activity inside the zeolite L to a considerable extent.     

Transmission electron microscope observations of fibrillar-to-lamellar transformations in melt-drawn polymers — I. Isotactic polypropylene

The transformation during heat treatment from a fibrillar to a lamellar morphology in highly oriented polypropylene is followed by transmission electron microscopy (TEM) and small angle electron scattering (SAES). While the as drawn films exhibit long (up to 1m) continuous fibrillar crystals, those crystals disintegrate into short crystalline blocks which finally aggregate into a lamellar morphology during the heat treatment. After even longer heat treatment the lamellar crystals start to thicken.Work supported by the Alexander von Humboldt Stiftung and Deutsche ForschungsgemeinschaftOn leave from Department of Chemical Engineering University of Delaware, Newark, DE 19711, USA     

高性能AlPO4-14分子筛膜的制备及气体分离性能

制备了高性能的AlPO₄-14分子筛膜. 首先通过控制反应溶胶中水和模板剂的含量制备了形貌均一的AlPO₄-14分子筛, 分子筛的尺寸为15~18 mm; 然后采用晶种法即在反应凝胶中加入分子筛作为晶种进一步调控分子筛的大小, 使得AlPO₄-14分子筛的尺寸从15~18 mm减小到2~3 mm, 得到形貌均一的纯相片状晶体, 同时有效缩短了制备时间; 最后以多孔管状莫来石为支撑体, 采用二次生长法制备AlPO₄-14分子筛膜. 考察了2种不同大小的晶种对膜形貌和性能的影响, 发现以大尺寸的分子筛(15~18 mm)作为晶种制备的分子筛膜的分离层存在较多缺陷, 而采用小尺寸的晶种(2~3 mm)制备的膜层较均一致密. AlPO₄-14分子筛膜经高温脱除模板剂后仍然保持着纯相的AlPO₄-14晶型, 表明二次生长法促进了AlPO₄-14晶体在膜层中的生长且使其具有更高的结晶度和热稳定性. 在25 ℃, 100 kPa下, AlPO₄-14分子筛膜对H₂/CH₄, CO₂/CH₄和H₂/CF₄的理想分离因子分别为28, 40和1047, 且H₂和CO₂的渗透速率分别为6.3×10 ^-7和9×10 ^-7 mol·(m ²·s·Pa) ^-1; 对等摩尔CO₂/CH₄混合气体的分离因子为81.5, 且CO₂的渗透速率为8.8×10 ^-7 mol·(m ²·s·Pa) ^-1.     

Tailoring the Structure of Hierarchically Porous Zeolite Beta through Modified Orientated Attachment Growth in a Dry Gel System

The crystallization of zeolite beta in a dry gel system is found to follow the orientated attachment growth route, escorted with a temporal morphology change from bulky gel, through aggregation of the particulate to large zeolitic crystals. Modification of the precrystallized gel with organosilanes can be used to tune the morphology of the ultimate beta. When hexadecyltrimethoxysilane (HTS) is employed to modify precrystallized gel, a resumed secondary growth produces a hybrid mesocrystal of agglomerated nanozeolites. Combustive removal of organics leads to the formation of hierarchically porous zeolite beta of 100 to 160 nm, composed of nanocrystal building units ranging from 20 to 40 nm, with a noticeable micropore volume of 0.19 mL g^?1 and a meso/macropore size between 5 and 80 nm. Conversely, when 1,8‐bis(triethoxysilyl)octane (BTO) is utilized to modify the same precrystallized gel, assemblages of discrete beta nanozeolite of around 35 nm are generated. These assemblages construct a hierarchical zeolite beta with a micropore volume of 0.20 mL g^?1 and auxiliary pores ranging from 5 to 100 nm. Both organosilanes bring about well‐connected hierarchical pore networks. HTS has little effect on the Brønsted/Lewis acidity, whereas BTO causes a substantial reduction of strong Brønsted acid sites. The hierarchical beta zeolite‐supported Pt catalyst exhibits improved catalytic performance for the hydroisomerization of n‐heptane.     

Hydrogen peroxide biosensor based on direct electrochemistry of hemoglobin immobilized on gold nanoparticles in a hierarchically porous zeolite

Highly dispersed gold nanoparticles (AuNPs) were introduced into a hierarchically porous zeolite of the MFI type that contains mesopores and an inherently microporous structure. These represent a novel matrix for the immobilization of biomolecules. The composites were characterized by FTIR, X-ray diffraction, UV–vis spectroscopy, transmission electron microscopy, nitrogen sorption measurements, and electrochemical impedance spectroscopy. The crystallinity and morphology of the zeolite is not compromised by incorporating the AuNPs with their size of 3–20 nm. A sensor for hydrogen peroxide (H₂O₂) was fabricated by incorporating hemoglobin into the matrix and placing it on the surface of a glassy carbon electrode. The resulting biosensor exhibits excellent bioelectrocatalytic capability for the reduction of H₂O₂. The amperometric response at ?0.4 V linearly depends on H₂O₂ in the 1.0 μM to 18 mM concentration range. The detection limit is 0.8 μM (at an S/N of 3). Its good sensitivity, stability and reproducibility make the modified hierarchically porous zeolite a promising new matrix material for protein immobilization and the construction of biosensors.