Synthesis of zeolite omega in an alcohol-water system

The crystallization of aluminosilicates at 130 ± 1°C from reaction mixtures containing varied amounts of alcohol (methanol, ethanol, butan-1-ol) and water has been studied. Zeolite species were identified by X-ray diffraction and electron microscopy. The type and morphology of the zeolite isolated were dependent upon the chain length and the alcohol:water ratio. The crystallization of zeolite omega was favored by the presence of longer-chain alcohols, ethanol, and butan-1-ol, and, also, a greater tolerance to alcohol with increasing chain length was observed. Zeolite omega produced in the mixed-solvent phase consisted of well-ordered “bundles” of long acicular crystals as compared to the spherulites formed in the aqueous system.     

The influence of fluoride on the crystallization kinetics of zeolite NaY

The crystallization time of zeolite NaY can be reduced by up to 80% in the presence of NaF. The optimal fluoride content and the minimal crystallization time can be calculated from the batch composition. Unlike hydroxide, the fluoride ion does not significantly decrease theSi/Al ratio of the framework. The rate constant of linear crystal growth can be expressed as a simple function of the equilibrium concentrations of the complexes Al(OH)₄⁻ and AlF(OH)₃⁻. The incorporation of monomeric aluminate species into the growing crystals seems to be the rate-determining step of zeolite NaY crystallization.     

Factors affecting the steam dealumination of zeolite omega

Three samples of zeolite omega with varying residual contents of sodium have been dealuminated by combined steam and acid treatments. The hydrolysis of the AlO bonds is a fast process that occurs mainly during the initial period of heating above 500° under steam. Sodium ions inhibit the reaction. The steamed solids contain mesopores ≅ 100 Å in diameter, but their porosity is not available to sorbents because of the presence of debris in which aluminum is in tetrahedral and octahedral configurations. Acid leaching removes all the nonframework tetrahedral aluminium and part of the octahedral one. This removal permits access to the microporous and mesoporous voids. Increasing the severity of the steam treatment increases the quantity of the disloged material that cannot be removed by the acid, but has little effect on the texture of the final solids. The TEM observations and the volumetric measurements suggest that the mesopores are not directly linked to the surface of the grains and are connected to each other by narrow necks.     

水凝胶相中载体预陈化法合成NaX型沸石膜

以相同的组成及晶化温度,首次采用载体预陈化法在α-Al_2O_3载体外表面成功合成NaX型沸石膜.水热处理前,载体在合成母液中经室温陈化,而后在363 K下进行水热处理.通过控制陈化时间,研究陈化对所合成沸石膜的影响.研究发现,陈化把沸石合成分为成核阶段及晶体生长阶段,并能够很好地控制沸石的成核和膜生长.陈化期间,非均相的水凝胶相中形成的沸石晶核沉积在载体表面,形成晶体生长的诱导层.较少的陈化时间会产生杂晶相,如方钠石(SOD)、菱沸石(CHA)、方沸石(ANA),这些杂晶相是沸石FAU的竞争相.随着陈化时间的增加,方解石(FAU)则变成了主要相,而为了获得纯的RAU沸石相,至少陈化一天.分别用XRD和SEM鉴别膜的晶体结构及观察膜的形貌和厚度;通过单气体的渗透测试表征气体传递特性.结果显示,陈化对膜的晶粒大小、晶体互生性以及表面覆盖度有着重要的影响;陈化2天后晶化形成的NaX沸石膜对H_2/N_2的渗透通量及理想选择性最高分别可达37/10 mol/(m~2·Pa·s)和110.     

Influence of metal substrate properties on the kinetics of zeolite film formation

The primary stages of zeolite Y and silicalite-1 film formation on both untreated and plastically deformed copper substrates are considered from the viewpoint of the film growth kinetics and morphology. Experimental results indicate a satisfactory agreement between the kinetic and profilometric data.     

Thoughts on the induction time in zeolite crystallization

The analysis and mechanistic interpretation of the induction time observed in typical zeolite crystallizations are given. In particular, it is shown that analyzing zeolite crystallization with constant supersaturation models ignores the lag time resulting from solution rearrangements and yields inappropriately high dependence of crystallization on time. Furthermore, it is shown that the phenomenon of size-dependent crystal solubility, expressed as the Kelvin effect, is not the cause of the aforementioned lag time.     

晶化处理温度对钛系凝胶光催化降解性能的影响

采用溶胶-凝胶法制备了掺Pb和Si的TiO2纳米粒子,用XRD和UV-VIS检测技术对所制的样品进行了表征.以苯酚的光催化降解为对象,考察了晶化处理温度及掺Pb、Si对材料结构、组成和光催化性能的影响;结果表明,掺入Pb、Si提高了TiO2纳米粒子中锐钛矿和金红石的晶化温度,TiO2纳米粒子的光催化活性得到较大的提高.在900℃进行晶化处理的SiTiPb复合凝胶的光催化活性最优.     

Influence of zeolite structure and chemistry on the electrical response and crystallization phase of poly(vinylidene fluoride)

Zeolites with framework types LTL, LTA, FAU, and MFI were synthesized and used as fillers to prepare PVDF/zeolite composites. The obtained composites showed structural and electrical dependence on the pore system and chemical content of the inorganic host. The larger polymer-zeolite electrostatic interactions of the Y and A zeolites lead the polymer to crystallize in the electroactive γ-phase, which in the case of the L zeolite is prevented due to the reduced interaction area. The solvent and water encapsulation ability of the zeolite as well as improve of the dielectric response of the composite is directly related to the Si/Al ratio, leading zeolites with lower Si/Al ratios to larger dielectric responses and encapsulation efficiencies in the composites. These effects show also some dependency on the dimensionality of the pore system; the zeolite L-containing 1D channels showing superior dielectric performance than the 3D pore system of zeolite Y.     

Influence of iron and temperature on the crystallization of calcium phosphates at the physiological pH

The effect of iron and temperature on the crystallization of dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) in agarose was studied at various temperatures (27, 37 and 47 °C) at the physiological pH (7.4) by the single diffusion method. The spherulitic crystals of hydroxyapatite with a diameter of about 3 mm were observed in the presence of Fe at temperature of 47 °C. The spherulites consisted of thin, elongated needlelike crystals. Quantification of the iron incorporated in the crystals was carried out by elemental analysis. The crystals were characterized by XRD, FTIR and SEM techniques.     

Synthesis of titanium silicate ETS-10: The effect of tetrametylammonium on the crystallization kinetics

Titanium silicate ETS-10 was synthesized from titanosilicate gels in the presence of an organic template—tetrametylammonium (TMA) chloride—at temperatures of 160, 180, and 200°C. The kinetic analysis of the crystallization of ETS-10 permits us to follow the role of the used template during the consecutive steps of the process. The presence of TMA diminishes the nucleation time and acclerates the crystal growth. The incorporation of TMA in the channel system of titanium silicate changes significantly the crystal morphology of ETS-10.     

Studies on the crystallization process of BEA/MOR co-crystalline zeolite

BEA/MOR co-crystalline zeolite was synthesized using tetraethylammonium-fluorides as composite templates. The crystallization process of BEA/MOR co-crystalline zeolite was systematically investigated based on XRD, ICP, SEM, TGA, and nitrogen adsorption characterizations. Through the XRD patterns of the samples with different crystallization times, the BEA and MOR phases did not appear simultaneously in the crystallization process. The BEA phase was the favored product at the beginning of crystallization, whereafter the MOR phase emerged, and the BEA/MOR co-crystalline zeolite was gradually formed. The morphology of obtained particles changed a little during the crystallization process, but the granularity distribution range broadened. Asymmetry of BEA/MOR co-crystalline zeolite particles led to uneven distribution of the mesopores. It is showed that the pore size distribution of the samples with more than 90-h crystallization period exhibited bimodal mesopores distribution, and the pore sizes of the extra mesopores were 4.9 and 5.6 nm, respectively. Based on these results, the crystallization mechanism of BEA/MOR co-crystalline zeolite in tetraethylammonium-fluoride binary templates was roughly proposed.     

The effects of the silica source on the crystallization of zeolite NaX

The effects of varying the starting silica source on the synthesis of molecular sieve zeolite NaX were investigated, while all other reaction parameters were kept constant. The silica sources were all powders of varying types and purity. Characterizations of the silica sources, the silicate solutions, and the synthesis products were completed by powder X-ray diffraction, electron microscopy, particle-size analysis, n.m.r, spectroscopy, laser light scattering, and elemental analysis. The use of different silica sources significantly influenced the outcome of the synthesis experiments. There were large differ- ences in the results from the various batch synthesis mixtures, even though the batch compositions were all the same (neglecting impurities). The experiments, all conducted at 115°C in sealed 6 ml autoclaves, yielded products of different particle sizes, different amounts of impurity zeolite phases, and different conversion rates to zeolite NaX. The n.m.r. spectra of the dissolved silica sources were all effectively the same; however, the levels of trace impurities were very different. The extent to which nuclei formed in these experiments was shown to correlate to the impurity level of any one of several elements in the silica sources, but not to the turbidity of the filtered solutions as noted by a simple light-scattering measurement.     

Use of pH-measurements to monitor zeolite crystallization

The crystallization of zeolites from alumino-silicate gels is usually accompanied by a change in pH and hence pH measurements can be used as a simple rapid method for following the course of the reaction. The method is particularly suitable for investigations into the synthesis of high silica zeolites and can be used both to give mechanistic information and to establish when crystallization of the desired phase has been completed.     

The role of triethanolamine in zeolite crystallization

The role of triethanolamine (TEA) in zeolite NaA synthesis systems was investigated. Particle-size analyses on products formed in the presence of the amine revealed that TEA affected the nucleation and crystallization rates to some extent. Crystallization studies carried out in reduced aluminum and aluminum-free systems suggested an aluminum complexing role for TEA. The existence of a complex was confirmed by solution-phase ¹³C n.m.r. spectroscopy. Synthesis studies using close analogs of TEA revealed that all three hydroxyl groups as well as the amine group in TEA were necessary for successful complexation and nucleation suppression. Differential scanning calorimetry carried out on products crystallized in the presence of the amine showed that TEA did not act as a void filler during zeolite NaA crystallization.     

无机盐对4A沸石晶化过程的影响

研究了添加无机盐氯化钠(NaCl)对4A沸石晶化速度以及粒度的影响。结果表明,添加一定量的NaCl并且随着NaCl加入量的增加,能够缩短4A沸石的晶化诱导期,加快晶化速率,减小4A沸石的粒度,使其粒度分布变窄。从电镜照片可以看出,加入NaCl合成的4A沸石晶体为正方形,晶体粒度比不加NaCl合成的4A沸石粒度小,并且随着NaCl加入量的增加,4A沸石晶体粒度明显减小。