预吸附微波合成纳米NaY沸石晶种制备NaY型分子筛膜

在常压回流的微波加热体系中成功地合成出纳米尺寸的NaY分子筛,XRD和SEM等表征结果表明,分子筛具有40nm左右的平均晶粒尺寸.以其为晶种,预吸附在多孔氧化铝载体上,结合原位水热法进行二次晶化,制备出较为致密的NaY分子筛膜,该膜主要以孪生聚晶的形式存在.CO₂/N₂气体分离测试结果显示,随着温度的升高,分子筛膜的气体分离能力呈上升趋势,在140℃时真实选择分离系数达到最大值4.0.     

核壳MFI/CHA分子筛的合成及催化性能

采用二次生长法(外延法)在ZSM-5(MFI型)晶体颗粒表面外延生长SAPO-34(CHA型)磷酸硅铝分子筛壳层,合成了MFI/CHA型核壳分子筛材料。并利用X射线衍射(XRD)、扫描电镜(SEM)、能量色散射线光谱(EDS)和傅里叶变换红外(FTIR)光谱对其进行了表征。结果表明,核相ZSM-5的预处理步骤对于成功合成此核壳型分子筛材料十分关键。通过研究晶化温度和晶化时间对MFI/CHA核壳型沸石分子筛合成的影响推测出MFI/CHA壳层生长的晶化机理,并考察在甲醇芳构化中的择形催化作用。     

非碱性介质中分子筛的合成

分子筛的合成通常是采用含碱金属离子的强碱性体系,通过水热晶化法实现~[1,2]的.得到的分子筛原粉不但必须通过铵离子交换和焙烧才能转变为氢型催化剂,而且在该体系中晶体的粒度也较小.Guth等人~[3]首次报道了在非碱性介质F-离子存在下直接合成铵型ZSM-5的工作.除用四丙基溴化铵合成ZSM-5及其杂原子分子筛外~[4],尚未见到在非碱性介质中合     

无溶剂法合成ZSM-5/SiC整体式催化剂制备生物燃料

传统合成整块载体负载分子筛催化剂的方法是水热法,这样往往伴随水资源浪费和釜内空间利用率低的问题.本文报道了应用无溶剂法在蜂窝结构的碳化硅(SiC)表面原位生长ZSM-5分子筛.进一步采用该法将Pd纳米粒子限域在ZSM-5分子筛内,合成Pd@ZSM-5/SiC双功能催化剂,并在油酸甲酯加氢反应中表现出较高的活性和高碳烷烃选择性.结果发现,Pd@ZSM-5/SiC表现出高选择性和耐久性,这归因于SiC优异的传质和导热特性.X射线衍射、扫描电子显微镜和氮气吸附等结果表明,通过无溶剂法合成的分子筛具有很高的结晶度和纯度;高分辨透射电镜结果表明,在Pd@ZSM-5和Pd@ZSM-5/SiC催化剂中,Pd纳米粒子均被良好封装,并且粒径无明显差别,因此排除金属活性中心粒径的干扰.油酸甲酯的直接加氢脱氧/脱羧可以制备具有高附加值的长链碳氢化合物,而碳氢化合物的裂解通常会伴随着低碳化合物等副产物的生成.我们比较了两种催化剂在350-500℃的转化率和高碳烷烃的选择性差异.在相同反应条件下,Pd@ZSM-5/SiC催化剂上油酸甲酯转化率始终高于Pd@ZSM-5.例如在450℃,Pd@ZSM-5和Pd@ZSM-5/SiC的转化率分别为97.6%和78.2%,当温度提升至500℃,Pd@ZSM-5/SiC将油酸甲酯完全转化,而Pd@ZSM-5的转化率仅为88%.在350℃时,Pd@ZSM-5/SiC以脱羧反应为主,其中C17和C18的选择性分别为67.3%和20.1%,C6-12和C13-16选择性分别为2.4%和5.0%.相比之下,Pd@ZSM-5催化剂C17的选择性为39.4%,C18的选择性为13.2%,C6-12和C13-16选择性分别为20.2%和20.6%.由此可见,Pd@ZSM-5对于高附加值的长链碳氢化合物的选择性远低于Pd@ZSM-5/SiC;这可能与在Pd@ZSM-5催化剂上更容易发生烷烃裂解副反应有关.值得注意的是,虽然升高温度会促进碳氢化合物的裂解,但是在Pd@ZSM-5/SiC催化剂上高碳化合物依然较多.例如,在500℃时,裂解是Pd@ZSM-5催化剂上的主要反应,C1-5的选择性高达50.1%,C6-12的选择性高达37.0%;而在Pd@ZSM-5/SiC的产物中,C13-16的选择性为40.0%,C17-18的选择性更是高达16.7%.此外,在450℃的油酸甲酯加氢连续实验中,Pd@ZSM-5/SiC比Pd@ZSM-5表现出更好的耐久性,且催化剂失活后可以通过焙烧手段再生.上述结果表明,Pd@ZSM-5/SiC催化剂有利于加氢脱氧/脱羧反应制备有价值的高碳烃产品,更能抑制裂解副反应的进行.相比之下,传统的粉末催化剂对裂解产物仍具有较高的选择性,尤其是在较高的反应温度下.SiC载体的引入有利于高碳产物的传质,从而抑制了裂解反应.此外,碳化硅良好的导热性可以有效地防止催化剂在反应中的过热,同样有利于抑制碳氢化合物的裂解.     

Preparation and characterization of alumina supported silicalite membranes by sol–gel hydrothermal method

Two types of unsupported zeolites (silicalite-1 and silicalite-2) and porous alumina discs supports were prepared by the hydrothermal sol–gel synthesis method. The influence of the raw materials used as SiO₂ source, the temperature of the thermal treatment and the presence of the ceramic support on the crystallization of zeolites were studied. The reaction products were characterized by X-ray diffraction (XRD), IR spectroscopy (IR) and scanning electron microscopy (SEM) studies. The SiO₂ source had a significant effect on the final zeolite obtained: the use of colloidal silica sol (ZCS) as SiO₂ source in the synthesis led to ZSM-11 (silicalite-2) crystals, while the sodium silicate solution (ZSS) produced the ZSM-5 (silicalite-1) type. The presence of the alumina support influences the crystallization process of ZSM-5, as it improves nucleation and the ordering of the crystals.     

Fabrication of b‐Oriented MFI Zeolite Films under Neutral Conditions without the Use of Hydrogen Fluoride

The fabrication of MFI zeolite films with particular b‐axis orientation is especially fascinating. Unlike the conventional alkaline or hydrofluoric acid (HF) assisted neutral synthesis route, here we develop a novel neutral synthesis solution system of TPABr/fumed silica/H₂O without the use of HF and successfully synthesize highly b‐oriented MFI zeolite films on glass‐plate substrates by secondary growth. The localized weak alkaline environment created by the dissolved Na₂O species from the substrate is identified as the key factor for the depolymerization of fumed silica and subsequently the in‐plane growth of zeolite seed layers. Continuous b‐oriented MFI films can also be synthesized on other substrates in the presence of a glass plate or a trace amount of NaOH, which making our neutral synthesis route promising for the direct synthesis of MFI zeolite films and membranes on various substrates.     

Bread-template synthesis of hierarchical mesoporous ZSM-5 zeolite with hydrothermally stable mesoporosity

A hierarchical mesoporous ZSM-5 zeolite has been synthesized by using starch-derived bread as a meso-template. The obtained mesoporous ZSM-5 was characterized with X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric (TG)/differential thermal analysis (DTA) techniques. Hydrothermal treatments revealed that the mesoporosity in hierarchical mesoporous ZSM-5 exhibited excellent hydrothermal stability. Catalytic tests showed that hierarchical mesoporous ZSM-5 was more active than conventional zeolite of ZSM-5 in catalytic cracking of 1,3,5-tri-isopropylbenzene. Hydrogen adsorption measurements showed hierarchical mesoporous ZSM-5 had a higher storage capacity than the conventional ZSM-5.     

One-step synthesis of hierarchical aluminosilicate aggregates using bifunctional alkanolamine as single template

Highly active, hierarchical zeolite ZSM-5 aggregates have been prepared in a one-step synthesis using alkanolamine as single template. The effects of SiO₂/Al₂O₃, pH and H₂O/SiO₂ on the aggregate morphology of the ZSM-5 nanocrystals were investigated. The obtained aggregate zeolites characterized by SEM, TEM and BET possessed significant textual porosity (up to 0.22 cm³/g), which could be tuned by the number of substituents in the alkanolamine molecules and the amount of aluminum in the synthetic mixtures. These zeolite aggregates showed high activities for Friedel–Crafts alkylations and may curtail the filtration difficulties during the synthesis and applications to some extent.     

Synthesis of NaX and NaY Zeolites from Tunisian Kaolinite as Base Catalysts: An Investigation of Knoevenagel Condensation

The synthesis of Faujasite‐type zeolites with high purity has been successfully performed from Tunisian kaolinite and the effects of different crystallization parameters on the final products were widely investigated. The alkaline fusion of kaolinite followed by hydrothermal treatment lead to zeolite NaX synthesis whereas the classic hydrothermal transformation of metakaolinite produces NaY zeolite. The results show that an increase in the synthesis temperature and time has improved the crystallization process of the zeolite NaX whereas the SiO₂/Al₂O₃ and the Na₂O/SiO₂ molar ratios were the key parameters to obtain a pure zeolite NaY. The highest specific surface areas obtained with the optimal crystallization conditions were 554 m2 g^?1 and 592 m2 g^?1 for respectively NaX and NaY zeolites. The basic properties of NaX and NaY zeolites were explored in the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate at 140 °C as a test reaction in the absence of solvent. The influence of ion exchange with cesium cation on the catalytic activity of prepared catalysts was also investigated. It was found that the NaX provided higher activity than that of NaY catalyst due to its lower Si/Al ratio whereas a cesium exchange conferred higher basicity to the prepared Na‐faujasite.     

亚硝胺在沸石上催化分解的研究

采用气相色谱 质谱（GC MSD）、程序升温表面反应（TPSR）和红外光谱（IR）技术研究吡咯烷亚硝胺（NPYR）和二甲基亚硝胺（NDMA）等亚硝胺在NaY、HY、NaZSM 5、HZSM 5等沸石上的催化分解,并剖析其产物分布,发现亚硝胺在Na＋型沸石上的裂解产物近似于热裂解,而在H＋型沸石上则发生了质子参与的催化裂解反应.     

Sustainable Synthesis of Core-Shell Structured ZSM-5@Silicalite-1 Zeolite

Core-shell structured ZSM-5@Silicalite-1 zeolite could effectively hinder the deactivation of catalyst surface. Currently, organic structure directing agents(OSDAs) are necessary in the conventional route for the synthesis of this core-shell zeolite under hydrothermal conditions, which is costly and environmental-unfriendly. In this research, a synthesis of the core-shell structured ZSM-5@Silicalite-1 zeolite with a strategy of alcohol filling and zeolite seeding without any organic template or solvent is exhibited. The obtained products are well characterized by X-ray powder diffractometer(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), N₂ sorption isotherms, solid magic angle spinning(MAS) NMR, temperature-programmed-desorption of ammonia(NH₃-TPD), and X-ray photoelectron spectroscopy(XPS) techniques, in order to confirm the core-shell structure. More importantly, the core-shell structured ZSM-5@Silicalite-1 zeolite exhibits a long lifetime and a high p-xylene selectivity in the alkylation of toluene with methanol, compared with the conventional ZSM-5 catalyst.     

Growth of ZSM-5 crystals within hollow β-zeolite

A zeolite composite composed of ZSM-5 andβ-zeolites has been synthesized by a procedure of the nucleation and crystallization of ZSM-5 zeolite in the hollowβ-zeolite.The property ofβ-zeolite crystals with aluminum-poor interior and aluminum-rich outer rim results in silicon extraction favorably in the aluminum-poor bulk rather than the aluminum-rich external surface.Subsequently,alkaline treatment ofβ-zeolite crystals during the second-step synthesis leads to a preferential dissolution of the aluminum-poor center and the formation of hollowβ-zeolite crystals.ZSM-5 zeolite crystals are therefore embedded and grown within the hollowβ-zeolite.The catalytic activities of Co-Hβ,Co-HZSM-5 and Co-HZSM-5/BEA are investigated during the reaction of methane catalytic reduction NO in the presence of O₂.     

环已胺在沸石分子筛上的吸脱附行为研究

本文以程序升温脱附(TPD)为主要实验手段,对环己胺在5种不同沸石分子筛上的吸脱附行为进行了研究。结果表明,沸石分子筛对环己胺有着较强的吸附作用,不同的沸石分子筛对环己胺的吸附能力受其结构和表面酸性特征的影响而异。有效吸附部位为与沸石分子筛表面酸性有关的弱化学吸附位;环己胺从不同沸石分子筛表面脱附的动力学与晶内扩散有关,其表观脱附活化能分别为:63.6kJ/mol(5A),68.6kJ/mol(13X),20.1kJ/mol(菱沸石),46.9kJ/mol(NaY)和47.3KJ/mol(ZSM-5)。     

Influence of template on crystallization of ZSM-5 zeolites

Pentasil zeolites of ZSM-5 type are synthesised hydrothermally using triethyl-n-proplyammonium bromide (TEPA-Br) and triethyl-n-butylammonium bromide (TEBA-Br). The crystallization kinetics, followed by XRD, SEM and thermal analysis, clearly demonstrate the influence of size and molecular weight of the templating quaternary ammonium cation (QAC) species on the rates of nucleation and crystallization. The values of the apparent activation energies for nucleation and crystal growth indicate that both nucleation and crystal growth are faster when TEPA-Br rather than TEBA-Br is used as a template. The quantitative identification of intergrown phases characterizes both the phases to be ZSM-5 zeolite. Thermoanalytical curves for both these zeolites in as-synthesised forms exhibit two-step oxidative decomposition of the occluded organic species. This suggests that the quaternary ammonium cation may be located at two energetically different sites within the zeolite channels. The equilibrium sorption capacity, however, is found to increase in the order of size and molecular weight of the templating species in both the zeolites. The nature of acid site distribution, obtained from the temperature programmed desorption of ammonia is found to be independent of the templating species used during the synthesis.     

含铁微孔EU-1/ZSM-5复合分子筛的合成和表征

采用预置晶种法合成了含铁的微孔EU-1/ZSM-5复合分子筛,并采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、热重-微分热重(TG-DTG)、N₂吸附-脱附、紫外-可见吸收光谱(UV-vis DRS)、X射线吸收精细结构(XAFS)等手段进行了表征。结果表明,复合分子筛具有EU-1和ZSM-5的特征衍射峰,是两种晶相相互作用的分子分散晶相材料,微孔孔径较Fe-EU-1分子筛有所增大。随原始溶胶中铁的质量分数增加,复合分子筛具有的23.09°和23.94°处的特征衍射峰逐渐向低角度方向偏移;紫外-可见漫反射谱图中在220~245 nm出现了宽的吸收谱带;XAFS表征表明,1s→3d电子跃迁的弱吸收峰逐渐增强,同时在吸收边顶部出现的1s→4p吸收峰逐渐由宽变窄。合成工艺的最佳条件为,原始溶胶中铁的质量分数为0.075%~0.15%,晶种添加比例为15.0%~21.0%,晶种SiO₂/Al₂O₃物质的量比为50~60。     

LiCl/NaY主客体复合材料的制备及其湿敏性质

利用热分散法将LiCl分散到NaY分子筛笼形孔道内制备了LiCl/NaY主客体湿敏材料,该材料保持了LiCl体相材料优良的湿敏特性,同时由于分子筛孔道的限域作用及LiCl盐与分子筛载体间的强离子键合作用,克服了LiCl体相材料的某些固有缺陷.分子筛结构对这种主客体材料有很大影响,具有笼形三维孔道结构的分子筛如NaY更适于作主体材料.二维孔道型的ZSM-5及一维直孔道的丝光沸石则效果差得多.     

高岭土原位无溶剂法合成小粒径ZSM-5分子筛

结合原位水热法和无溶剂法的优点,在不添加有机模板剂和溶剂的基础上,以高岭土为原料通过晶种诱导绿色高效地合成出ZSM-5分子筛。运用X射线衍射、N2吸附-脱附、扫描电镜、透射电镜和NH3程序升温脱附(TPD-NH3)等技术对ZSM-5分子筛进行表征。表征结果与原位水热法合成的ZSM-5分子筛相比,原位无溶剂法合成ZSM-5分子筛的结晶度较高、晶体粒径较小、酸强度略高、孔结构相似。     

Sol-Gel Routes to Zeolite Membranes and Thin Films

The synthesis of zeolite membranes and thin films using the secondary growth process is briefly described. In this process colloidal zeolite particles (sols) are prepared hydrothermally and then subsequently deposited on substrates to produce uniform layers of controlled thickness, as illustrated with silicalite and zeolite-A. The formation and growth of the zeolite sols has been investigated in situ by small angle neutron scattering (SANS). SANS measurements on silicalite sols at progressively higher concentrations have provided details of the colloid interactions which lead to zeolite gel-layer structures which are uniform and free of defects.     

醇盐水解法合成ZSM-5沸石

用正硅酸乙酯（ＴＥＯＳ）冰解作硅源、三氯化铝作铝源合成了ＺＳＭ－５沸石,并和传统的水玻璃作硅源合成ＺＳＭ－５法进行了比较。用ＸＲＤ、热重／差热分析、红外光谱和正己烷吸附等对实验产品进行了表征。醇盐水解法比传统方法结晶速度快,可缩短合成时间。新法合成的ＺＳＭ－５沸石结晶度高、憎水性强、晶粒易于取向生长,对合成沸石膜非常有利。     

The preparation and analysis of zeolite ZSM-5 membranes on porous alumina supports

Zeolite ZSM-5 particles formed in the synthesis solution assume a negative charge due to electrical double layer effects. Therefore, we investigated the use of electrophoretic techniques in addition to the hydrothermal synthesis method to attract the zeolite particles to the substrate surface before they precipitate out of the solution. This electrophoretic driving force produces a thin, continuous zeolite ZSM-5 membrane on the porous substrate. This research was conducted in order to produce zeolite membranes on a tubular support that could effect continuous gas phase separations. The thickness of membranes can be controlled by varying the precursor concentration, applied potential, and synthesis time. The selectivity of n-butane over iso-butane is observed on every membrane. The membranes were characterized by using scanning electron microscopy (SEM), X-ray diffractometry (XRD), and energy dispersive X-ray spectrometry (EDX).