Influence of the incorporated metal on template removal from MCM-41 type mesoporous materials

Al-modified MCM-41, La-modified MCM-41, and Ce-modified MCM-41 mesoporous materials were prepared with different molar ratios (Si/M = 10; 25; 50; 100 and 200) at room temperature. The materials were characterized using XRD, BET–BJH, and TG–DTA. The XRD showed four peaks, due to the ordered hexagonal array of parallel silica tubes, which could be indexed as (100), (110), (200), and (210), assuming a hexagonal unit cell. The surface area decreased as the concentration of the metal incorporated in the material increased. The thermal stability of the materials was around 650 °C. The CeO₂ phase made the mass transfer process more difficult, hindering Hofmann degradation and favoring oxidation.     

Rapid synthesis of highly ordered Si-MCM-41

A very short-time synthesis of highly ordered MCM-41 molecular sieve was formulated by using cetyltrimethylammonium bromide (CTAB) as the template and silica gel from SiliCycle as the silica source. The physical properties of MCM-41 samples were characterized by X-ray diffraction (XRD), nitrogen physisorption, and transmission electron microscopy (TEM). The MCM-41 sample prepared in this study exhibited well defined long-range order and good hydrothermal stability. It was demonstrated that reducing the time of self-assembly step to 2 h during the synthesis had no unfavorable effect on the quality of MCM-41 materials.     

AlMCM-41介孔分子筛的合成及表征

以拟薄水铝石为铝源、水玻璃为硅源、十六烷基三甲基溴化铵为模板剂,在110℃时水热晶化合成了含Al的MCM-41介孔分子筛.采用X射线衍射(XRD)、N2吸附-脱附、固体29Si、27Al魔角旋转核磁共振技术(MASNMR)、扫描电镜(SEM)及吡啶吸附傅里叶变换红外(FTIR)光谱技术对AlMCM-41分子筛进行了表征.结果表明:AlMCM-41分子筛具有六方排列的孔道结构,同时具有很高的相对结晶度、比表面积和孔容,且孔分布单一;AlMCM-41分子筛中Si原子在骨架内键合的程度更高,使AlMCM-41分子筛具有更好的骨架晶化程度;同时具有四配位骨架铝,使AlMCM-41介孔分子筛具有适当的酸性.     

Degradation and adsorption of rhodamine B and phenol on TiO<Subscript>2</Subscript>/MCM-41

TiO₂/MCM-41 composites with various titania content were prepared by loading titania into the mesopores of MCM-41 molecular sieves by sol-gel method, and were used as photocatalysts to degrade Rhodamine B (RhB) and phenol. The efficiency of organic contaminants removal was increased significantly compared with pure TiO₂. Ti/Si ratio, namely, the content of TiO₂ was determined by ICP-AES method. TiO₂/MCM-41 composites were characterized by X-ray diffraction, UV-Vis absorption spectroscopy and N₂ adsorption techniques. Experimental results demonstrated that most of the RhB was adsorbed instead of being degradated by TiO₂/MCM-41 due to the large specific surface area of MCM-41, while most of phenol was degradated. It turned out that the TiO₂/MCM-41 with the highest Ti/Si ratio of 0.8220 (wt) had the highest catalytic activity.     

Synthesis and characterization of M-MCM-48 (M = Cr,Ce) from silatrane via sol–gel process

Chromium and cerium incorporated into MCM-48 framework are hydrothermally synthesized via sol–gel process without any additives and characterized by X-ray diffraction, N₂ adsorption/desorption, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Diffuse reflectance UV–vis spectroscopy, and Thermogravimetric analysis. Results indicate that the materials possess a long-range ordered structure, high specific surface area, and narrow pore size distribution. SEM images illustrate the edge-truncated octahedron morphology of Cr-MCM-48 while Ce-MCM-48 preserves the truncated octahedron of the MCM-48 parent material. TEM images show the pore network of Ia3d symmetry after loading metals. Spectroscopic data confirm the existence of metals in the framework and extra-framework. At low Cr content, Cr-MCM-48 contains only Cr(VI) species while rich Cr content loading results in both the Cr(VI) and Cr(III) species. The hydrothermal stability of MCM-48 is enhanced by carefully incorporating metals into the parent material.     

Thermal and Microchemical Characterisation of Sol-Gel SiO2, TiO2 and xSiO2–(1–x)TiO2 Ceramic Materials

Amorphous SiO₂, TiO₂ and xSiO₂–(1–x)TiO₂ ceramic materials with selected values of x 0.5, 0.7 and 0.9, have been prepared via sol-gel process using silicon tetraethoxysilane (TEOS) and titanium tetraisopropoxide Ti(OPri)₄. By means of the combined use of differential thermal analysis (DTA),thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM),X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy(XAES), the surface microchemical structure and morphology of the sol-gel materials have been studied as a function of thermal treatments carried out in air up to 1200°C. In the range of temperature from 50 to 450°C, DTA-TG results evidence a remarkable mass loss due to the evaporation of organic solvents entrapped in the sol-gel materials and of the remnant organic components of the precursor metal alkoxides. In the range of temperature from 400 to about 1000°C, by means of the combined use of DTA, XRD, XPS and XAES techniques as a function of temperature and of chemical composition, it is possible to evidence the formation of crystalline phases such as quartz, anatase and rutile. Furthermore, line shape analysis of O1s XPS peak allows to distinguish between single O–Ti and O–Si bonds and also to disclose the presence of cross linking Si–O–Ti bonds, that act as bridges between SiO₂and TiO₂ moieties. As a function of temperature, Si–O–Ti bonds are broken and the formation of new Ti–O and Si–O bonds as in TiO₂ and SiO₂takes place as well as a silica segregation phenomenon. This revised version was published online in July 2006 with corrections to the Cover Date.     

Organic-inorganic hybrid materials based on N=C=O functionalised silan modified with titanium and zirconium

This work investigates the influence of the precursor trimethylsilil isocyanate on the sol-gel synthesis of hybrid materials. The obtained Si−O−C−N network is additionally modified by titanium and zirconium alcoxypropoxides in the range of 10 to 30 wt. %. The structure of the obtained hybrid materials before and after pyrolysis up to 1100°C was investigated by methods of XRD, FTIR and ²⁹Si MAS NMR. We established that the hybrid structure was stable up to 600°C based on IR study. The structural transformation of the hybrid materials into oxycarbonitrogen system started at 800°C. The network of the hybrids modified by titanium remained stable and amorphous up to the final temperature of the pyrolysis (1100°C) compared to the gels modified by more than 10 wt.% Zr. It was confirmed by XRD analysis that the last mentioned are nanocomposite materials, built from carbooxynitrogen vitreous matrix and ZrO₂-nanocrystals (tetragonal). The NMR method verified the presence of heterometallic bonds (Si−O−Ti and Si−O−Zr) and Q₄, ZrQ₃ or TiQ₃, NSiO₃ and D structural units in the gels.     

高钛含量钛硅中孔材料的合成及理化性质研究

通过单独水解混合成胶在静态条件下采用水热晶化及水热后处理,在模版剂用量较低和n(Ti)/n(Si)高达1/4的条件下合成了钛硅中孔材料.XRD、FT-IR、UV-Vis DRS和催化选择氧化反应表征结果表明,新合成方法有效防止了成胶过程在高钛含量下产生不溶性钛硅物种,合成产物呈高度有序的MCM-41六方结构,并具有较高的热稳定性和催化选择氧化反应活性.四丁基氢氧化铵在成胶过程不仅有利于钛形成稳定的可溶性物种从而提高其利用率,同时还促进孔墙内基本结构单元的交联和有序化.     

Synthesis, characterization, and catalytic properties of stable mesoporous molecular sieve MCM-41 prepared from zeolite mordenite

Mesoporous molecular sieves (denoted as M-MCM-41) with ordered hexagonal structure have been successfully synthesized from the assembly of precursors from preformed zeolite Mordenite with CTAB surfactant micelle in alkaline media. The samples were characterized by XRD, N₂ adsorption, IR and DTG. The materials exhibit highly hydrothermal stability, as compared with conventional MCM-41. Characterization results indicate that the mesoporous walls of M-MCM-41 contain the secondary building units similar to those in microporous crystal of zeolite Mordenite. In catalytic dealkylation of C10⁺ aromatic hydrocarbon, M-MCM-41 shows higher activities in comparison with Mordenite and MCM-41, which would be ascribed to the combination of advantages of both MCM-41 (large pores) and Mordenite (strong acidity). Furthermore, this synthesis strategy could be used as a new general method for the preparation of hydrothermally stable mesoporous aluminosilicate materials under alkaline conditions.     

Amine functionalized MCM-41: An active and reusable catalyst for Knoevenagel condensation reaction

This paper reports preparation, characterization of amine modified mesoporous crystalline MCM-41 and its application in Knoevenagel condensation reaction. Amine modified MCM-41 was prepared by co-condensation and post-synthesis methods. The samples were characterized by X-ray powder diffraction, Fourier-transfer infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron micrograph (SEM), ²⁹Si magic-angle spinning (MAS), nuclear magnetic resonance (NMR), diffuse reflectance spectra (DRS), nitrogen adsorption–desorption and CHN analysis. X-ray diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. SEM study exhibits that the arrangement of particles for 12.8% amine modified MCM-41 is well ordered and spherical in nature. CHN analysis supports that complete hydrolysis of ethoxy groups take place in 12.8% amine modified sample. From the NMR study it is confirmed that the surface coverage is 40% in 12.8% amine modified sample. The base catalytic activity of hybrid MCM-41 materials such as amine (post-synthesis and co-condensation methods) and surfactant functionalized materials for condensation reaction between benzaldehyde and diethyl malonate in solvent free, room temperature synthesis of cinnamic acid was evaluated and correlated with the surface and textural properties. Sample containing 12.8 wt% amine loaded by co-condensation method showed highest malonic ester conversion (92%) and selectivity (98%) for cinnamic acid.     

以十六烷基三甲基溴化铵为模板剂合成MCM-41/ZSM-5复合分子筛的研究

采用阳离子表面活性剂十六烷基三甲基溴化铵(CTAB)为模板剂、以ZSM-5为晶种,在水热晶化条件下合成了同时具有微孔和介孔的MCM-41/ZSM-5复合分子筛;并考察了陈化温度、陈化时间、晶化时间及模板剂用量等条件对合成复合分子筛的影响.通过X射线衍射、扫描电镜、高分辨率透射电镜、红外光谱及N2静态吸附法等手段对合成样...     

Facile H2O2 Hydrothermal Synthesis of Bimodal Mesoporous Silica MCM-48 Spheres

The ordered bimodal mesoporous silica MCM-48 spheres were facile synthesized by mild-temperature post-synthesis H₂O₂ hydrothermal treatment of as-synthesized MCM-48. The results showed that H₂O₂ is indispensable for simultaneously removing organic templates and forming ordered bimodal mesoporous silica MCM-48 spheres. The bimodal mesoporous MCM-48 was characterized by X-ray diffraction, transmission electron micrographs, FT-IR, and N₂ adsorption-desorption, and a possible mechanism was proposed for the formation of bimodal mesoporous MCM-48.     

Synthesis of [Si]-MCM-41 from TEOS and water glass: the water glass-enhanced condensation of TEOS under alkaline conditions

Mesoporous [Si]-MCM-41 molecular sieve systems have been fabricated by aging silica gels in CTAB both at RT and under hydrothermal conditions with or without stirring. For the synthesis involving water glass as a SiO₂ source, optimal conditions (100 °C, pH 10, crystallization time 2–3 days) gave reproducible, highly ordered [Si]-MCM-41 materials in multi gram scale with high lattice parameter values and BET surface areas. The synthesis with TEOS as silica source produced an inferior quality material. A novel synthesis route involving the use of mixtures of the two precursors gave [Si]-MCM-41 with improved structural (XRD) and microstructural (HRTEM) long-range order. Addition of small amounts of water glass to a TEOS-based synthesis gel under stirred conditions produced [Si]-MCM-41 with excellent mesoporosity, long-range microstructural order, XRD and S _BET properties. These properties are reminiscent of those for materials obtained from water glass as a sole SiO₂ source. The advantage of this route is that it gave high-quality materials at relatively lower temperatures (80 °C) and shorter crystallization times (6 h) after 21 h aging at RT. The variation of the XRD d ₁₀₀ peak position, BET and HRTEM properties with [TEOS]/[water glass] ratio revealed that a ratio = 3.95 gave optimal production of the highly ordered materials. The data suggests that water glass acts as a structure-directing agent for the TEOS and is incorporated into the final structure.     

An ultra-low hydrolysis sol-gel route for titanosilicate xerogels and their characterization

In this work TiO₂-SiO₂ xerogels were prepared through an ultra low hydrolysis method using titanium and silicon alkoxide. The samples were heat treated to 500°C. The xerogels were characterized using TGA/DTA, FTIR, XRD and TEM. The samples showed the formation of Si–O–Ti bridges by its characteristic vibration within 925–960 cm⁻¹ range. Si–O–Si bond angles were calculated using the central force network model. The TiO₂ in all the samples crystallized on heat treatment to 500°C. The crystallite size calculated using the Scherer formula from the XRD was verified from the Transmission Electron Micrograph. Samples heat treated to 350°C remained amorphous and hence could be used as hosts for biomaterials and organic optical materials.     

介孔分子筛MCM-41的水热稳定性

介孔分子筛MCM-41在催化、吸附分离以及化学组装制备先进材料等方面具有潜在的巨大应用价值,但MCM-41的低水热稳定性使其在催化研究领域中的应用受到了极大的限制。因此,提高介孔分子筛的水热稳定性具有十分重要的科研和实际应用意义。笔者对介孔分子筛MCM-41低水热稳定性的原因作了简要分析,并系统地介绍了近几年来在提高介孔分子筛水热稳定性方面的研究工作。     

介孔材料Co-MCM-41的合成及其吸附脱除各种碱性氮化物

采用水热法合成了MCM-41和不同Co/Si物质的量比的Co-MCM-41介孔材料,并采用XRD、FT-IR和低温氮气吸附-脱附方法对样品进行了表征。FT-IR及XRD表征结果说明,Co原子已经进入了介孔材料的孔壁。合成的MCM-41及Co/Si(物质的量比)为0.18以下的Co-M CM-41都具有六方有序排列的介孔结构。当加入的Co/Si(物质的量比)为0.22时,样品的(100)峰完全消失,不具备六方有序排列的介孔结构,说明以硝酸钴为钴源合成Co-MCM-41的最大Co加入量为Co/Si(物质的量比)为0.18左右。与MCM-41相比,各Co-MCM-41样品的XRD(100)峰随着Co加入量的增加逐渐变宽变弱,比表面积和孔容变小,平均孔径增大。当加入的Co/Si物质的量比大于0.06时,Co-MCM-41的介孔孔道中存在少量聚集态的Co3O4。利用合成的Co-MCM-41吸附脱除氮含量为1737.35μg/g模拟燃料中的碱性氮化物喹啉、苯胺或吡啶,结果表明,所有样品的吸附脱氮效果顺序为苯胺吡啶喹啉。Co-MCM-41(0.06)的吸附容量和氮脱除率明显要高于其他样品,对苯胺、吡啶和喹啉的吸附容量分别为42.17、35.66和29.18 mg(N)/g,去除率分别为82.38%、73.53%和61.11%。添加到模拟燃料中的芳烃化合物萘、苯或甲苯对其吸附脱氮没有影响,表明介孔材料Co-MCM-41对各种含氮化合物的吸附主要是N原子与Co的配位络合吸附,而不是π-π络合作用。采用焙烧或乙醇溶剂洗涤再生后的Co-MCM-41(0.06)恢复了吸附脱氮能力,说明其具有较好的再生性能。     

新戊基钛在MCM-41表面的接枝反应及产物性质

采用原位红外光谱法在真空系统中考察了MCM-41分子筛表面与四新戊基钛Ti(CH2CMe3)4的反应,发现这个反应可在室温下定量进行,得到表面新戊基钛(≡Si－O)2Ti(CH2CMe3)2. 这种表面新戊基钛很容易与CH3OH、H2O和O2进一步发生反应分别得到(≡Si－O)2Ti(OCH3)2、(≡Si－O)2Ti(OH)2和(≡Si－O)2Ti(OCH2CMe3)2等表面化合物.在氧气中焙烧由(≡Si－O)2Ti(CH2CMe3)2水解所得的(≡Si－O)2Ti(OH)2可制得表面含钛MCM-41介孔分子筛（Ti-MCM-41）.元素分析、低温N2吸附-脱附、紫外可见漫反射光谱、X射线粉末衍射和FTIR等表征结果表明,接枝反应和后续的处理不破坏分子筛的介孔结构; Ti-MCM-41的比表面积和孔直径较MCM-41略有降低; Ti原子在Ti-MCM-41表面以TiO4四面体配位状态分散,并对乙烯氧化有较明显的光催化活性.论文还通过对Ti-MCM-41与水热合成骨架含钛[Ti]-MCM-41结构和光催化活性的比较,对分子筛类材料光催化作用机制进行了分析探讨.     

MCM-41介孔材料负载金属的一步法合成及其对酯化反应的催化作用

以增溶了茂金属的十六烷基三甲基溴化铵(CTAB)胶束为模板, 采用一步法合成了介孔表面负载有金属(铁、钛和锆)的介孔材料MCM-41, 通过等离子体电感耦合发射光谱仪(ICP-AES)测定铁、钛和锆负载量(质量分数)分别为1.71%、0.95%和0.81%. 通过X射线衍射(XRD)图谱和N₂吸脱附等温线可知, 负载金属的介孔材料M-MCM-41(T) 仍具有较高的比表面以及规整的六方有序孔道结构, 去除模板剂的焙烧温度对孔道结构有一定影响. 由一步法合成的金属负载介孔材料对乙酸正丁酯的酯化反应具有很高的催化活性, 其中Fe-MCM-41在单位时间单位金属催化生成的产物量(TOF)为55643 g·h^-1·g^-1, 而Zr-MCM-41的TOF高达125320 g·h^-1·g^-1. 与纯茂金属相比, 由茂金属合成的金属负载介孔材料可显著提高酯化反应的催化活性.     

高负载钛MCM-41催化剂的制备与表征

钛硅分子筛在各种有机反应中具有独特的催化氧化性能，采用廉价双氧水作氧化剂，产物选择性高，反应条件温和，不会发生深度氧化，且整个催化反应无污染排放，所以越来越受到人们的重视．然而TS—1以及其它微孔分子筛的孔径较小，难以使大分子的有机化合物进人孔道中进行催化反应，因此合成较高水热稳定性及高氧化活性的介孔钛硅分子筛仍是催化研究的重要课题。     

Selective synthesis of α-substituted β-keto esters from aldehydes and diazoesters on mesoporous silica catalysts

The titled reactions are effectively catalyzed on mesoporous silica MCM-41 but not on amorphous silica prepared from the same starting materials as those of MCM-41. The ordered porous structure was essential to generate the acid catalysis. Planting of Al or Ti ion improved not only the catalytic activity but also the tolerance to basic functional groups of substrates. The catalytic activity of Al- or Ti-MCM-41 was better than that of SnCl₂ and NbCl₅ in the homogeneous phase. In particular, Al (or Ti)-MCM-41 was characteristically active for the reaction of aldehydes with α-substituted diazoesters to give 2-substituted-3-oxo propionic acid esters.