Preparation and catalytic properties of new mesoporous materials

The development of ordered mesoporous solids is revised. Acid, base, and redox catalytic properties are presented together with their application for a series of organic reactions of fundamental and practical interest. Finally it is explained that it is possible to make use of the high surface and regular porosity of MCM–41 to prepare supported metals, and bifunctional catalysts. The above properties together with the presence of a large number of surface silanol groups allow the grafting of catalytically active transition metal complexes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Preparation and characterization of a titanium(IV) silsesquioxane epoxidation catalyst anchored into mesoporous MCM-41.

This paper describes the synthesis and spectroscopic study of a titanium(IV) silsesquioxane complex, which is heterogenised in the pores of an MCM-41 host material. Its immobilization is performed via chemical bonding, not by means of physical adsorption. As a linking molecule between the MCM-41 carrier and the silsesquioxane, (3-glycidyloxypropyl)trimethoxysilane is used. Characterization is performed by using nitrogen adsorption techniques, TGA, diffuse reflectance infrared spectroscopy (DRIFT) and ICP-MS. Also its catalytic activity towards the epoxidation of alkenes shows interesting results.     

Synthesis,characterization and catalytic properties of mesoporous MCM-48 containing zeolite secondary building units

Mesoporous aluminosilicate MCM-48 containing zeolite secondary building units in the pore wall has been synthesized in alkaline media with a two-step procedure. The aluminosilicate precursors comprising zeolite secondary building units were first synthesized by carefully controlling reaction conditions and then were assembled using co-templates of gemini surfactant [C₁₈H₃₇N(CH₃)₂(CH₂)₃-N(CH₃)₂C₁₈H₃₇]²⁺ (18-3-18) and triethanolamine (TEA). X-ray Diffraction (XRD) patterns of the as-made samples indicated that highly ordered mesostructured MCM-48 was formed. Transmission Electron Microscopy (TEM) images further verified the formation of MCM-48 with uniform cubic pore channel system having the pore opening diameter of about 25 ?. Compared with the conventionally synthesized MCM-48, the as-synthesized MCM-48 sample showed an adsorption band at 520–600 cm⁻¹ in its FT-IR spectrum, which was assigned to five-membered ring vibration from zeolite structure. This suggested the presence of zeolite building units in the pore wall. N₂ adsorption data showed that the material had a much higher specific surface area (1 200 m²/g) than the conventional MCM-48(1 100 m²/g). Finally, the catalytic performance of the as-made MCM-48 was evaluated by hydrogenation dealkylation reaction of heavy aromatic hydrocarbons. Catalytic results showed that the as-made MCM-48 catalyst exhibited higher conversion than the conventional MCM-48 catalyst. The as-made mesostructured MCM-48 may have a potential catalytic application in the conversion of bulky molecules. Translated from Journal of Fuel Chemistry and Technology, 2006, 34(1): 105–108 [译自: 燃料化学学报]     

Synthesis,characterization and catalytic properties of mesoporous MCM-48 containing zeolite secondary building units

Mesoporous aluminosilicate MCM-48 containing zeolite secondary building units in the pore wall has been synthesized in alkaline media with a two-step procedure. The aluminosilicate precursors comprising zeolite secondary building units were first synthesized by carefully controlling reaction conditions and then were assembled using cotemplates of gemini surfactant [C₁₈H₃₇N(CH₃)₂(CH₂)₃N(CH₃)₂C₁₈H₃₇]²⁺ (18-3-18) and triethanolamine (TEA). X-ray Diffraction (XRD) patterns of the as-made samples indicated that highly ordered mesostructured MCM-48 was formed. Transmission Electron Microscopy (TEM) images further verified the formation of MCM-48 with uniform cubic pore channel system having the pore opening diameter of about 25 Å. Compared with the conventionally synthesized MCM-48, the as-synthesized MCM-48 sample showed an adsorption band at 520 600 cm^-1 in its FT-IR spectrum, which was assigned to five-membered ring vibration from zeolite structure. This suggested the presence of zeolite building units in the pore wall. N2 adsorption data showed that the material had a much higher specific surface area (1 200 m₂/g) than the conventional MCM-48(1 100 m₂/g). Finally, the catalytic performance of the as-made MCM-48 was evaluated by hydrogenation dealkylation reaction of heavy aromatic hydrocarbons. Catalytic results showed that the as-made MCM-48 catalyst exhibited higher conversion than the conventional MCM-48 catalyst. The as-made mesostructured MCM-48 may have a potential catalytic application in the conversion of bulky molecules.     

A chiral diamine bis-phenolate complex of dioxomolybdenum(VI)

A new dioxomolybdenum(VI) complex with a chiral tetradentate ligand is reported. The tripodal ligand containing two nitrogen atoms and two phenolic oxygen atoms was synthesized starting from a chiral diamine precursor. Further reaction with [MoO₂(acac)₂] yielded a monomeric molybdenum complex as a bright yellow solid. The structures of the molybdenum complex and the free diamine bis-phenol ligand were determined by X-ray diffraction.     

Synthesis of tetradentate N4 Schiff base dioxomolybdenum (VI) complex within MCM-41 as selective catalyst for epoxidation of olefins

Covalent grafting of MCM-41 with 3-chloropropyl trimethoxysilane and subsequent reactions respectively with pypr [N,N′-bis(2-pyrrolmethylidenaminopropyl)amine] and complexation with MoO₂(acac)₂ afforded MoO₂pyprMCM-41. X-ray diffraction and nitrogen sorption analyses revealed the preservation of the textural properties of the support as well as accessibility of the channel system despite sequential reduction in surface area, pore volume and pore size. Elemental analyses showed nearly complete complexation of the supported ligands and the presence of 0.24 mmol molybdenum per gram of the catalyst. Epoxidation of cyclooctene, cyclohexene, 1-hexene and 1-octene in the presence of MoO₂pyprMCM-41 with tert-butyl hydroperoxide (TBHP) were carried out with 21–98% conversion under the mild reaction conditions.     

介孔MCM-48粉体对环氧树脂性能影响

采用溶液共混法制备了介孔MCM-48粉改性环氧树脂复合材料,研究了MCM-48添加量对复合材料力学性能及介电性能的影响。结果表明,添加少量的MCM-48粉能够同时对环氧树脂起到增强增韧效果。复合材料1MHz下的介电常数及介电损耗均随MCM-48添加量的增加先降低后升高。当MCM-48的添加量为2%时,复合材料的综合性能最佳,弯曲强度为82.15 MPa,弯曲弹性模量为2.45 GPa,冲击强度为21.75 kJ/m2,分别比纯环氧树脂提高了27.36%、28.32%、136.59%。复合材料1MHz下的介电常数为3.55,介电损耗为0.028。该材料有望在微电子领域获得应用。     

MCM-48固载杂多酸催化剂的孔结构与催化性能研究

以MCM-48介孔分子筛为载体、HSiW(硅钨杂多酸)为活性组分,采用浸渍法制备负载型催化剂HSiW/MCM-48。以XRD、N_2吸附-脱附、NH_3-TPD对样品进行表征,以油酸的酯化反应为探针测试样品的催化性能,并考察了HSiW负载量对催化剂结构和性能的影响。研究结果表明:HSiW/MCM-48催化剂保持MCM-48的三维立方相介孔结构,但随HSiW负载量增加,HSiW/MCM-48催化剂介孔的长程有序性逐渐下降,比表面积和孔容同时减小;催化剂在油酸的酯化反应中呈现出良好的催化性能;当HSiW负载量达20%时,催化活性较高,油酸甲酯的收率高达80.5%。     

Oxovanadium(IV) salicylidene Schiff base complex anchored on mesoporous silica MCM-41 as hybrid materials: a robust catalyst for the oxidation of sulfides

Oxovanadium(IV) Schiff base complex have been anchored onto the surface of purely siliceous MCM-41 and tested for its activity as catalyst for the oxidation of sulfides. This catalyst could alter this oxidation reaction extremity, exhibiting excellent yields with 100 % selectivity. The intercalation of the complex inside the silica matrix was supported by various characterization techniques like X-ray diffraction, differential thermogravimetric (TG-DTA), BET measurements, UV–Vis diffuse reflectance spectroscopy and Fourier transform infrared spectroscopy (FT-IR). The stability of the catalyst during the course of the reaction was confirmed from its post catalytic FT-IR and XRD analysis. The catalyst could be reused five times without notable loss of its catalytic activity and efficiency which indicates that the metal-Schiff base moiety is intact and the coordination environments are not altered during the reaction.     

Characterization and catalytic properties of MCM-56 and MCM-22 zeolites

We present an investigation of the structure and properties of MCM-56 and MCM-22. These materials have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N₂ adsorption isotherms. DIFFaX was used to simulate pronounced peak broadening in the X-ray diffraction patterns of MCM-56. Toluene disproportionation is used as a test reaction to compare the catalytic activity of MCM-22 and MCM-56. We have found that MCM-56 is made of very thin MWW-type layers. The layers are typically one unit cell along the c direction (with a few of them having two or three unit cells). These very thin layers of MCM-56 become tightly curled upon calcination. The structures thus formed pack very efficiently, and this phenomenon prevents access of organic molecules like toluene to most of the 12 MR cups on the crystal exterior. Although MCM-56 is active for the disproportionation of toluene, its activity is lower than that of MCM-22. A calcination procedure that prevents the curling up of the MCM-56 layers is needed to make MCM-56 a useful catalyst for large organic molecules.     

Preparation of mesoporous MCM-41 from natural sepiolite and its catalytic activity of cracking waste polystyrene plastics

Mesoporous MCM-41 was prepared by leaching of sepiolite and sequent hydrothermal synthesis in NaOH solution with hexadecyltrimethylammonium bromide as template. Small-angle X-ray diffraction patterns, Scanning electron microscopy, transmission electron microscopy and Brunauer–Emmett–Teller were performed to characterize the resulting compounds. The results showed that the crystallinity and pore size of MCM-41 increased with increase of crystallization time, ratios of surfactant to SiO₂ and decrease of Mg content. The experimental results of catalytic cracking of polystyrene waste showed that the MCM-41 with MgO from natural sepiolite had high catalytic activity and good selectivity to monomer styrene for the catalytic cracking of polystyrene when the ratio of waste plastics to MCM-41 was 200. The side reactions yielded ethylbenzene, isopropylbenzene, isopropenylbenzene and secondary cross-linking were suppressed by basic species MgO in MCM-41.     

MCM-48介孔分子筛合成和改性研究进展

MCM-48介孔分子筛因具备高度有序的孔道,较大的比表面积,可控的形貌,良好的催化性能及优异的传质与扩散效率等优势成为化学工业、信息技术和环境能源等领域的研究热点.整理了MCM-48介孔分子筛的合成方法,主要包括水热合成法、微波合成法、室温合成法、相转变合成法,概述了不同的合成原料(如硅源、模板剂)和合成条件(如pH值...     

The entrapment of UO2 in mesoporous MCM-41 and MCM-48 molecular sieves

A method based on direct template-ion-exchange was employed for the entrapment of UO₂²⁺ ions in MCM-41 and MCM-48 molecular sieves via swapping of cetyltrimethylammonium cations present in the mesoporous channels by the UO₂²⁺ ions in an aqueous solution. The samples were characterized by XRD, FT-IR, and ICP-AES techniques. The entrapment of UO₂²⁺ ions is facilitated by the large pore size vis-a-vis the high surfactant content in the as-synthesized host materials. A higher loading of UO₂²⁺ ions was achieved in MCM-48 as compared to MCM-41, which could be attributed to its three-dimensional pore system and higher surfactant-to-silica ratio. FT-IR results provide an evidence of a strong binding of UO₂²⁺ groups with the defect silica sites of mesoporous molecular sieves.     

含氟体系中合成条件对MCM-48分子筛结构性能的影响

在合成过程中引入F~-可以缩短MCM-48分子筛的晶化时间,考察以正硅酸乙酯(TEOS)为硅源、十二烷基三甲基溴化铵(CTAB)为模板剂的合成体系中加入F~-后,n(CTAB)∶n(Si)、晶化时间和晶化温度等合成条件对MCM-48结构性能的影响。XRD、N_2吸附脱附和TEM等表征结果表明,在n(CTAB)∶n(Si)=0.65、晶化温度120℃和反应时间24 h条件下,合成的MCM-48分子筛结晶度较高,比表面积为1 305 m~2·g~(-1),平均孔径3.416 nm,为MCM-48分子筛的适宜合成条件。     

锐钛型介孔偏钛酸催化剂的制备及其催化酯化性能

以工业偏钛浆为原料,通过水洗、碱洗、酸洗处理制备了锐钛型介孔偏钛酸催化剂,将催化剂用于α-蒎烯酯化反应中考察其催化性能,采用FT-IR、XRD、SEM、BET手段对催化剂的晶相结构、形貌、表面积、孔径等结构进行了表征。结果表明,最佳制备条件为：温度30 ℃,碱洗pH=8.5,酸洗pH=4.0;处理后的偏钛酸催化剂基本没有SO42?,且晶型没有发生明显变化,均为锐钛矿相,最佳条件下制备的偏钛酸催化剂孔径分布均匀,晶粒团聚较少,比表面积为334.82 m2/g,平均孔径为3.96 nm,催化α-蒎烯酯化生成草酸龙脑酯含量可达48.59 %,皂化后水蒸气蒸馏收集龙脑,m1（正龙脑）∶m2（异龙脑）=59.27∶37.07。     

Synthesis and characterization of tungsten-incorporated mesoporous molecular sieve MCM-48 by one step

Tungsten-substituted mesoporous MCM-48 materials are successfully synthesized at 393 K by a one-step co-condensation sol–gel method. The prepared samples with different Si/W ratios are characterized by X-ray diffraction (XRD), nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), diffuse reflectance UV–visible spectroscopy and FT-IR, and the results indicate the presence and good dispersion of tungsten species inside the silica pores, the Si/W ratio is controlled above 28. When the Si/W ratio is less than 28, though no bulk tungsten is detected outside the MCM-48 mesoporous silica, the pore structure order becomes worse.     

Room temperature blue-green photoluminescence of MCM-41, MCM-48 and SBA-15 mesoporous silicas in different conditions

The photoluminescence (PL) properties of siliceous MCM (MCM-41 and MCM-48) and SBA-15, no Na-containing MCM-41, and modified SBA-15 by silylation were comparatively investigated in dry and damp conditions, displaying the highest PL intensity of MCM-48. The PL intensity of MCM-41 is lower than that of SBA-15 in dry conditions, but reverse in damp conditions. In comparison with that of Na-containing MCM-41, the PL intensity of MCM-41 without Na⁺ is stronger. The PL intensity of modified SBA-15 by silylation is decreased in dry conditions, and however, against moisture and degradation in damp conditions. Twofold coordinated silicon centers in the tested samples are responsible for the blue-green bands at 440 nm. The shoulder peaks around 460–490 nm occurred in damp conditions are assigned to peroxy free radicals.     

Fe(III)-salim anchored MCM-41: synthesis,characterization and catalytic activity towards liquid phase cyclohexane oxidation

Abstract  

A novel organic–inorganic hybrid catalyst [MCM-41-Fe^III(salim)] was synthesized by covalently anchoring Fe^III(salim) complex into the pore channels of MCM-41. The material was synthesized by the co-condensation of tetraethyl orthosilicate (TEOS) and the precursor of salicylaldehyde modified with 3-aminopropyl triethoxysilane in the presence of cetyltrimethyl ammonium bromide (CTAB). The Fe(III)-salicylideneimine MCM-41 mesoporous silica was generated (in situ) by taking MCM-41-salimH (I) and FeCl₃ in ethanol solution. The immobilization of the complex on the functionalized silica was confirmed by small angle X-ray diffraction (XRD), N₂ adsorption–desorption, electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FT-IR) and diffuse reflectance UV–vis spectroscopy. Solid state CP-MAS NMR spectroscopy of ²⁹Si (²⁹Si CP-MAS NMR) showed a highly condensed siloxane network. Catalytic activity of the supported catalyst was examined by the oxidation of cyclohexane. Cyclohexane was successfully oxidized in good conversion (68%) to cyclohexanone, as a major product with 72% selectivity using tert. butylhydroperoxide as oxidant and acetonitrile as solvent. The catalysts can be reused up to three cycles without losing much of its activity.     

Facile Suzuki coupling over ortho-metalated palladium(II) complex anchored on 2D-hexagonal mesoporous organosilica

Phenyl functionalized 2D-hexagonal mesoporous silica material has been synthesized by cationic/non-ionic mixed surfactant templating route. The phenyl group of this mesoporous material is further functionalized via nitration and then reduction of that nitro group to amino functionality, followed by Schiff base condensation and heterogenization of a palladium(II) complex, yielded an ortho-metalated palladium(II) complex anchored in a ordered mesoporous silica matrix. This supported metal complex acts as an efficient catalyst in the Suzuki cross-coupling reaction and shows high selectivity for the bi-aryl products.     

Acidity and catalytic activity of the mesoporous aluminosilicate molecular sieve MCM-41

The acidity and catalytic properties of aluminosilicate mesoporous molecular sieves with the MCM-41 structure and bulk Si/Al ratios in the 10–60 range have been investigated. The incorporation of 4-coordinate aluminium into the structure of MCM-41 generates both BrØnsted and Lewis acid sites in amounts increasing with the degree of incorporation. However, the BrØnsted/Lewis acid population ratio is independent of the content of aluminium. The number and strength of acid sites generated are comparable to those of a pillared acid-activated clay and lower than in zeolite H-Y with Si/Al=3.65. Aluminosilicate MCM-41 is a moderate catalyst for the conversion of cumene which proceeds predominantly via catalytic cracking to propene and benzene. The sample of MCM-41 with the highest content of framework aluminium (Si/Al=10) has the largest number of BrØnsted acid sites and exhibits highest catalytic activity.