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.     

Preparation and characterization of Pd/Si-MCM-41 with high hydrogenation activity

The pure silica mesoporous molecular sieve MCM-41 was synthesized under hydrothermal conditions. Pd/Si-MCM-41 was prepared by the incipient wetness impregnation of pure silica MCM-41 with PdCl₂ as precursor. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption–desorption isotherms at 77 K, inductively coupled plasma (ICP) spectroscopy measurements. The formation of Pd particles reduced the crystalline character of Si-MCM-41, but the structure of Si-MCM-41 framework was retained. The designed Pd/Si-MCM-41 mesoporous material was used as catalysts for hydrogenation of rosin, and showed excellent catalytic performance. Such outstanding catalytic performance should be attributed to the proper size of Pd particles and its high dispersion.     

Characteristics of Gallium-Substituted Hexagonal Mesoporous Silica: Effects of Gallium Content

Gallium-substituted hexagonal mesoporous silicas (Ga-HMS) with various Si/Ga ratios in the range of 15 and 200 were prepared at ambient temperature by neutral surfanctant templating pathway. The materials were synthesized by using dodecylamine as a template and tetraethylorthosilicate as a silicon source. They were characterized by energy dispersive X-ray spectroscopy, powder X-ray diffraction (XRD), N₂ adsorption-desorption, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared absorption spectroscopy and ultraviolet-visible absorption spectroscopy. Ga-HMS samples had high surface areas and uniform mesoporous channels, which are similar to MCM-41. However, they differed from MCM-41 in presenting only a single peak in XRD patterns. They also possessed other characters of larger framework wall thickness, small crystallite domain sizes, and complementary textural mesoporosities in comparison with M41S materials. Ga-HMS materials had micropores and the hysteresis loops were obvious. These small crystallite size and complementary textural mesoporosity provided better access of the framework-confined mesopores. These mesoporous Ga-HMS samples exhibited irregularly shaped mesoscale fundamental particles which aggregated into larger particles. They also demonstrated better thermal stability than MCM-41. The textural pore volumes of Ga-HMS specimens could be up to 20 times as large as the framework volumes. The surfactant could be removed completely by calcination at 650^∘C. An absorption band of FT-IR at ca. 960 cm^–1 was assigned to the vibration of Si–O–Ga linkages. These samples also showed an absorbance band at 255 nm and 250 nm in UV-vis spectra. The results show that gallium was incorporated into the structure of HMS. The efforts in preparing Ga-HMS specimens by neutral-template synthesis route had led to new mesoporous silica molecular sieves with catalytically active gallium centers.     

Effects of surfactant/silica and silica/cerium ratios on the characteristics of mesoporous Ce-MCM-41

Using the surfactant CTMABr (cetyltrimethyl ammonium bromide) and cerium(IV) sulfate, mesoporous Ce-MCM-41 molecular sieves were produced under a hydrothermal condition with various surfactant/silica (surfactant/Si) and silica/cerium (Si/Ce) ratios. Changes to the structural traits caused by changing the molar ratios of both surfactant/Si and Si/Ce were investigated. XRD (X-ray diffraction), FT-IR (fourier transform infrared spectroscopy), and SEM (scanning electro microscopy) were used for the characterization of prepared mesoporous samples. Among the tested molar ratios, surfactant/Si ratio of 0.5 and 0.2 showed highest values of d_1 0 0 and intensity, respectively, for the Si-MCM-41. XRD analysis also identified a quintessential hexagonal structure of Ce-MCM-41 for the Si/Ce molar ratio higher than 40 (maintaining the surfactant/Si ratio at 0.2). When cerium content was increased to have the Si/Ce molar ratio of 20, the hexagonal structure of Ce-MCM-41 was collapsed due to the structural stress of substituted cerium. FT-IR results confirmed calcination of Ce-MCM-41 and the incorporation of Ce⁴⁺ ions of cerium sulfate into the silica surface with proper removal of the surfactant. Rod-like shape with rounded edges of the prepared Ce-MCM-41 samples was identified by SEM. These results suggest surfactant/Si ratio of 0.2 and Si/Ce ratio of 40 for the production of Ce-MCM-41 with the highest level of crystallinity.     

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.     

Synthesis and characterisation by X-ray absorption spectroscopy of a suite of seven mesoporous catalysts containing metal ions in framework sites

MCM-41 type mesoporous silicas have been prepared in which one or more of the following elements are accommodated in framework sites: titanium, iron, chromium, vanadium, manganese, boron and aluminium. XRD and FTIR are used as aids to characterisation, which is achieved chiefly — and to a degree that arrives at valence states, bond lengths and coordination numbers of the metal ion — by X-ray absorption spectroscopy (XAS). Ti-containing MCM-41, as well as the Fe-, V- and Cr-containing variants, yield self-consistent, XAS-based, structural data of the respective metal-ion sites. Some of these (especially those containing Ti) are exceptionally good catalysts for the selective oxidation of large organic molecules such as limonene and norbornene.     

Covalent grafting of polyacrylamide onto mesoporous MCM-41 silica via free radical polymerization

MCM-41 mesoporous silicas were covalently modified with polyacrylamide (PAAm) by a novel grafting strategy. The effect of various parameters such as monomer concentration, reaction time, and temperature on the content of PAAm onto MCM-41 silicas were studied. Modified silicas were characterized by X-ray diffraction (XRD), infrared spectroscopy, FT-IR, thermogravimetric analysis, nitrogen adsorption–desorption analyses, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy which confirmed the grafting process. According to XRD, SEM and TEM results, PAAm-modified MCM-41 silica did not show changes in its morphology and mesostructure by comparing with pristine MCM-41. Nitrogen adsorption–desorption studies showed that the attaching of PAAm onto MCM-41 silica decreased the values of pore size, pore volume and surface area.     

Phase transition of mesoporous SiO<Subscript>2</Subscript> impregnated with an organic templating agent by post-synthetic microwave heating

Mesoporous silica SBA-15 samples were subjected to microwave heating for 10–40 min at 393 and 443 K after dry-impregnation with TPAOH (tetrapropylammonium hydroxide) to prepare a mesoporous material with zeolytically ordered pore walls. Physicochemical properties of the materials prepared were characterized by XRD, N₂ adsorption at 77 K, SEM, TEM, UV–vis and FT-IR spectroscopies. These investigations revealed that selective transformation of amorphous pore walls of SBA-15 to crystalline zeolytic phase is difficult to be achieved and a mixed phase of mesoporous silica/zeolite composite material was obtained, instead. Microwave heating time, temperature, TPAOH concentration, and hydrothermal stability of the mesoporous host materials tested (MCM-41, HMS, and SBA-15) were important factors to maintain the mesopore structure of the host materials during the post-synthetic microwave heating treatment.     

Effect of pH in hydrothermal treatment of as-synthesized MCM-41 on wetting stability of resulting materials in aqueous solution

Effect of pH in aqueous media used in the hydrothermal treatment of as-synthesized MCM-41 on the structure and the wetting stability of the resulting materials was studied using XRD, TG-DTA and N₂ adsorption. The long-range structural order and the wetting stability of the mesoporous MCM-41 were improved through hydrothermal treatment of as-synthesized sample at around pH 7 without salt addition. The pH adjustment of aqueous media toward neutral is thought to shift the polymerization equilibrium of silica species around external surface of the micelles to a higher degree of condensation, and to reduce the electrostatic repulsion between the silicate–micelle composites. This leads to the further formation of Si–O–Si network within the silica walls of the mesoporous materials, resulting in the enhancement of the structural stability of MCM-41 samples.     

An organic/inorganic hybrid mesoporous silica membrane: preparation and characterization

An organic/inorganic hybrid mesoporous silica membrane composed of mesoporous silica materials inside the channels of polycarbonate filtration membrane (PC) was synthesized by using aspiration-induced infiltration method, and the surfactant in as-prepared membrane was removed by employing template-extraction method. The obtained materials were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD),transmission electron microscopy (TEM) and N₂ adsorption–desorption measurement. The SEM images and EDS elemental analyses show that as-synthesized materials in PC are one-dimensional silica rods estimated as 200 nm in diameter and 9 μm in length. Moreover, the results of XRD, TEM and N₂ adsorption–desorption analysis clearly demonstrate that such silica rods are mesoporous materials with two-dimensional hexagonal mesostructure and the average mesopore diameter is about 3.0 nm. In addition, the porosity of organic/inorganic hybrid mesoporous silica membrane was further examined by molecule permeation. It is found that small molecule, such as rhodamine B, can transport across the membrane, but relatively large molecule, such as horse radish peroxidase, can not transport across the membrane, indicating that it is size-selectivity of such a membrane for molecule permeation, which has the potential application in the molecule filters to separate bio-macromolecule from small molecule.     

Mesoporous silica MCM-41 with rod-shaped morphology: Synthesis and characterization

A new synthesis route has been established to prepare highly pure mesoporous silica material (Si-MCM-41) with rod-like morphology. To improve the stability and to bring about the long range ordering in the mesoporous material, a series of tetra-alkylammonium salts has been employed in the new procedure in addition to the surfactant, cetyl-trimethylammonium bromide. The mesoporous silica materials have been characterized by small-angle X-ray diffraction (SAX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ sorption and solid state ²⁹Si NMR measurements. The XRD study revealed that an excellent long range structural ordering of mesoporous material can be achieved using tetra-butylammonium bromide as a promoter. SEM study showed that rod-shaped single crystal like particles were formed in hydrothermal synthesis. TEM study revealed the presence of hexagonal voids on the face of the rod-shaped particles while nitrogen sorption study establishes the mesoporosity of the material. A high degree of cross-linking of -Si-O-Si- networks in the mesoporous silica has been evidenced in ²⁹Si NMR study.     

Synthesis of macroporous ZrO2–Al2O3 mixed oxides with mesoporous walls, using polystyrene spheres as template

Macroporous ZrO₂–Al₂O₃ mixed oxides with mesoporous walls were synthesized. The three-dimensional interconnected macroporous structures, of inorganic zirconia–alumina mixed oxides containing different alumina compositions (25, 50, 100 wt%), were prepared by sol–gel method from inorganic precursors and using polystyrene microspheres with diameters of 685 and 1520 nm as templates. The final porous arrays with controllable pore size in the submicrometer range could be obtained by calcination of the organic template. The structural characteristics are discussed. The physicochemical characterization of the samples was carried out by N₂ physisorption (S_BET), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The shrinkage of pore diameter was approximately 35%, and the wall thickness of inorganic framework varied between 135 and 154 nm. The specific surface areas, of the samples, were between 123 and 287 m²/g, obtaining the largest surface area with the highest alumina contents and the smallest templates.     

Synthesis of chloropropylamine grafted mesoporous MCM-41, MCM-48 and SBA-15 from rice husk ash: their application to CO<Subscript>2</Subscript> chemisorption

Mesoporous siliceous MCM-41, MCM-48 and SBA-15 were synthesized using Rice Husk Ash (RHA) as the silica source. Their defective –OH sites were then grafted with 3-chloropropyl amine hydrochloride (3-CPA) and characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and BET techniques. Those results portrayed their resemblance with that synthesized from conventional silica sources. 3-CPA grafted mesoporous silicas were tested for CO₂ chemisorption over fixed bed reactor at different temperatures. The maximum adsorption of 1.7 mmol/g of CO₂ was observed on 3-CPA grafted SBA-15 (SBA-15/CPA) at 25°C. The chemisorbed CO₂ on amine grafted mesoporous silica was stabilized by weak hydrogen bonds formed during the nucleophilic attack between lone pair of electrons in amine groups and quadrupolar CO₂ with more degree of positive charge to form carbamates. The rapid steep slope which arises due to CO₂ adsorption illustrated a minimal mass transfer effect and extreme fast kinetics. Performance tests such as reproducibility, stability and selectivity towards CO₂ adsorption were also carried out over 3-CPA grafted mesoporous silica and the results were in line with that of well established CO₂ sorbent.     

Production of biodiesel by esterification of palmitic acid over mesoporous aluminosilicate Al-MCM-41

Biodiesel has been obtained by esterification of palmitic acid with methanol, ethanol and isopropanol in the presence of Al-MCM-41 mesoporous molecular sieves with Si/Al ratios of 8, 16 and 32. The catalytic acids were synthesized at room temperature and characterized by atomic absorption spectrometry (AAS), thermal analysis (TG/DTA), X-ray diffraction (XRD), nitrogen absorption (BET/BJH), infrared spectroscopy (IR), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The reaction was carried out at 130 °C whilst stirring at 500 rpm, with an alcohol/acid molar ratio of 60 and 0.6 wt% catalyst for 2 h. The alcohol reactivity follows the order methanol > ethanol > isopropanol. The catalyst Al-MCM-41 with ratio Si/Al = 8 produced the largest conversion values for the alcohols studied. The data followed a rather satisfactory approximation to first-order kinetics.     

Ordered mesoporous sulfated silica-zirconia materials with high zirconium contents in the structure

A series of mesoporous sulfated silica-zirconia materials with various Si/Zr molar ratios (2.0–5.0) have been prepared using tri-block copolymer as a template, which were characterized by X-ray diffraction, TEM, nitrogen adsorption, UV-Vis diffuse reflectance spectroscopy, infrared spectroscopy, thermal gravimetric analysis, and catalytic reactions. XRD patterns displayed that ordered mesoporous sulfated silica-zirconia materials were obtained when the molar ratio of Si/Zr was not less than 4.0 (ZrSiS-4 and ZrSiS-5). When the molar ratio of Si/Zr was less than 4.0, the samples had a separated phase of amorphous sulfated zirconia (ZrSiS-2 and ZrSiS-3). Furthermore, TEM images (ZrSiS-4 and ZrSiS-5) revealed that the mesostructure of these materials were highly ordered. N₂ adsorption (ZrSiS-4 and ZrSiS-5) exhibited typical IV adsorption isotherms and uniform pore distribution. UV-Vis reflectance and IR spectra suggested (ZrSiS-4 and ZrSiS-5) that Zr atoms were incorporated into the walls of mesoporous silica. Cracking reactions of cumene and 1,3,5-triisopropylbenzene (TIPB) showed that, the ordered mesoporous sulfated silica-zirconia materials were very active in acidic catalytic reactions, especially for the cracking of large molecules.     

Metal (Co,Mn)-amine-functionalized mesoporous silica SBA-15: synthesis,characterization and catalytic properties in hydroxylation of benzene

Mesoporous silica SBA-15 was synthesized using H₃PO₄ and functionalized with ethylendiaminopropyltrimethoxysilane (H₂N–(CH₂)₂–NH–(CH₂)₃–) by grafting method. A variety of transition metals such as Co and Mn have been coordinated with amine-functionalized silica SBA-15. The materials have been characterized by XRD, FT-IR, BET, TGA, ¹³C-NMR, DR UV–Vis, atomic absorption spectroscopy (AAS) and back titration using NaOH (0.1 N). The catalytic performance of obtained catalyst was determined for hydroxylation of benzene using H₂O₂ as oxidant in the presence of O₂ atmosphere. At optimized conditions, the Mn-amine-functionlized mesoporous silica SBA-15 exhibited high catalytic activity at room temperature in the absence of solvent.     

含Bi中孔分子筛(Ⅰ)合成和表征与催化性能

以十六烷基三甲基溴化铵为模板剂,正硅酸乙酯为硅源,硝酸铋为铋源,在弱碱性条件下用水热法合成了具有Mobile Crystalline Material-41结构的Bi-Si中孔分子筛,通过XRD、N₂吸附等温线、TG、SEM、FT-IR、UV-Vis等多种表征手段对其进行结构、性质分析,结果表明：所合成的分子筛具有良好的长程有序结构和孔结构,并且铋高度分散于分子筛骨架中.在苯乙烯催化氧化制苯甲醛中有很好的催化活性,当Si/Bi＝22.5（摩尔比）,反应时间为1 h,反应温度为80 ℃时苯甲醛的产率达到14.1％.考察了分子筛有序度与铋含量及改性金属对催化活性的影响.     

Synthesis of mesoporous Si/SiC with three-dimensional structure derived from C/silicalite-1 via magnesiothermic reduction

C/silicalite-1 composites were successfully synthesized by using industrial silica sol as silica source and multiwalled carbon nanotube (MWCNTs) as carbon source under hydrothermal method. Then, C/silicalite-1 composites were transformed into mesoporous Si/SiC through magnesiothermal reduction at relatively low temperature (650 °C). The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and Brunauer–Emmett–Teller analysis (BET). The XRD patterns and TEM micrographs exhibit that C/silicalite-1 composites are transformed into Si/SiC. The SEM images exhibit that Si/SiC keeps the three-dimensional structure of silicalite-1. BET analysis shows that the specific surface areas and mesoporous distribution of Si/SiC are 274 m²/g and 4.69 nm, respectively.     

Pd/Ce-HMS介孔材料的结构和表面化学态

为了制备新型负载型Pd催化剂,采用合成后组装法和浸渍法室温合成了Pd/Ce-HMS介孔材料,产物用XRD、N2吸附、FTIR及XPS谱等手段进行表征。结果表明,Ce、Pd引入后六方介孔结构仍保持完好。产物的BET表面积为742.9 m2·g-1,孔容0.803 cm3·g-1,表面Pd、Ce物种主要以PdO2和CeO2形式存在。研究表明,Ce前驱体通过与孔表面富集的Si—OH基团作用而嵌入骨架或键合于孔表面,Pd担载时由于模板剂仍留在孔道中,因而没有造成孔道堵塞。     

Synthesis and characterization of mesoporous molecular sieve nanoparticles

Mesoporous molecular sieve was prepared hydrothermally by a two-step method with materials of cetyltrimethyl ammonium bromide (CTAB), as a template, and sodium metaaluminate (NaAlO₂) and sodium silicate (Na₂SiO₃·9H₂O), as aluminum and silicon sources, respectively. The mesoporous molecular sieves are well ordered and have high thermal and hydrothermal stabilities. The as-prepared samples were characterized by powder X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), thermogravimetry-differential scanning calorimetry (TG/DSC), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption experiments. Particle size distribution was in the 30–50 nm range, BET surface area was more than 800 m²/g, thermal stability was higher than 1023 K, the mesoporous structure was not entirely damaged at a calcination temperature of 1123 K and there was no clear change in ordering degree, pore size, and surface area of the mesoporous molecular sieve after hydrothermal treatment at 373 K for 10 days. The activity and selectivity of benzene hydrogenation to cyclohexane by mesoporous molecular sieve-supported Pt was up to 100%. The catalytic activity didn’t decline in a reaction period of 30 h.