Effects of fluoride ion on the formation of earthworm‐like mesoporous silica

In a strong acidic environment, ordered earthworm‐like mesoporous silica has been synthesized with CTAB templating and fluoride ion (F^?) as a counterion. The synthesized products were characterized by small‐angle X‐ray diffraction (SXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption‐desorption isotherms, and Fourier‐transform infrared spectroscopy (FTIR). The effects of F/Si mole ratio on the morphology, surface area, and the pore size of the sample were discussed. It was found that a F/Si mole ratio at 0.083 induced the formation of 3D hexagonal mesophase, whereas higher F/Si mole ratios led to the formation of 2D hexagonal mesoporous silica, the optimum molar ratio of F/Si for the formation of delicate earthworm‐like mesoporous silica was observed at 0.250. The effects of the F/Si mole ratio, surfactant chain length, acid concentration, and shear flow on morphology were also studied.     

Characterization and synthesis of Ce-incorporated mesoporous molecular sieves under microwave irradiation condition

Ce-incorporated MCM-41 mesoporous molecular sieves (CeMCM-41) were synthesized by microwave irradiation method from sodium silicate and ammonium cerium (IV) nitrate precursors and using cetyltrimethyl ammonium bromide (CTAB) as template. The resulting samples were characterized by means of XRD, TEM, FT-IR, UV-Vis, XPS and N₂ physical adsorption, respectively. The effect of the Si/Ce molar ratio on the textural properties of CeMCM-41 was investigated. The results reveal that the CeMCM-41 was successfully synthesized. The resultant mesoporous materials have specific surface areas in the range of 602–1,216 m²/g and pore sizes in the range of ca. 2.6–2.9 nm. The structural properties are related to the amount of cerium incorporation. The surface area and pore volume of the resulting CeMCM-41 were gradually reduced as the cerium content in the sample increased, and the mesoporous ordering diminished.     

Direct synthesis of CeO2/SiO2 mesostructured composite materials via sol–gel process

A series of CeO₂/SiO₂ mesostructured composite materials was synthesized by sol–gel process using Pluronic P123 as template, tetraethylorthosilicate as silica source and hexahydrated cerium nitrate as precursor under acid condition. The as-synthesized materials with Ce/Si molar ratio ranging from 0.03 to 0.3 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), laser Raman spectroscopy (LRS), and N₂ adsorption. Characterization revealed that all samples possess ordered hexagonal mesoporous structure similar to SBA-15 and possess high surface area, large pore volume and uniform pore size. The fact that cerium species are present as highly dispersed CeO₂ nanocrystals in hexagonal matrix was confirmed by XRD combined with high-resolution TEM and selected area electron diffraction (SAED) analysis. Introduction of ceria to silica matrix can cause a distortion of hexagonal ordering structure and decrease pore diameter and increase the wall thickness of mesopores. Moreover, it can be found that this sol–gel route is a feasible, effective and simple method for templating synthesis of CeO₂/SiO₂ composite materials.     

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。     

Characteristics of vanadium-substituted mesoporous silica with wormhole framework structure: effects of vanadium content

Vanadium-substituted wormhole framework structure (V-WMS) mesoporous silicas (V-WMS) with various Si/V ratios in the range of 15 and 200 were prepared at ambient temperature by neutral surfactant 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 (EDS), powder X-ray diffraction (XRD), N₂ adsorption–desorption, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared absorption spectroscopy (FT-IR) and ultraviolet-visible absorption spectroscopy. V-WMS samples shown characters of larger framework wall thickness, small crystallite domain sizes, and complementary textural mesoporosities in comparison with M41S materials. These mesoporous V-WMS samples exhibited irregularly shaped mesoscale fundamental particles which aggregated into larger particles. They also demonstrated better thermal stability than MCM-41. An absorption band of FT-IR at ca. 960 cm⁻¹ was assigned to the vibration of Si–O–V linkages. These samples also showed one strong UV–visible absorbance with overlapping maxima at about 255 nm. The results show that vanadium was incorporated into the structure of wormhole mesoporous silica (WMS). However, for V-WMS with high vanadium content (Si/V < 25), a broad shoulder in XRD pattern was observed at about 3–4°, suggesting the presence of impurity phase of vanadium species in the sample. The efforts in preparing V-WMS specimens by neutral-template synthesis route had led to new mesoporous silica molecular sieves with catalytically active vanadium centers.     

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.     

Novel synthesis of ordered mesoporous materials Al-MCM-41 from bentonite

This paper reports the synthesis of ordered mesoporous materials Al-MCM-41 with a specific surface area of 1018 m²/g from bentonite. Pretreated bentonite was simultaneously used as silica and aluminum sources without addition of silica or aluminum reagents. Orthogonal experiments were adopted to optimize the processing parameters. The samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N₂ adsorption–desorption measurements and Fourier transform infrared spectra (FTIR) techniques. The obtained materials were hexagonal Al-MCM-41. Calcination removed the surfactant while new bonds increased the crosslinking of the frameworks. Proper Si/Al molar ratio was critical for the formation of highly ordered mesoporous materials.     

Synthesis of dypnone using SO4/Al-MCM-41 mesoporous molecular sieves

The mesoporous molecular sieves Al-MCM-41 with Si/Al ratio equal to 16, was synthesized under hydrothermal conditions using cetyltrimethylammonium bromide (CTMA⁺Br⁻) as surfactant. The same ratio of Al-MCM-41 materials was impregnated using sulfuric acid, the materials as sulfated Al-MCM-41 (SO₄²⁻/Al-MCM-41). The mesoporous materials viz Al-MCM-41 and SO₄²⁻/Al-MCM-41 were characterized using several techniques e.g. ICP-AES, Nephelometer, XRD, FT-IR, TG/DTA, N₂-adsorption, solid-state-NMR, SEM and TPD-pyridine. ICP-AES studies indicated the presence of Al in the mesoporous materials. Nephelometer studies indicated the SO₄²⁻ presence of the SO₄²⁻/Al-MCM-41. XRD studies indicated that the calcined materials of Al-MCM-41 and SO₄²⁻/Al-MCM-41 had the standard MCM-41 structure. The surface area, pore diameter, pore volume and wall thickness of the mesoporous materials were calculated by BET and BJH equations, respectively. Crystallinity, surface area, pore diameter and pore volume of SO₄²⁻/Al-MCM-41 decreased except wall thickness and the expelling aluminum from the Al-MCM-41 framework increased the Lewis acidity. FT-IR studies indicated that Al-ions were incorporated in the hexagonal mesoporous structure of Al-MCM-41 and sulfuric acid was impregnated into hexagonal Al-MCM-41 materials. The thermal stability of as-synthesized Al-MCM-41 materials and SO₄²⁻/Al-MCM-41 materials were studied using TG/DTA. The environments of the Al-ions coordinated in the silica matrix were determined by ²⁷Al-MAS-NMR. The morphology of Al-MCM-41 and SO₄²⁻/Al-MCM-41 was determined by SEM. The total acidity of Al-MCM-41 and SO₄²⁻/Al-MCM-41 materials was determined by TPD-pyridine. The catalytic results were compared with those obtained by using sulfuric acid, amorphous silica–alumina, H-β, USY and H-ZSM-5 zeolites. The SO₄²⁻/Al-MCM-41 catalyst exclusively forms the product of dypnone from self-condensation of acetophenone molecules due to higher number of Lewis acid sites and has much higher yields than other catalysts except USY.     

Synthesis of mesoporous silica with cationic-anionic surfactants

Ordered mesoporous silica was successfully synthesized by using mixed surfactants, cetyltrimethylammonium bromide and sodium dodecylsulfate, proceeded with the hydrolysis and condensation of tetraethyl orthosilicate in a mixture of TritonX-100 as a cosolvent. The synthesized products were characterized by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen sorption analysis. It was found with increasing the anionic surfactant sodium dodecylsulfate to cetyltrimethylammonium bromide molar ratio, the morphologies of mesoporous silica changed from spherical shape to ellipsoidal shape, at last became rod-like and lamellar shape. Correspondingly the pore diameter and surface area of mesoporous silica all decreased according to nitrogen sorption analysis. The TEM analysis illustrated the product with ordered hexagon mesostructure and homogeneous pore arranged can be obtained, when the molar ratio of cetyltrimethylammonium bromide/sodium dodecylsulfate is 15: 1. It also demonstrated the less the molar ratio of sodium dodecylsulfate was used, the more ordered pore structure the products exhibited. Furthermore, prolonging the crystal time was beneficial to improve the stability of the product.     

An Easy Route to Synthesize Novel Mesostructured Silicas Al/SBA-16 and Its Catalytic Application

Abstract  

Al-containing SBA-16 (with different Si/Al molar ratios) was prepared by an easy post-grafting method using F127 as structure-directing agent and aluminum isopropoxide as Al source. The structure of the solid catalyst was fully characterized by X-ray diffraction (XRD) analysis, N₂ adsorption, scanning electron micrographs (SEM), transmission electron micrographs (TEM) and ²⁷Al MAS NMR. The results indicated that the materials possess three-dimension caged-like mesostructure and Al was successfully incorporated into the SBA-16 framework. The acid properties have been estimated by FT-IR of pyridine adsorption (Py-IR). Among various Si/Al ratios, Al/SBA-16 with Si/Al ratio 20 performed good catalytic activity for the tert-butylation of phenol. Compared to hexagonal mesoporous Al/SBA-15, Al/SBA-16 showed higher catalytic properties due to its cage-like mesostructure, which could make the active acid sites more accessible to the reactant.     

Low-temperature ozone decomposition,CO and iso-propanol combustion on silver supported MCM-41 and silica

Silver modified (5 and 2 wt% loading) mesoporous molecular sieves (H-MCM-41, with Si/Al ratio 20, 40 and 50) and silica were synthesized by incipient wetness impregnation and ion-exchange methods. The obtained catalysts were characterized by different techniques (ICP, XRD, XRF, SEM, FTIR and nitrogen physisorption) and they were tested in heterogeneous catalytic decomposition of ozone and oxidation reactions involving ozone at ambient temperature. All the mesoporous catalysts have very high catalytic activities towards ozone decomposition at room temperature and they do not reveal any deactivation with the time on stream. The activities of the catalysts are enhanced upon increasing the amount of supported silver, decreasing the support acidity and modifying the catalyst with some additional metal having basic properties, such as Ce. The most active catalyst in the reaction of ozone decomposition—5Ag-H-MCM-41-50, shows also high activity at ambient temperature in the oxidation of CO and iso-propanol with ozone.     

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.     

Highly dispersed zinc phosphate microdomains in mesoporous silica

In situ immobilization of crystalline zinc phosphate nuclei in the mesoporous silica material resulted in a highly ordered 2D-hexagonal mesoporous material with evenly dispersed crystalline NaZnPO₄ microdomains in its matrix using the self-assembly of cationic surfactant under hydrothermal synthesis condition. Four samples with different Si:Zn:P:Na mole ratios have been prepared. X-ray diffraction (XRD) patterns of the as-synthesized as well as template-free samples indicated the presence of mesophase in each case. N₂ adsorption data indicated mesoporosity in the samples together with the existence of crystalline NaZnPO₄ phase for the materials synthesized with Si/Zn mole ratio 5-12. ²⁹Si MAS NMR results showed high value of the Q⁴/Q³ ratio in these materials suggesting highly crosslinked structure.     

调控表面活性剂浓度制备单分散SBA-15介孔材料

采用溶胶-凝胶水热法,调控反应参数和反应工艺制备SBA-15介孔材料。通过扫描电镜、透射电镜、X射线衍射以及氮气吸附-脱附分析表征表明,在一定范围,随着表面活性剂浓度增加,介孔材料SBA-15形貌出现由球形、陀螺形到米粒状的变化,介观有序度提高。在反应物料P123与Si物质的量比为0.012时,介孔材料的物性常数如晶面间距、比表面积、孔体积和最可几孔径较小。采用静态陈化-水热法研究不同表面活性剂浓度对介孔材料形貌演变的影响,为有效调控SBA-15介孔材料形貌提供必要依据。     

镧系金属掺杂MCM-41的合成、表征及其脱硝性能研究

以正硅酸乙酯、硝酸镧、硝酸铈为原料,十六烷基三甲基溴化铵作模板剂,水热条件下合成镧、铈掺杂介孔分子筛。采用 XRD、FT-IR和氮气吸附脱附等对镧系金属掺杂MCM-41 进行表征,并以氨为还原剂研究其选择性催化还原一氧化氮活性以及反应条件（包括镧系掺量、反应温度、空速、氨氮比等）对催化性能的影响。本文旨在掺杂镧系金属提高分子筛的脱硝性能。镧系掺杂的分子筛改变了骨架增强了反应活性,稀土金属的高电荷密度使分子筛催化活性提高。结果表明,镧系金属镧、铈成功进入MCM-41 介孔材料的骨架内并保持有序的六方介孔结构,随着镧系掺杂量的增加,介孔有序性降低。当n（镧系金属）/n（硅）=0.04 、空速为4 000 h-1、n（氨气）/n（一氧化氮）为1 时 Ln-MCM-41催化剂在350 ℃反应时能保持较高活性。镧系掺杂的介孔分子筛能更有效地提高催化性能。     

Synthesis, characterization of high Ti-containing Ti-MCM-41 catalysts and their activity evaluation in oxidation of cyclohexene and epoxidation of higher olefins

A series of titanium rich isomorphous substituted Ti MCM-41 and HMS materials have been synthesized with different Si/Ti ratios. The highest amount of Ti incorporated in synthesis gel is in TiMCM-41 (Si/Ti = 10). Whereas for TiHMS catalysts, Ti is incorporated up to Si/Ti = 50 successfully without forming any extra framework TiO₂. Cyclohexene epoxidation reaction with dry tert-butyl hydroperoxide (TBHP) as an oxidant has been studied to evaluate the catalytic properties of Ti substituted mesoporous catalysts. The effect of molar ratio of substrate:oxidant in this reaction has been studied and high conversion, high selectivity were achieved at 2: 1 molar ratio with TiMCM-41 (Si/Ti =25). Dry TBHP (in dichloromethane) and chloroform were found as good oxidant and solvent system for this reaction. Pure siliceous mesoporous silica and low `Ti' substituted mesoporous silicas were found to be efficient catalysts for oxidation of cyclohexene. An interesting variation of the selectivity from allylic oxidation to epoxidation during oxidation of cyclohexene was observed with an increase in the Ti amount in the mesoporous framework. The allylic oxidation of cyclohexene has been carried out using molecular oxygen as an oxidant and in the presence of a small amount of TBHP as initiator. Siliceous HMS materials gave better conversion compared to MCM-41 type of materials and other conventional silicas like silica gel, fumed silica etc. in allylic oxidation of cyclohexene. Epoxidation of higher cyclic olefins like cyclooctene, cyclododecene, cis-cyclododecene and linear olefins 1-Heptene, cis-2-hexene, 1-undecene was carried out over TiMCM-41 (Si/Ti = 25). Ti substituted mesoporous catalysts were characterized by elemental analysis, XRD, FTIR, UVDRS, ²⁹SiMASNMR, BET surface area and pore size distribution techniques.     

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.     

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.     

Aluminum impregnated silica catalyst for Friedel-Crafts reaction:Influence of ordering mesostructure

Friedel-Crafts alkylation of benzene with linear chain olefin (C10-C14),which is an important reaction of synthetic detergent,was studied via different catalysts of aluminum impregnated silica molecular sieves.AlCl3 was immobilized on silica molecular sieves with different channel structures,hexagonal packing channels network (SBA-15,MCM-41),and disordered channel network (SiO2,SiO2-Gel) by impregnation.XRD and N2 adsorption-desorption isotherms confirmed that the specific mesoporous structures were maintained for order channel network catalyst after impregnation.Catalytic activities were investigated under different conditions.The influences of channel structure were discussed.The results showed that catalyst based on mesoporous like SBA-15 had the highest catalytic activities and 2-LAB selectivity compared with other catalysts in this work.The highest 2-LAB selectivity was nearly 50％ when 1-dodecene conversion was nearly 100％.At low 1-dodecene conversion or higher benzene/1-dodecene molar ratio,2-LAB selectivity was nearly 60％.     

Effect of the cerium loading on the HMS structure. Preparation,characterization and catalytic properties

Ce–HMS mesoporous materials were prepared by incipient wetness method starting from HMS synthesized in acid condition. The effect of cerium quantity, in the range of Ce/Si atomic ratio 0.02–0.3, on its structure and properties was investigated. Results showed that the HMS hexagonal structure was maintained after the cerium adding. Furthermore, the surface area and the pore volume were reduced. The presence of the cerianite nanoparticles located within the HMS channels up to 0.05, thus covering the HMS surface at higher Ce/Si atomic ratio, was observed. The catalytic performances of the materials were tested in ethanol partial oxidation reaction.