Showing papers on "MCM-41 published in 2002"

Novel Polyethylenimine-Modified Mesoporous Molecular Sieve of MCM-41 Type as High-Capacity Adsorbent for CO2 Capture

Abstract: The objective of the work presented here is to develop a nanoporous solid adsorbent which can serve as a “molecular basket” for CO2 in the condensed form Polyethylenimine (PEI)-modified mesoporous molecular sieve of MCM-41 type (MCM-41-PEI) has been prepared and tested as a CO2 adsorbent The physical properties of the adsorbents were characterized by X-ray powder diffraction (XRD), N2 adsorption/desorption, and thermogravimetric analysis (TGA) The characterizations indicated that the structure of the MCM-41 was preserved after loading the PEI, and the PEI was uniformly dispersed into the channels of the molecular sieve The CO2 adsorption/desorption performance was tested in a flow system using a microbalance to track the weight change The mesoporous molecular sieve had a synergetic effect on the adsorption of CO2 by PEI A CO2 adsorption capacity as high as 215 mg-CO2/g-PEI was obtained with MCM-41-PEI-50 at 75 °C, which is 24 times higher than that of the MCM-41 and is even 2 times that of the pure

Adsorption of Chromate and Arsenate by Amino-Functionalized MCM-41 and SBA-1

Abstract: We report the characteristics of aminosilane-grafted mesoporous silicas as adsorbents of oxyanions in acidic conditions. Mono-, di-, and triamino-functionalized silicas were prepared to examine the influence of amino group density. The triaminosilane-grafted mesoporous silica adsorbed more chromate and arsenate than expected from the increased number of sites, suggesting stable complex formations. Functionalized SBA-1 showed larger adsorption capacities than MCM-41 derivatives. The adsorption capacity was independent of the average surface density of monoamino groups, demonstrating domain formation of fixed silanes. These structural characteristics on molecular and meso scales may offer insights into understanding the mechanism of heterogeneous oxyanion capture by amino-functionalized solids, which are promising inexpensive reagents for reducing toxic anion pollution.

Direct synthesis and characterization of titanium-substituted mesoporous molecular sieve SBA-15

Abstract: Ti-substituted mesoporous SBA-15 (Ti−SBA-15) materials have been synthesized by using a new approach in which the hydrolysis of the silicon precursor (tetramethoxysilane, TMOS) is accelerated by fluoride. These materials were characterized by powder X-ray diffraction patterns (XRD), X-ray fluorescence spectroscopy (XRF), N2 sorption isotherms, diffuse-reflectance UV−visible (UV−vis) and UV−Raman spectroscopy, 29Si MAS NMR, and the catalytic epoxidation reaction of styrene. Experiments show that Ti−SBA-15 samples of high quality can be obtained under the following conditions: F/Si ≥ 0.03 (molar ratio), pH ≤ 1.0, aging temperature ≤ 80 °C, and Ti/Si ≤ 0.01. It was found that the hydrolysis rate of TMOS was remarkably accelerated by fluoride, which was suggested to play the main role in the formation of Ti−SBA-15 materials of high quality. There is no stoichiometric incorporation of Ti, and the Ti contents that are obtained are quite low in the case of the approach that is proposed. The calcined Ti−SBA-15 m...

Evidence for general nature of pore interconnectivity in 2-dimensional hexagonal mesoporous silicas prepared using block copolymer templates

Abstract: Two-dimensional (2-D) ordered mesoporous silicas were synthesized following the literature synthesis procedures using two different silica sources (tetraethyl orthosilicate and sodium silicate) and poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) triblock copolymer template under acidic and neutral synthesis conditions. The resultant SBA-15 and MSU−H silicas exhibited highly ordered mesoporous structures and pore sizes in the range from 7.5 to 10 nm. The silicas prepared under acidic conditions were clearly microporous, as seen from comparative analysis of adsorption data, whereas the comparative analysis did not indicate microporosity for the silica prepared under neutral conditions. The ordered mesoporous silicas were used as templates for the synthesis of carbon inverse replicas, and in all cases, the 2-D hexagonally ordered mesoporous carbons of CMK-3 type were obtained. This provided a strong evidence that the presence of connecting pores between uniform, ordered, mesoporous channels o...

Selective etherification of glycerol to polyglycerols over impregnated basic MCM-41 type mesoporous catalysts

Abstract: In the general context of the development of the use of agricultural products for non-food applications, and particularly in the field of the glycerol valorisation (co-product of the triglycerides hydrolysis or methanolysis process), the selective etherification of glycerol was studied. The objective of this work is the direct and selective synthesis, from glycerol and without solvent, of polyglycerols having a low polymerisation degree (di- and/or triglycerol), in the presence of solid mesoporous catalysts. The main part of this study consists in the synthesis and the impregnation of mesoporous solids with different basic elements in order to make them active, selective and stable for the target reaction. The catalytic results obtained show that this impregnation method gives important activity, which must be correlated to an important active species incorporation. Concerning the selectivity of the modified mesoporous catalysts, the best value to (di-+tri-) glycerol are obtained over solids prepared by caesium impregnation. The re-use of these caesium impregnated catalysts does not affect the selectivity to the (di-+tri-) glycerol fraction. In the presence of lanthanum or magnesium containing catalysts, the glycerol dehydration to acrolein is very significant whereas this unwanted product is not formed when caesium is used as impregnation promoter.

MCM-41 functionalized with bipyridyl groups and its use as a support for oxomolybdenum(VI) catalysts

Abstract: The ordered mesoporous silica MCM-41 was covalently grafted with (3-chloropropyl)trimethoxysilane. Chloro substitution by the anion [4-CH2-4′-Me-2,2′-bipyridine]− gave a ligand-silica containing ca. 0.3 mmol bipyridyl groups per gram. Powder X-ray diffraction and nitrogen adsorption–desorption analysis demonstrated that the textural characteristics of the support were preserved during the grafting experiments and that the channels remained accessible, despite sequential reductions in surface area, pore volume and pore size. The coupling reactions were monitored by 29Si MAS NMR and 13C CP MAS NMR spectroscopy. Bipyridyl-functionalized MCM-41 exhibits a high encapsulating ability, as evidenced by its interaction with a dichloromethane solution of MoO2Cl2(THF)2. A material with a metal loading of 8.3 mass% was obtained. Molybdenum K-edge EXAFS analysis could not substantiate the formation of a tethered complex of the type MoO2Cl2(N–N), but instead indicated the formation of unidentate-bridged entities of the type [O2Mo–X–MoO2] with a metal–metal separation of 3.28 A. The molybdenum-containing MCM was active as a catalyst for the epoxidation of cyclooctene by tert-butyl hydroperoxide. However, this activity is due, at least in part, to leached molybdenum species in solution.

Anchored Pd complex in MCM-41 and MCM-48: novel heterogeneous catalysts for hydrocarboxylation of aryl olefins and alcohols.

Abstract: We report here, for the first time, synthesis of anchored Pd complexes in mesoporous supports such as MCM-41 and MCM-48 as true heterogeneous catalysts for hydrocarboxylation of aryl olefins and alcohols to give excellent conversion (∼100%) and regioselectivity (∼99%) for 2-arylpropionic acids. The catalysts were characterized by powder-XRD, 31P CP-MAS NMR, FT-IR, TEM, XPS and ICP-AES. Recycle studies with these anchored Pd mesoporous catalysts were performed to confirm true heterogeneity.

Manganese-containing MCM-41 for epoxidation of styrene and stilbene

Abstract: Mn-MCM-41 is found to be the most effective heterogeneous catalyst for the epoxidation of styrene with tert-butyl hydroperoxide (TBHP) among several metal ion-containing mesoporous molecular sieves including Mn-, V-, Cr-, Fe-, and Mo-MCM-41. ESR, XANES, diffuse reflectance UV–VIS, UV–Raman and XPS are used to characterize the Mn-MCM-41 synthesized by both direct hydrothermal (DHT) and template ion exchange (TIE) methods. The results suggest that Mn2+ and Mn3+ coexist in the Mn-MCM-41 samples synthesized by both methods and a large part of manganese atoms could be incorporated into the framework of MCM-41 obtained by the DHT method. The oxidation of either styrene or stilbene with TBHP as the oxidant over the Mn-MCM-41 produces corresponding epoxide as the main product; the reaction probably proceeds through a radical intermediate. The TIE catalyst shows higher activity, while the DHT catalyst gives higher TBHP efficiency for the epoxidation reactions.

Aluminum phthalocyanine complex covalently bonded to MCM-41 silica as heterogeneous catalyst for the synthesis of cyclic carbonates

Abstract: Aluminum phthalocyanine complex was covalently bonded to the silica surface of mesoporous MCM-41 molecular sieve via two different routes. The resulting anchored complex was characterized by X-ray powder diffraction (XRD), nitrogen adsorption and UV–VIS spectroscopy, and used as catalyst for the cycloaddition of CO 2 and epoxides to produce cyclic carbonates. Its catalytic activity can be markedly enhanced in the presence of a quaternary ammonium salt, such as n -Bu 4 NBr. The catalyst exhibits good stability as well as high catalytic activity in reaction conditions, and was subjected to utilization for 10 recycles without obvious loss of activity. The catalytic mechanism of the anchored aluminum phthalocyanine complex, combined with n -Bu 4 NBr as co-catalyst, for ring-opening of epoxides and activation of CO 2 are also discussed in detail.

Comparison of mesoporous Al-MCM-41 molecular sieves in the production of p-cymene for isopropylation of toluene

Abstract: Mesoporous aluminosilicate Al-MCM-41 with Si/Al=93 and 104 were synthesized using cetyltrimethylammonium bromide as the structuring agent and the materials were characterized using several techniques. The mesoporous structure was confirmed by X-ray diffraction (XRD) technique. The surface area, pore size and wall thickness was calculated by BET equation and BJH method using nitrogen sorption technique. Fourier transform-infrared (FT-IR) spectroscopy was used in order to obtain information on incorporated aluminum atoms in the mesoporous structure of Al-MCM-41. Thermogravimetric–differential thermal analyzer (TG–DTA) was used to determine the thermal stability of the materials. The effect of reaction temperature, WHSV and isopropanol:toluene ratios on the selectivity of p-cymene were studied. The Al-MCM-41 (93) catalyst exhibited excellent selectivity in the production of p-cymene by the isopropylation of toluene using isopropanol as the propylating agent.

Organically-modified mesoporous silica spheres with MCM-41 architecture

Abstract: New hybrid inorganic–organic materials displaying both an ordered mesoporous structure and spherical morphology have been synthesised by co-condensation of tetraethoxysilane and organoalkoxysilanes in water–ethanol solution containing ammonia in the presence of surfactant as templating agent.

Preparation and catalysis of DMY and MCM-41 encapsulated cationic Mn(III)–porphyrin complex

Abstract: The synthesis and characterization of the cationic manganese–porphyrin [meso-tetrakis(1-methyl-4-pyridinio)porphyrinato] manganese(III) penta-acetate complexes encapsulated in zeolite and mesoporous molecular sieve has been accomplished, and their catalytic activity was tested in the epoxidation of styrene and cyclohexene by iodosylbenzene. With mesoporous molecular sieve (MCM-41) and the new NaY zeolite (DMY) as supports, the encapsulated manganese–porphyrin systems show high activity and selectivity for the epoxidation. The effects of solvent and reaction time and the performance of the recovered catalysts have been studied. The mechanism of olefin oxidation has also been discussed. © 2002 Elsevier Science B.V. All rights reserved.

Sulfated zirconia supported in mesoporous materials

Abstract: SO 4 2− /ZrO 2 (SZ) supported on ordered mesoporous hexagonal materials were prepared by dispersion of ZrOCl 2 ·8H 2 O into the mesopores, followed by the hydrolysis and sulfation. These materials have been characterized by X-ray diffraction, nitrogen adsorption isotherms, infrared spectroscopy, and catalytic cracking of n -hexane, cumene and 1,3,5-triisopropylbenzene. The results show that SZ was successfully loaded into the inner pores of MCM-41; the as-synthesized catalyst showed favorable catalytic properties. The factors in the preparative process that affected the final activity were discussed.

Asymmetric Epoxidation of Styrene on the Heterogenized Chiral Salen Complexes Prepared from Organo-Functionalized Mesoporous Materials

Abstract: Organosilane-modified mesoporous materials have been prepared under mild and acidic conditions by a solvent evaporation method using C16TMABr surfactant as a template. The mesoporous samples synthesized in ethanol solvent by using this evaporation method showed a fully disordered pore system, but those obtained under hydrothermal conditions had highly ordered pores. The chiral salen Mn(III) complexes were immobilized on these organosilane-functionalized mesoporous silicas by a grafting method. The catalysts used in the asymmetric epoxidation of styrene and cis-stilbene and the effect of different mesoporous structures on the reactivity was investigated. Similar enantioselectivities were observed by using these heterogenized salen complexes as compared with reaction under homogeneous conditions.

Preparation of Highly Ordered Vanadium-Substituted MCM-41: Stability and Acidic Properties†

Abstract: Vanadium-substituted mesoporous molecular sieves (MCM-41) were prepared and the effects of water concentration, anti-foaming agent addition, pH adjustment, and Si/surfactant mole ratio were investigated. The hydrothermal and mechanical stability were tested for the pH-adjusted sample (Si/surfactant = 3.67 and 7.34). Catalysts were characterized by XRD, N2 physisorption, ICP, and 51V NMR. The acidic properties of synthesized V−MCM-41 were also examined by in-situ FTIR and TPD after pyridine adsorption. The increase of water concentration in the synthesis solution did not affect the physical properties of the resulting samples. The anti-foaming agent was very effective in improving the reproducibility of sample structure. The degree of vanadium substitution in the silica framework was increased with increasing water concentration and surfactant chain length. All of the incorporated vanadium was tetrahedrally coordinated in the silica framework. When the pH of the synthesis solution for V−MCM-41 was adjusted...

MCM-41 mesoporous molecular sieves supported nickel—physico-chemical properties and catalytic activity in hydrogenation of benzene

Abstract: Siliceous, aluminosilicate and niobosilicate mesoporous molecular sieves of MCM-41 type have been used as matrices for nickel incorporated via the wet impregnation. The N 2 adsorption, XRD, H 2 -TPR and Ni dispersion study were applied for the characterization of the prepared catalysts. The metal–support interaction (MSI) was the highest in Ni/NbMCM-41 material as indicated from H 2 -TPR results, in which the highest dispersion of nickel occurs. Hydrogen chemisorption strength and the reducibility of Ni-species are inversely proportional to MSI strength. Both parameters determine the catalytic activity of the mesoporous materials in the hydrogenation of benzene at higher temperatures (423–473 K), whereas their activity at lower temperatures increases with increasing Ni dispersion. The kinetic study allows the determination of the activation energy in the benzene hydrogenation on Ni/MCM-41 which is very low, 36.5 kJ mol −1 .