Showing papers on "MCM-41 published in 1999"
TL;DR: In this paper, two novel synthesis routes for the preparation of mesoporous MCM-41 materials are introduced, which use tetra-n-alkoxysilanes such as tetraethioxysilane (TEOS) or tetra n-propoxysilicane (TPS) as a silica source which are added to an aqueous solution of a cationic surfactant in the presence of ammonia as catalyst.
593 citations
TL;DR: The mesoporous sulfonic catalysts are also employed in the esterification of propanediols andmeso-erythritol, and for reactions with other fatty acids as mentioned in this paper.
328 citations
TL;DR: In this paper, highly ordered pure-silica MCM-41 materials possessing well-defined morphology have been successfully prepared with extremely low surfactant concentration at room temperature using TEM, XRD, and NMR techniques; and synthetic factors such as pH and amount of water have been investigated extensively.
232 citations
TL;DR: In this article, the formation of silica−surfactant mesostructures has been studied under various acidic conditions using tetraethyl orthosilicate and hexadecyltriethylammonium bromide.
Abstract: The formation of silica−surfactant mesostructures has been studied under various acidic conditions using tetraethyl orthosilicate and hexadecyltriethylammonium bromide. The synthesis conditions have been optimized in order to obtain the cubic (Pm3n) mesoporous molecular sieve designated as SBA-1 of high quality. The pore diameter of the SBA-1 material has been controlled within the range of 1.4−2.7 nm by expanding the surfactant micelles with 1,3,5-trimethylbenzene or substituting the hexadecyl group of the surfactant with other n-alkyl groups (C12H25 to C18H37).
184 citations
TL;DR: In this paper, a diffusion-controlled mechanism was proposed to explain the pore wall thickening and higher silica condensation in mesoporous MCM-41 silicas, which achieved Q4/Q3 ratios as high as 3.4 or 4.5 for two-step (48 h each) crystallization or 96 h crystallization at 150 °C.
Abstract: Thicker-walled mesoporous MCM-41 silicas with improved thermal and hydrothermal stability were prepared via secondary crystallization (in which calcined MCM-41 was used as silica source) or by using long crystallization times. Unusually, the thicker pore walls of the as-synthesized (surfactant containing) forms of these Si−MCM-41 materials are primarily made up of fully condensed silica units. Q4/Q3 ratios as high as 3.4 or 4.5 are obtained for two-step (48 h each) crystallization or 96 h crystallization at 150 °C, respectively. A diffusion-controlled mechanism in which silicate units and surfactant molecules are continually added onto the “seed” crystals (during secondary recrystallization) or to the growing surfactant/silicate aggregate (for long crystallization time) is proposed to explain the pore wall thickening and higher silica condensation.
173 citations
TL;DR: In this paper, a mesoporous aluminosilicate molecular sieve with MCM-41 type structure was synthesized using aluminum isopropoxide as the Al source.
Abstract: A mesoporous aluminosilicate molecular sieve with MCM-41 type structure was synthesized using aluminum isopropoxide as the Al source. Supported Co–Mo/MCM-41 catalysts were prepared by co-impregnation of Co(NO3)2·6H2O and (NH4)6Mo7O24 followed by calcination and sulfidation. For comparison, conventional Al2O3-supported sulfided Co–Mo catalysts were also prepared using the same procedure. These two types of catalysts were examined at two different metal loading levels in hydrodesulfurization of a model fuel containing 3.5 wt% sulfur as dibenzothiophene in n-tridecane. At 350–375°C under higher H2 pressure (6.9 MPa), sulfided Co–Mo/MCM-41 catalysts show higher hydrogenation and hydrocracking activities at both normal and high metal loading levels, whereas Co–Mo/Al2O3 catalysts show higher selectivity to desulfurization. Co–Mo/MCM-41 catalyst at high metal loading level is substantially more active than the Co–Mo/Al2O3 catalysts.
140 citations
TL;DR: In this article, a mesoporous molecular sieve MCM-41 with incorporated structural aluminum (Al-MCM41) was prepared by hydrolysis of a solution of tetraethoxysilane and aluminum isopropoxide in the presence of ammonia as a catalyst.
139 citations
TL;DR: In this paper, a pure silica mesoporous molecular sieve analogous to MCM-41 (Si-MCM41) was organofunctionalised with 3-aminopropyltrimethoxysilane.
Abstract: A pure silica mesoporous molecular sieve analogous to MCM-41 (Si-MCM-41) was organofunctionalised with 3-aminopropyltrimethoxysilane. The resulting organofunctionalised Si-MCM-41 ((NC3)Si-MCM-41) was suspended in alcoholic solutions of iron and copper salts to form the respective metal complexes (M(NC3)Si-MCM-41). Iron and copper were also incorporated into the framework of mesoporous MCM-41 metallosilicates (M-MCM-41) by hydrothermal synthesis. All these catalysts were employed in the liquid phase oxidation of cyclohexane with aqueous H2O2 (30%). The results show that the M(NC3)Si-MCM-41 are more active than the corresponding M-MCM-41. The activity of the catalysts decreases in the following order: Fe(NC3)Si-MCM-41≫Fe-MCM-41≫Cu(NC3)Si-MCM-41≫Cu-MCM-41. However, when the catalysts are recycled, leaching of the metals is observed. The good catalytic activity found for Fe(NC3)Si-MCM-41 can be attributed to the heterogenised iron complex.
114 citations
TL;DR: In this article, aluminum-containing mesoporous MCM-41 materials were prepared by post-synthesis modification of a purely siliceous MCM41 using different Al sources: AlCl3, aluminum isopropoxide and NaAlO2.
111 citations
TL;DR: In this paper, the addition of tetraalkylammonium or sodium ions to the synthesis gel results in considerable improvement of the hydrothermal stability of mesoporous molecular sieve MCM-41.
105 citations
TL;DR: In this paper, two mesoporous silica-aluminas (MSA and MCM-41) were compared with the amorphous microporous silicas-alumina (ERS-8) and the zeolite beta in the liquid-phase alkylation of toluene with propylene.
TL;DR: In this paper, a series of Cu 2+ -phthalocyanine and Co 2 + -perfluorophthalocyanines were synthesized inside the pores of MCM-41 by synthesis from o -dicyanobenzene.
Abstract: A series of Cu 2+ -phthalocyanine and Co 2+ -perfluorophthalocyanine has been prepared inside the pores of MCM-41 (MPcMCM-41) by synthesis from o -dicyanobenzene. The complexes were characterized by comparison of the UV–Vis diffuse reflectance and IR spectra with that of the same unsupported complexes. Transition metal ion exchange levels higher than 40% were found necessary for the success of the synthesis. o -Cyanobenzoic acid and phthalic anhydride were isolated as byproducts. Differential scanning calorimetry indicates that the complexes are more stabilized inside MCM-41 than within the supercages of Y faujasite. This has been interpreted as a reflection of the different conformations (planar for MCM-41 and distorted for Y faujasite) depending on the pore size of the host. The catalytic performance of novel MPcMCM-41 for cyclohexane oxidation was compared with that of the same unsupported complexes or when encaged within Y faujasite. tert -Butyl hydroperoxide was found as a more convenient oxidizing reagent than hydrogen peroxide. No leaching of the MPc or uncomplexed metal ions was observed. It was found that CoF 16 PcMCM-41 was more active and selective than CoF 16 PcY or unsupported CoF 16 Pc. However, in the case of the CuPc complex, the highest activity and selectivity was achieved using CuPcY. Our work shows the influence that the void dimensions of the porous host can play in the performance of metallophthalocyanines as oxidation catalysts.
TL;DR: In this paper, the influence of the chemical composition (Si/Al) and pore dimensions on activity and selectivity has been studied, and it has been found that a higher concentration of acid sites does not guarantee a better catalytic performance, and the adsorption-desorption properties of the material play a determinant role in this reaction where the two reactants and the product have very different polarities.
TL;DR: In this paper, a new perruthenate immobilized within MCM-41 has been used for clean oxidation of alcohols to carbonyl compounds with molecular oxygen.
TL;DR: In this article, the simultaneous removal of a surfactant template and attachment of trialkylsilyl groups has been successfully achieved by treating uncalcined MCM-41 with Trialkylchlorosilanes, resulting in the synthesis of mesoporous hydrophobic materials of highly uniform pore structure.
TL;DR: In this paper, sample controlled thermal analysis (SCTA) has been used to carefully and reproducibly eliminate the organic surfactant template from pure silica mesoporous MCM-41.
Abstract: Sample controlled thermal analysis (SCTA) has been used to carefully and reproducibly eliminate the organic surfactant template from pure silica mesoporous MCM-41. The reproducibility allowed a number of intermediate species to be isolated permitting complementary measurements. To understand the mechanisms by which the surfactant is removed, evolved gas analysis as well as 1H and 13C MAS NMR were used. The liberation of the porosity and evolution of the surface hydrophobicity were followed by gas adsorption, XRD and immersion microcalorimetry.It would seem that two types of cetyltrimethylammonium surfactant exist in the confined state, of which the large majority decomposes at a lower temperature (up to 200 °C) within the silica organic host than in the pure state. A small quantity of organic fragments are still observed within the pore structure up to 500 °C. Gas adsorption shows a pore blocking effect occurs during the surfactant removal.
TL;DR: The mesopores have an average pore diameter (APD) of ∼2.8-nm and are separated by walls 1.30-1.65-nm thick as discussed by the authors.
Abstract: Mesoporous silica and mesoporous silicates can be easily synthesized from the hydrothermal transformation at 110°C, of hydrogels with composition, M:25.95SiO 2 :5.2(C 2 H 5 ) 4 NOH:7.5(CH 3 (CH 2 ) 15 N(CH 3 ) 3 ) 2 O:790H 2 O, where M=0, Zr(OC 3 H 7 ) 4 or Ti(OC 4 H 9 ) 4 . These MCM-41 type crystals have Si/M molar ratio similar to the one in the parent hydrogel. After calcination at 600°C/12 h in air, the solids have surface area and pore volume in the 940–1740 m 2 /g range and 0.8–1.2 cm 3 /g range, respectively. The small mesopores have an average pore diameter (APD) of ∼2.8 nm and are separated by walls 1.30–1.65 nm thick. The isomorphous substitution of Si with Ti or Zr has little effects on pore size and on pore wall thickness. However, thermogravimetric analysis has indicated that charge compensating organic cations are located on different sorption sites and that site strength increases in the order: Si–OH Microcalorimetry experiments with NH 3 confirm that these materials are weak solid acids and that the introduction of Ti or Zr in the mesoporous silicate framework increases the solid's acidity. Acidity increases in the order: silica gel≪Si-MCM-41
TL;DR: In this article, MCM-41 mesoporous molecular sieves were synthesized at low temperature (343 K) in the presence of cetyltrimethylammonium bromide (CTMABr) and subjected to post-synthesis hydrothermal treatment at elevated temperatures (413 and 423 K).
TL;DR: In this paper, a tungsten-containing MCM-41 mesoporous molecular sieve was synthesized by the hydrolysis of tetraethylorthosilicate and ammonium tungstate in the presence of cetylpyridinium bromide as template in strongly acidic medium.
Abstract: A novel tungsten-containing MCM-41 mesoporous molecular sieve was synthesized by the hydrolysis of tetraethylorthosilicate and ammonium tungstate in the presence of cetylpyridinium bromide as template in strongly acidic medium. Physicochemical characterizations of this composite performed by means of powder X-ray diffraction, ICP atomic emission, FT-IR, laser Raman, and diffuse reflectance UV–Vis spectroscopy verified that tungsten ion could be isolated in framework positions of the MCM-41 mesostructure by this approach. Thermo-gravimetric study on this composite suggested that above 90% of the template encapsulated in the as-synthesized mesophase was recoverable by direct ethanol extraction. A catalytic test using hydrogen peroxide hydroxylation of cyclohexene as probe reaction proved that the framework tungsten site in the W-MCM-41 could afford the mesophase with fairly high activity in promoting this reaction, wherein acetic acid was found to be useful as solvent.
TL;DR: In this article, the effect of the structure and surface properties of support material on metallocene (zirconocene chloride) adsorption and catalyst activity in ethene polymerization was studied.
TL;DR: In this paper, the alkylguanidines were anchored to modified polystyrene or siliceous MCM-41, encapsulated in the supercages of zeolite Y, or entrapped in SiO 2 sol-gel matrices.
Abstract: Transesterification of soybean oil with methanol has been carried out in the presence of heterogenized alkylguanidines as catalysts. The alkylguanidines were anchored to modified polystyrene or siliceous MCM-41, encapsulated in the supercages of zeolite Y, or entrapped in SiO 2 sol-gel matrices. The catalytic activity of these catalysts was compared with that of their homogeneous counterparts, showing that the yields of methyl esters obtained in the homogeneous phase can be obtained with the guanidines anchored to the supports after longer reaction times. The catalysts prepared by immobilization of alkylguanidines in microporous systems showed diffusion restrictions for the vegetable oil as well as the low stability of the inorganic framework.
TL;DR: In this paper, post-synthetically prepared mesoporous derivatives using titanium butoxide grafting were catalytically active for the selective oxidation of 2,6-di- tert-butylphenol with H 2 O 2.
Abstract: Titanium-substituted mesoporous molecular sieves were prepared post-synthetically by applying Ti-butoxide in ethanol solutions of different concentrations to MCM-41, MCM-48, and KIT-1. The catalysts obtained were characterized by XRD, FT-IR, UV–Vis spectroscopies, XAS, and N 2 physisorption. Incorporation of Ti seems to promote further crosslinking of the mesoporous walls of the samples, and resulted in wall thickness increases. The post-synthetically prepared Ti-mesoporous derivatives using titanium butoxide grafting were catalytically active for the selective oxidation of 2,6-di- tert -butylphenol with H 2 O 2 . Their activities depended on the Ti concentration of the catalysts. Comparison works with hydrothermally prepared Ti-MCM-41, Ti-HMS or post-synthetically prepared Ti-mesopore catalysts, either using titanocene grafting or by TiCl 4 atom planting method, are also reported.
TL;DR: In this article, hexene was oligomerized in a down-flow tubular reactor holding a fixed catalyst bed at temperatures of 80-300°C and a pressure of 5 MPa.
TL;DR: Aluminium-containing mesoporous molecular sieves (AlMCM-41) with different Al contents (Si/Al=86.3, 43.9, 23.3 and 14.3) have been prepared using cetyltrimethylammonium bromide as an organic surfactant and characterized by XRD, MAS NMR, and N 2 sorption studies as discussed by the authors.
TL;DR: In this paper, a mesoporous titanium oxo phosphate was synthesized by a non-ionic template route (N 0 I 0 ), which is dominated by hydrogen bonding between self-assembled surfactant micelles and inorganic precursors.
TL;DR: The structural collapse of mesoporous molecular sieves by mechanical compression was found to occur mechanochemically through hydrolysis of Si-O-Si bonds as discussed by the authors. But their ordered structures were retained by compressing the well-dried samples under dry N2.
Abstract: The structural collapse of mesoporous molecular sieves, MCM-48 and MCM-41 materials by mechanical compression was found to occur mechanochemically through hydrolysis of Si–O–Si bonds. Their ordered structures were retained by compressing the well-dried samples under dry N2. Trimethylsilylation of mesoporous materials proved effective in eliminating their instability to compression through enhancing hydrophobicity.
TL;DR: The mesoporous molecular sieves of the MCM-41S family have little intrinsic catalytic activity, but it is possible to functionalize the material by grafting organic side chains on the walls as discussed by the authors.
Abstract: The mesoporous molecular sieves of the M41S family have little intrinsic catalytic activity. However, it is possible to functionalize the material by grafting organic side chains on the walls. These organic–inorganic hybrid materials maintain the advantages of the inorganic support, notably a high surface area and structural stability at elevated temperature and pressure. Catalysts based on MCM-41 functionalized with either hindered amine bases or free primary amino groups have been evaluated for the facile synthesis of monoglycerides from fatty acids and glycidol. Yields as high as 95% in 8 h have been achieved. The catalysts can be reused several times with little loss of activity.
TL;DR: The mesoporous silica molecular sieve MCM-41 can be obtained in a highly ordered form with various pore diameters if micelle packing is suitably controlled with a mixture of n-alkyltrimethylammonium bromide and n-alkyltriethylammiumbromide according to the length of the C12-C22 alkyl groups as mentioned in this paper.
TL;DR: The impregnation of H5PV2Mo10O40 polyoxometalate onto MCM•41 and amino modified MC•41 materials provided mesoporous active catalysts with large surface areas for aerobic hydrocarbon oxidation using isobutyraldehyde as a reducing agent as mentioned in this paper.
Abstract: The impregnation of H5PV2Mo10O40 polyoxometalate onto MCM‐41 and amino‐modified MCM‐41 materials provided mesoporous active catalysts with large surface areas for aerobic hydrocarbon oxidation using isobutyraldehyde as a reducing agent. The results of the oxidation of alkenes and alkanes gave product selectivities similar to those observed in the corresponding homogeneous reaction although catalytic activity was somewhat reduced. Under appropriate experimental conditions there was no leaching and the solid catalyst could be recovered and reused without loss in activity.
TL;DR: In this article, a one-pot liquid-phase procedure from carbonyl compounds and nitroalkanes using organic-diamine-functionalized mesoporous material (MCM-41) as the catalyst is described.
Abstract: Nitroalkenes are synthesised for the first time in a one-pot liquid-phase procedure from carbonyl compounds and nitroalkanes using organic-diamine-functionalised mesoporous material (MCM-41) as the catalyst. The yields are reasonable to excellent and the reaction conditions are mild. The hybrid solid base catalyst can be recycled several times with consistent activity.