Showing papers on "MCM-41 published in 1997"
TL;DR: In this paper, a non-local density functional theory (NLDFT) model was used to obtain pore size characteristics of MCM-41 catalyst supports and vanadium-substituted MCM41 catalysts.
Abstract: A new method has been used to obtain pore size characteristics of MCM-41 catalyst supports and vanadium-substituted MCM-41 catalysts. The approach is based on the nonlocal density functional theory (NLDFT) model for nitrogen and argon adsorption in MCM-41, proposed recently. Samples with pore sizes varying from ca. 25 to 37 A were prepared by hydrothermal synthesis. Two synthesis procedures employing different sources of V were used to prepare V/MCM-41 catalysts. The samples were characterized by X-ray diffraction (XRD). N2 and Ar adsorption isotherms at 77 K were measured starting from the relative pressure P/P0 = 1 × 10-5. Analysis of adsorption isotherms was carried out in two stages. The first stage implies comparison of a given isotherm with a reference isotherm measured on a well-characterized sample of MCM-41 with uniform pores. From such a comparison, micropore volume, specific surface area of mesopores, and the point of the beginning of the capillary condensation are determined. In the second sta...
392 citations
TL;DR: The hydrogenation activity of Pt supported on two mesoporous MCM-41 samples differing in their chemical composition has been studied by following the kinetics of the hydrogenation of naphthalene at 225-275°C reaction temperature and 5.0 MPa total pressure.
238 citations
TL;DR: In this article, the authors show that up to 73% of the template in MCM-41 can be removed by extraction with solutions of an acid or salt in ethanol, and the resulting catalysts show high activity for the acetylation of 2-methoxynaphthalene.
199 citations
TL;DR: In this paper, a post-synthesis route through which various metal elements can be grafted onto siliceous frameworks using non-aqueous solutions of AlCl3, Al(NO3)3, SnCl2, Zn(O2CMe)2 Mn(O 2CMe), etc., is developed as a generalised means to obtain mesoporous metallosilicates molecular sieves with various structures such as MCM-41 (hexagonal), MCM48 (cubic Ia3d), SBA-1 (c
187 citations
TL;DR: Ruthenium(II) is a stable catalyst for alkene oxidation by tert-butyl hydroperoxide with high product turnover this article, and is used in this article.
184 citations
TL;DR: In this paper, the MCM-41 analogue mesoporous metallosilicates with high specific surfaces, containing the redox active metals Ti, V, Cr, Mn, Fe, or Co, were synthesized under reflux.
175 citations
TL;DR: In this article, vanadyl ions (VIVO)2+ were found to be the major vanadium species in the form of atomic dispersion on AFI by EPR and to exist simultaneously with tetrahedral (Td) V5+ in MCM-41 by UV−vis.
Abstract: Vanadium-containing silicate MCM-41 (V-MCM-41) zeolite and aluminophosphate AFI (VAPO-5) zeolite were synthesized and characterized by spectroscopic techniques. In as-synthesized form, the vanadyl ions (VIVO)2+ were found to be the major vanadium species in the form of atomic dispersion on AFI by EPR and to exist simultaneously with tetrahedral (Td) V5+ in MCM-41 by UV−vis. 29Si MAS NMR investigations suggested that the vanadium ions might attach to MCM-41 through interaction with the silanol groups on the internal wall of hexagonal tubes. The V5+ (in Td) ions are incorporated into the lattice of MCM-41 during synthesis, while the VO2+ (in Td) is the loosely bound V species. The results of Raman spectroscopy indicated that the rodlike aggregation of cationic surfactant (cetyltrimethylammonium bromide, CTAB) was encapsulated in the intrachannel space of synthetic MCM-41 as in an aqueous solution. After calcination and hydration, the V4+ species in as-synthesized V-MCM-41 was totally oxidized to +5 as shown...
128 citations
TL;DR: Palladium grafted mesoporous MCM-41 materials, prepared by vapor grafting, show remarkable activity in Heck carbon-carbon coupling reactions as discussed by the authors, demonstrating that the material can be used to construct mesopore MCM41 materials.
122 citations
TL;DR: In this paper, pure silica MCM-41 materials were synthesized at room temperature at different pH values ranging from 8.5 to 12.5, and the solids were characterized by XRD, 29Si-MAS-NMR spectroscopy and N2 and Ar adsorption measurements.
117 citations
TL;DR: In this article, a mesoporous niobium-containing silicate of the MCM-41 type was prepared for the first time, according to their knowledge, and its structure, mechanical stability, catalytic activity, and cation exchange properties were characterized and compared with those for aluminum-containing materials.
103 citations
TL;DR: The formation mechanism of the hexagonal MCM-41 and the lamellar MCM 50 mesoporous materials, prepared at room temperature with the surfactant cetyltrimethylammonium chloride (CTAC) and tetraet, was described in this article.
Abstract: The formation mechanism of the hexagonal, MCM-41, and the lamellar, MCM-50, mesoporous materials, prepared at room temperature with the surfactant cetyltrimethylammonium chloride (CTAC) and tetraet...
TL;DR: Synthetic methods for making an all-silica MCM-41 mesoporous silicate of high long-range order are reported in this article, which shows up to seven orders of X-ray diffraction and good stability under calcination conditions.
Abstract: Synthetic methods for making an all-silica MCM-41 mesoporous silicate of high long-range order are reported. The product shows up to seven orders of X-ray diffraction and good stability under calcination conditions. The greatest improvement in structure occurs when the pH is held between 9 and 10 during synthesis and the sulfate anion is present.
TL;DR: The acidity of Nb-MCM-41 molecular sieves as well as their hydrogen forms was studied using FTIR spectroscopy with pyridine and 2,6-dimethylpyridine as probe molecules and in test reactions (isopropanol and cumene decomposition) as mentioned in this paper.
Abstract: The acidity of Nb-MCM-41 molecular sieves as well as their hydrogen forms was studied using FTIR spectroscopy with pyridine and 2,6-dimethylpyridine as probe molecules and in test reactions (isopropanol and cumene decomposition). The number of Lewis acid sites (LAS) and Bronsted acid sites (BAS) was estimated from the intensity of IR bands at 1450 and 1549 cm-1 respectively. The acidity of niobium-containing materials was compared with that of Al related molecular sieves. The parent Al- and Nb-MCM-41 mesoporous materials studied in this work did not show Bronsted acidity which only appeared after ammonium exchange followed by calcination. The number and the strength of BAS was much higher on H,Al-containing material than that on H,Nb-containing molecular sieves. H,Nb-MCM-41 exhibited a higher concentration of LAS than H,Al related material.
TL;DR: In this paper, pure silica MCM-41 mesoporous molecular sieve material was synthesized and characterised by in situ synchrotron XRD, TEM, TGA/DTA and DRIFTS techniques.
Abstract: Pure silica MCM-41 mesoporous molecular sieve material was synthesised and characterised by in situ synchrotron XRD, TEM, TGA/DTA and DRIFTS techniques. In situ energy dispersive XRD (EDXRD) confirmed the exact nature of the pore diameter of MCM-41 and the change in crystal structure on calcination. The IR band at 1057 cm-1 of as-synthesised MCM-41 was shifted by 14 cm-1 on heating to 673 K due to increased condensation of silanol groups to form Si-O-Si bridges. Calcined MCM-41 materials were used to support Pd, and the catalytic activities for 1-hexene and benzene selective hydrogenation were investigated. The Pd/MCM-41 catalyst showed high activity in hydrogenation of 1-hexene at an inlet reaction temperature of 298 K, but did not show any activity in hydrogenation for benzene. TEM results for the reduced Pd/MCM-41 catalysts revealed that the average Pd particle size was around 2-2.5 nm and these particles were located in the pores of MCM-41 and showed good distribution. TPR measurements showed that about 70% of palladium oxide (PdO) loading in the calcined catalysts was reduced at sub-ambient temperature.
TL;DR: In this paper, the photocatalytic reduction of CO2 with H2O at 328 K was carried out using mesoporous zeolites with high reactivity for the formation of CH3OH.
Abstract: Ti-MCM-41 and Ti-MCM-48 mesoporous zeolites were prepared and investigations into the unprecedented use of these catalysts for the photocatalytic reduction of CO2 with H2O at 328 K were carried out. Ti-mesoporous zeolites exhibited high photocatalytic reactivity for the formation of CH3OH, its reactivity being much higher than bulk TiO2.
TL;DR: In this paper, the mesoporous structure of MCM-41 materials is characterized by X-ray powder diffraction, 27Al and 29Si MAS NMR, differential thermogravimetric analysis, N2 adsorption measurements, FT-IR and catalytic cracking of alkanes.
Abstract: Mesoporous Al-MCM-41 materials of different Si/Al ratios have been synthesized and characterized by X-ray powder diffraction, 27Al and 29Si MAS NMR, differential thermogravimetric analysis, N2 adsorption measurements, FT-IR and catalytic cracking of alkanes. The experimental results show that the incorporation of aluminium into the framework of MCM-41 has a great effect on the degree of long-distance order, the surface acidities and the mesoporous structures of the materials. With increase of the aluminium content, the amounts of tetrahedral framework aluminium and the acid sites on the samples increase, but the acid strength decreases. Al-MCM-41 materials exhibit high activity for n-C160 cracking and good selectivity for producing low carbon alkylenes, particularly for i-C4=.
TL;DR: In this paper, a mesoporous MCM-41 containing intraporous cesium oxide particles have been prepared by impregnation of aqueous Cesium acetate and subsequent calcination, and characterized by 133 Cs MAS NMR, CO 2 temperature programmed desorption and nitrogen physisorption.
Abstract: Mesoporous MCM-41 containing intraporous cesium oxide particles have been prepared by impregnation of aqueous cesium acetate and subsequent calcination, and characterized by 133 Cs MAS NMR, CO 2 temperature programmed desorption and nitrogen physisorption. The amount of framework aluminum of the MCM-41 support appeared to be very important regarding the strength of the basic sites. The Michael addition of diethyl malonate to neopentyl glycol diacrylate catalyzed by MCM-41 supported cesium oxide showed a high regioselectivity, in contrast to bulk cesium oxide.
TL;DR: In this paper, the pore diameter for MCM-41 samples from X-ray diffraction and adsorption data was calculated using the α s -plot, allowing for an accurate calculation of the specific surface area of the samples.
TL;DR: In this paper, the synthesis of titanium-containing MCM-41 mesoporous molecular sieves in the presence of dye molecules results in a well developed hexagonal structure if the powder dye is dissolved in a surfactant solution.
TL;DR: In this article, it was shown that post-synthesis hydrothermal restructuring is a convenient synthesis route to MCM-41 silicates with bimodal pore size distribution involving controllable amounts of microporosity.
Abstract: MCM-41 silicates prepared in the presence of octyltrimethylammonium bromide either by a conventional method or by post-synthesis hydrothermal treatment were characterized by nitrogen adsorption in a wide range of relative pressure from 10-6 to 1. Hydrothermally restructured samples were found to have lower BET surface areas, lower external surface areas and thicker silica walls than the non-treated sample. More importantly, in addition to their characteristic mesopores (ca. 3 nm), they were shown to have considerable amounts of micropores. The relative amount of micropores and mesopores was shown to be dependent on the treatment conditions. Thus, it is demonstrated that the postsynthesis hydrothermal restructuring is a convenient synthesis route to MCM-41 silicates with bimodal pore size distribution involving controllable amounts of microporosity.
TL;DR: In this article, the walls of the mesoporous silicate MCM-41 can be functionalised with 1,1′-ferrocenyl end groups by reaction with an alkane solution of======(1,1')-ferrocenediyl)dimethylsilane; the product is studied by======solid state NMR and EXAFS spectroscopies.
TL;DR: The chiral metallocene rac-ethylenebis(1-indenyl)zirconium dichloride, when immobilised on the surface of methylalumoxane-modified mesoporous silica MCM-41, is an effective catalyst for the production of highly isotactic polypropene with a unique spherulite morphology; Zr K-edge EXAFS studies of the organometallic-inorganic composite reveal not only an intact indenyl ligand framework after the immobilisation, but also the presence of a short Zr-
TL;DR: In this paper, the MCM-41/γ-Al2O3 catalyst presented mainly strong Lewis sties so that this material was activated by means of a liquid extraction method.
Abstract: Alkylation of toluene with isopropanol to produce isopropyltoluenes was investigated using a MCM-41 aluminosilicate as catalyst. The MCM-41/γ-Al2O3 catalyst presented mainly strong Lewis sties so that this material was activated by means of a liquid extraction method. It was observed that in the isopropylation of toluene, the isopropyltoluenes fraction contained more para isomer. This is due to the fact that MCM-41 materials contain relatively a few acid sites. In addition, the primary products of alkylation easily diffuse into the broad channels of this mesoporous framework.
TL;DR: In this article, the adorption isotherms of MCM-41 molecular sieve and catalysts exhibit two regions in their reversible parts and also two hysteresis loops.
Abstract: The adorption isotherms of MCM-41 molecular sieve and catalysts exhibit two regions in their reversible parts and also two hysteresis loops. The first hysteresis at relative pressure below 0.4 is assigned to the capillary condensation in the mesoporous channels, and it is sensitive to the filling or blockage in the channels. The adsorption isotherms together with XRD results can be used to characterize the dispersion of nickel and molybdenum oxides on MCM-41. MCM-41 supported Ni and Mo catalysts are in general more active than similar NaY supported catalysts, but they are more strongly dependent on the dispersion of metal oxides owing to the unidimensional channel system, of MCM-41.
TL;DR: In this paper, the incorporation of TS-1 and Ti-MCM-41 catalysts in PDMS is proven to enable the oxidation of hexane and epoxidation of C-cyclooctene.
TL;DR: In this article, the synthesis and characterization of a chiral amino-alcohol ((1R-2S)-ephedrine) immobilized on MCM-41 type mesoporous silicas (MTS: Micelle Template Silicas) is described.
Abstract: The synthesis and characterization of a chiral amino-alcohol ((1R-2S)-ephedrine) immobilized on MCM-41 type mesoporous silicas (MTS: Micelle Template Silicas) are described. The activity of these supported catalysts in the enantioselective addition of diethylzinc to benzaldehyde are reported, and compared with those obtained with the corresponding silica gel supported catalysts. The observed differences are discussed in terms of the nature of the grafting which depends on the support structure.
01 Nov 1997
TL;DR: In this paper, a mixture of seven and eight shell clusters (Pd7/8(phen)) was directly introduced into the mesoporous structure during the synthesis of MCM 41 as well as by incipient wetness impregnation.
Abstract: MCM 41 was loaded with ligand-stabilized palladium clusters in the size range of 3 -4 nm via different pathways. A mixture of seven- and eight-shell clusters (Pd7/8(phen)) was directly introduced into the mesoporous structure during the synthesis of MCM 41 as well as by incipient wetness impregnation. The samples were characterized by X-ray diffraction, N 2 -sorption, DTA and TEM. The clusters show different thermal stability depending on the synthesis pathway used. In situ incorporation leads to a decomposition of the Pd clusters after calcination at 873 K. However, the clusters that were introduced by incipient wetness impregnation are thermally stable up to 513 K in air. As a first catalytic test the oxidation of CO with synthetic air was used. Compared to catalysts prepared by conventional methods with appropriate palladium salts, the impregnated samples show high activity in the CO oxidation.
TL;DR: A mesoporous molecular sieve with binary transition metal (Zr-Cr) oxide framework has been synthesized for the first time, and the material exhibits good thermal stability with a high surface area.
TL;DR: In this article, a mesoporous material, MCM-41, with varying Si/Al ratios has been synthesised and characterised by adsorption, XRD, NMR, and FTIR measurements.
Abstract: Ordered mesoporous materials, MCM-41, with varying Si/Al ratios have been synthesised and characterised by adsorption, XRD, NMR, and FTIR measurements 27Al MAS NMR shows four-fold co-ordination of Al incorporated into the structure The combined study by microcalorimetry and FTIR, using acetonitrile as probe shows a few strong Lewis sites and only weak Bronsted acidity The physisorption properties were analysed by N2, n-hexane, benzene, acetonitrile, methanol and water adsorption using microcalorimetry and isotherm measurements MCM-41 shows adsorption behaviour of a well-defined mesoporous molecular sieve The heat of adsorption of a non-polar molecule is mainly determined by the pore diameter of the porous material A characteristic feature of all applied adsorptives is capillary condensation Whereas isotherms of water are completely irreversible and acetonitrile shows a small hysteresis, isotherms of the non-polar benzene, n-hexane, and nitrogen are completely reversible
Journal Article•
TL;DR: In this paper, high quality MCM-41 is prepared from a gel of molar composition SiO2: 0.20 CTACl:0.18 TMAOH:25 H2O aged at 20 ℃ for 24 hours before crystallization lasting for 48 hours.
Abstract: High quality MCM-41 is prepared from a gel of molar composition SiO2:0.20 CTACl:0.18 TMAOH:25 H2O aged at 20 ℃ for 24 hours before crystallization lasting for 48 hours. The (110) and (200) peaks of XRD pattern of high quality MCM-41 are unusually well resolved and the FWHM (full-width-at-half-maximum) of the (100) peak is 0.13° for as-prepared MCM-41 and 0.21° for calcined one, which indicate well-developed crystals. The properties of the crystal depend on the source and concentration of the reactants and the gel aging time. There is no induction period in the course of the synthesis, which is conveniently monitored by pH measurement. Gel aging, during which a spatial distribution of silicate polyanions and micellar cations is established, is essential for preparing high quality MCM-41. Surfactants with the same cationic organic group but different counteranions change the crystallization behavior. Highly basic gel (pH=12.6) favours the lamellar product; the quality of MCM-41 is lower as insufficient TMAOH is available to dissolve the silica.