Showing papers on "MCM-41 published in 1998"
TL;DR: Mesoporous silicas were functionalised with sulfonic acid groups, and the resulting materials are excellent catalysts for formation of bisfurylalkanes and polyol esters as discussed by the authors.
442 citations
TL;DR: Titanium oxide species included within the framework of mesoporous zeolites (Ti-MCM-41 and Ti- MCM-48) prepared by a hydrothermal synthesis exhibited high and unique photocatalytic reactivity for the reduction of CO2 with H2O at 328 K to produce CH4 and CH3OH in the gas phase as discussed by the authors.
319 citations
TL;DR: The Ru/M-41(m) catalyst can be used repeatedly, and 67% of its initial activity is retained after 11 691 turnovers (three runs), the loss of activity is attributed to catalyst leaching and/or deactivation.
Abstract: A ruthenium complex of meso-tetrakis(2,6-dichlorophenyl)porphyrin, [RuII(TDCPP)(CO)(EtOH)], is immobilized into mesoporous MCM-41 molecular sieves; the supported Ru catalyst can effect highly selective heterogeneous alkene epoxidations using 2,6-dichloropyridine N-oxide as terminal oxidant. Aromatic and aliphatic alkenes can be efficiently converted to their epoxides in good yields and selectivities, and cis-alkenes such as cis-stilbene, cis-β-methylstyrene, and cis-β-deuteriostyrene are epoxidized stereospecifically. Oxidation of cycloalkenes, e.g., norbornene and cyclooctene, can be carried out effectively using the heterogeneous Ru-catalyzed reaction while these alkenes are unreactive in the zeolite-based titanium silicate (TS-1)-catalyzed conditions (Murugavel, R.; Roesky, H. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 477). On the other hand, the Ru/M-41(m) catalyst displays size selectivity in the (+)-limonene oxidation where the terminal CC bond (vs internal trisubstituted CC bond) becomes more readi...
130 citations
TL;DR: In this article, a mesoporous MCM-41 mesopore material has been prepared by direct hydrothermal synthesis and a post-synthesis grafting method, which has been tested as catalysts for cyclohexene oxidation with aqueous H2O2 and tert-butyl hydroperoxide (TBHP).
Abstract: Framework Ti-substituted and Ti-grafted MCM-41 mesoporous material has been prepared by direct hydrothermal synthesis and a post-synthesis grafting method. The materials have been tested as catalysts for cyclohexene oxidation with aqueous H2O2 and tert-butyl hydroperoxide (TBHP). With aqueous H2O2 in methanol, the major products were cyclohexene diol and its methyl ethers. No cyclohexene oxide was produced. Titanium leaching was a serious problem, and the catalyst lost its activity irreversibly after only one cycle of reaction. With TBHP, the selectivity for cyclohexene oxide was near 100%, titanium leaching was negligible, and the catalyst could be repeatedly used after regeneration without suffering significant activity loss. However, the reaction rate was lower than when H2O2 was used. Framework substituted material and catalysts prepared by Ti-grafting onto a MCM-41 support behaved similar, but the Ti-grafted MCM-41 is somewhat more active. The turnover frequency (TOF) per mole of Ti decreases with an increase of Ti content in the catalyst. This is caused by a reduced Ti dispersion within the silica matrix.
119 citations
85 citations
TL;DR: In this paper, the use of MCM-41 mesoporous molecular sieve as the support for Pt for the selective catalytic reduction of NO by hydrocarbons in the presence of O2 was reported.
Abstract: First results are reported on the use of MCM-41 mesoporous molecular sieve as the support for Pt for the selective catalytic reduction of NO by hydrocarbons in the presence of O2. MCM-41 provided the highest specific NO reduction rates for Pt as compared with all other supports reported in the literature, i.e., Al2O3, SiO2 and ZSM-5.
83 citations
TL;DR: Ozone has been used to remove the organic surfactant species at 250 °C from as synthesised organic/inorganic composite materials to form mesoporous MCM-41 type solids with higher surface area, larger pores and narrower pore size distribution than those obtained by conventional calcination at 550 °C as mentioned in this paper.
82 citations
TL;DR: In this paper, a mesoporous silica-aluminas with a very narrow range of pore diameter such as MCM-41 and SAM have been used as catalysts.
81 citations
TL;DR: In this paper, the coordination state of aluminum in relation to the stability of mesoporous aluminosilicate MCM-41 following various treatments (vapor treatment and treatment in solution at different pH) is characterized using XRD, MAS NMR and BET techniques.
80 citations
TL;DR: In this paper, the chemisorption of trimethylaluminum on dehydrated mesoporous MCM-41 is described, and the sorption capacity of the silicate material is examined by addition of various amounts of the organoaluminum reagent and monitored by elemental analysis, FTIR spectroscopy, and nitrogen physisorsion measurements.
76 citations
TL;DR: It was observed that SnO(2) with higher surface areas had much higher sensitivities to hydrogen at 573 K and was synthesized using a cationic surfactant as a synthetic template using N-cetyl-N, N,N,N-trimethylammonium bromide as a template.
TL;DR: In this paper, the vapor phase Beckmann rearrangement of cyclohexanone oxime to caprolactam catalyzed by mesoporous molecular sieves was studied.
Abstract: The vapor‐phase Beckmann rearrangement of cyclohexanone oxime to ɛ‐caprolactam catalyzed by mesoporous molecular sieves was studied. The proton‐form mesoporous molecular sieves, H‐MCM‐41 and H‐FSM‐16, exhibited extremely high activity, selectivity and stability for ɛ‐caprolactam formation when 1‐hexanol was used as diluent. The weak acid sites and/or surface silanol groups of mesoporous molecular sieves play an important role in the selective ɛ‐caprolactam formation.
TL;DR: In this paper, the formation of a lamellar phase and its transformation into hexagonal MCM-41 were studied by powder X-ray diffraction (XRD), 29Si magic-angle-spinning (MAS) NMR and transmission electron microscopy (TEM).
Abstract: Mesoporous silicates synthesized in strongly basic media from sodium silicate in the presence of cetyltrimethylammonium chloride, a cationic surfactant. The formation of a lamellar phase and its transformation into hexagonal MCM-41 were studied by powder X-ray diffraction (XRD), 29Si magic-angle-spinning (MAS) NMR and transmission electron microscopy (TEM). The gel mixture (pH>14) is transparent. Upon acidification, a layered phase with interplanar spacing d=35 A rapidly forms at pH=13 and gradually transforms into the lamellar phase with d=31 A. The 29Si MAS NMR spectrum of the layered phase is broad and dominated by the resonance from Si(OSi)3O–M+ (Q3) structural units (M stands for the surfactant cation). The spectrum of the lamellar phase is well resolved with a more intense line from the Si(OSi)4 (Q4) structural units, indicating a more regular atomic arrangement. The hexagonal phase is obtained at pH=11.5 upon acidification of the gel, or when the pH of the intermediate product containing the lamellar phase is adjusted to 7–9 and the hydrothermal treatment continued. The hexagonal phase gives a broad 29Si NMR spectrum dominated by the Q4 resonance, indicating a less ordered local atomic arrangement in comparison with the lamellar phase. We suggest that the transformation is driven by the increasing reactivity of the silicate species with increasing acidity of the gel, which facilitates further aggregation of uncondensed silicate between the layers.
TL;DR: In this paper, a series of mesoporous materials with different Si/Al ratios were synthesized for hydrogenation of benzene, toluene and oxylene, and the acidities of catalysts were measured by the temperature-programmed desorption of ammonia (NH3−TPD) and IR spectra of pyridine.
Abstract: A series of Al‐MCM‐41 mesoporous materials with different Si/Al ratios are synthesized. The acidities of catalysts are measured by the temperature‐programmed desorption of ammonia (NH3‐TPD) and IR spectra of pyridine. Their catalytic activities for hydrogenation of benzene, toluene and o‐xylene are investigated on a pulse reactor system. NH3‐TPD and IR results show that only weak and medium acid sites could be observed on the catalysts, and the number of total acid sites decreases obviously with the increase of the Si/Al ratio whereas the medium acid sites are somewhat constant. The introduction of platinum onto Al‐MCM‐41 material decreases the total acid number by a small amount. The hydrogenation activities of the 1% Pt/HAl‐MCM‐41 catalysts are found to correspond well with the ratio of medium acid sites to total acid sites in the employed catalysts. It is proposed that, in addition to metal sites, the acid sites in the metal–acid interfacial regions are also the active sites for hydrogenation and the medium acid sites play important roles in the reaction.
TL;DR: In this article, Ga was substituted for Si with tetrahedral coordination in the Ga-MCM-41 structure, and it was confirmed that the framework Ga is the active site for aromatization.
TL;DR: Siliceous and aluminosilicate mesoporous molecular sieves (AlMCM-41) with variable framework Si/Al ratios have been used as supports to immobilize manganese 2,2,bipyridine (L) complex as discussed by the authors.
Abstract: Siliceous (SiMCM-41) and aluminosilicate mesoporous molecular sieves (AlMCM-41) with variable framework Si/Al ratios have been used as supports to immobilize manganese 2,2‘-bipyridine (L) complex c...
TL;DR: In this paper, a MCM-41/γ-Al 2 O 3 catalyst was used for isopropylation of benzene to produce cumene using a liquid extraction method.
Abstract: Alkylation of benzene with isopropanol to produce cumene was investigated using a MCM-41 aluminosilicate as catalyst. The MCM-41/γ-Al 2 O 3 catalyst, activated by means of a liquid extraction method, mainly contained strong Lewis acid sites. After the activity of the composite catalyst was stabilized, it was observed that, in the isopropylation of benzene, cumene was the major product. The high cumene selectivity could be due to the low acid site concentration in the MCM-41 material, and the rapid diffusion of cumene in the broad channels of this mesoporous framework.
TL;DR: A tungsten-containing MCM-41 mesoporous molecular sieve is synthesized by the hydrolysis of tetraethylorthosilicate and ammonium tungstate in the presence of cetylpyridinium bromide as template in acidic medium and found to be more active than the conventional WO3 catalyst in the hydroxylation of cyclohexene using H2O2 as oxidant.
TL;DR: In this paper, the catalytic properties of Pt, Rh and Co supported on mesoporous molecular sieves with MCM-41-type structure consisting of SiO2 and Al2O3 were studied for the reduction of NO with propene.
Abstract: The catalytic properties of Pt, Rh and Co supported on mesoporous molecular sieves with MCM-41-type structure consisting of SiO2 and Al2O3 were studied for the reduction of NO with propene. Pt supported on siliceous MCM-41 was the most active catalyst, however, significant quantities of undesirable N2O were formed during the reaction. Pt supported on mesoporous Al2O3 and Rh supported on both mesoporous oxides showed a lower activity, but an improved selectivity towards N2 formation. Co supported on MCM-41-type materials had only a low level of activity for the reduction of NO with propene. For Pt supported on MCM-41-type materials only a minor decrease in the activity was observed when water vapor was added into the reactant gas mixture, while on Rh- and Co-containing catalysts the activity strongly decreased.
TL;DR: Nanosized rhodium oxide-containing MCM-41 mesoporous molecular sieves are synthesized and characterized by XRD, TEM, N2 adsorption, NMR, XPS and EXAFS as discussed by the authors.
TL;DR: In this paper, the room-temperature synthesis of MCM-41 mesoporous compounds with high substitution levels of aluminium (Si / Al = 1.5) is achieved in a minimum time of synthesis.
Abstract: The room-temperature (RT) synthesis of MCM-41 mesoporous compounds with high substitution levels of aluminium (Si / Al = 1.5) is achieved in a minimum time of synthesis. The compound shows similar characteristics to hydrothermally synthesized materials. 27Al NMR study confirms the presence of tetrahedral aluminium in as-synthesized material as well as in the calcined material without observing the presence of octahedral aluminium after calcination.
TL;DR: In this paper, a systematic investigation of iron substituted mesoporous silicate (FeMCM-41) was carried out and the incorporation of the trivalent iron into the framework as well as the nature of such ions in the mesopore matrix was presented.
Abstract: A systematic investigation of iron substituted mesoporous silicate (FeMCM-41) was carried out. The incorporation of the trivalent iron into the framework as well as the nature of such ions in the mesoporous matrix is presented. The results are discussed in terms of the information obtained using various analytical techniques, viz., XRD, TG, DRUV-VIS, FTIR and ESR, as well as chemical analysis and surface area measurements.
01 Jan 1998
TL;DR: In this paper, the authors discuss the use of supercritical fluid extraction to avoid the costly calcination step during the material preparation and describe the M41S family of mesoporous materials.
Abstract: This article discusses the author's work with the M41S family of silicate/aluminosilicate mesoporous materials. It describes the use of supercritical fluid extraction to avoid the costly calcination step during the material preparation.
TL;DR: In this article, micellar associations of cetyltrimethylammonium chloride/hydroxide with different Cl/OH exchange ratios and new surfactants having crown-ethers groups as their polar head were used to prepare mesoporous materials of M41S family, with subsequent calcination or CO 2 supercritical fluid extraction to remove the template.
Abstract: In this study, micellar associations of cetyltrimethylammonium chloride/hydroxide with different Cl/OH exchange ratios and new surfactants having crown-ethers groups as their polar head were used to prepare mesoporous materials of M41S family, with subsequent calcination or CO 2 supercritical fluid extraction to remove the template. The influences of Cl/OH ratio, the size of the crown-ethers on the final phase and pore size were also investigated. The latter new templates were characterized by 1 H NMR and mass spectroscopy and the mesoporous materials by XRD, nitrogen physisorption and solid state 29 Si NMR spectroscopy.
TL;DR: Co-P-MCM-41 was used for the liquid oxidation of cyclohexane to adipic acid using a semi-batch autoclave reactor at 115°C and in a flow of 5 bar of oxygen.
Abstract: Co-P-MCM-41 catalyst was prepared by introduction of cobalt nitrate and phosphoric acid during gel-preparation for the synthesis of MCM-41. The catalyst, which was found to have very high surface area (995 m2/g), was tested for the one step liquid oxidation of cyclohexane to adipic acid using a semi-batch autoclave reactor (without addition of any promoter and solvent) at 115°C and in a flow of 5 bar of oxygen. The effect of the amount of catalyst on the induction time, catalytic conversion of cyclohexane, and selectivity to adipic acid was investigated. Depending on the amount of catalysts used in the reaction (from 0.1 to 3.0 g), an induction period from about 100 min to less than 10 min, cyclohexane conversion from 30 to 99%, and a selectivity to adipic acid from 15 to 40 %, could be achieved using Co-P-MCM-41 as the catalyst.