Search results for "MCM-41"
showing 10 items of 52 documents
One‐Pot Synthesis of Superparamagnetic CoO‐MCM‐41 Nanocomposites with Uniform and Highly Dispersed Magnetic Nanoclusters
2004
Superparamagnetic CoO-MCM-41 mesoporous nanocomposites, with variable cobalt amounts, in the form of well-dispersed CoO-like clusters, were prepared in a large compositional range by a one-step reproducible procedure employing co-hydrolysis and co-condensation of the inorganic precursors in a water/triethanolamine medium. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Characterization of Nd-MCM41 obtained by impregnation
2008
Abstract Silica mesoporous molecular sieves (MCM-41), prepared by using micelles as template, were functionalized by means of incipient wetness method. Evidence for the neodymium presence in the silica matrix was obtained by means of EDX. SEM micrographs showed that impregnation does not change significantly MCM-41 morphology. The maintenance of the hexagonal structure was confirmed by XRD pattern analysis. However, the observed loss of long-range ordering, the cell parameter increase and the surface area decrease, observed by gas adsorption technique, were attributed to the introduction of neodymium oxide inside the MCM-41 mesochannels. By FT-IR and Raman spectra it was found that the main…
Direct oxidation of isobutane to methacrolein over V-MCM-41 catalysts
2004
High vanadium content mesoporous vanado-silicates with MCM-41-like structure, obtained by the atrane route, catalyse the direct oxidation of isobutane to methacrolein with 30% selectivity, and a total dehydrogenation (olefin plus methacrolein) selectivity up to 74%.
Degradation of silica particles functionalised with essential oil components under simulated physiological conditions
2020
[EN] In this work, the biodurability of three silica particle types (synthetic amourphous silica, MCM-41 microparticles, MCM-41 nanoparticles) functionalised with three different essential oil components (carvacrol, eugenol, vanillin) was studied under conditions that represented the human gastrointestinal tract and lysosomal fluid. The effect of particle type, surface immobilised component and mass quantity on the physico-chemical properties of particles and silicon dissolution was determined. Exposure to biological fluids did not bring about changes in the zeta potential values or particle size distribution of the bare or functionalised materials, but the in vitro digestion process partia…
MCM-41 silica effect on gel polymer electrolytes based on thermoplastic polyurethane
2012
Abstract Polymer electrolytes were prepared from thermoplastic polyurethane with addition of mixture of N-ethyl(methylether)-N-methylpyrrolidinium trifluoromethanesulfonimide (PYRA12O1TFSI) ionic liquid, lithium bis(trifluoromethanesulfoneimide) salt and propylene carbonate. MCM-41 mesoporous silica was added in proportions ranging from 5 to 20 wt.% with respect to TPU. The electrolytes were characterized by thermogravimetric analysis, differential scanning calorimetry, linear voltammetry and impedance spectroscopy. The MCM-41 addition to the system was found to improve the electrochemical stability of the membranes and to reduce the gel electrolyte/metallic Li interfacial resistance. The f…
Characterization and utilization of MFI zeolites and MCM-41 materials for gaseous pollutant adsorption
1999
Physisorption of n-hexane, trichloroethylene, tetrachloroethylene, carbon and nitrogen oxides on a microporous ZSM-5 (Si/Al=339) zeolite and an amorphous mesoporous MCM-41 (Si/Al=∞) sample was examined by isothermal thermogravimetry, manometry and calorimetry to evaluate the feasibility of using these porous materials for gaseous pollutant adsorption at room temperature. The adsorbents showed very interesting adsorption properties for hydrocarbons. ZSM-5 exhibited the strongest adsorption affinity and MCM-41 showed the largest adsorption capacity. Another main feature in this work was to observe a stepped-isotherm for the adsorption of C2Cl4 on ZSM-5. Such a substep located at very low rela…
Cracking Activity and Hydrothermal Stability of MCM-41 and Its Comparison with Amorphous Silica-Alumina and a USY Zeolite
1996
It has been found that the cracking activity of MCM-41 for a reaction catalyzed by strong acids site, such asn-heptane cracking, is much lower than that of a USY zeolite, and similar to that of amorphous silica-alumina. The higher activity of USY is due to the presence of stronger Bronsted acid sites in the zeolite. In the case of gas oil cracking, the greater accessibility of the large molecules to acid sites in MCM-41 relative to USY makes the difference in activity between these two catalysts much smaller than for the pure hydrocarbon. In the calcined state MCM-41 is more active and gives more gasoline and less gases and coke than amorphous silica-alumina. However, when the catalysts wer…
MCM-41 silica monoliths with independent control of meso- and macroporosity
2007
Centimetre sized macroporous silica monoliths consisting of MCM-41 have been prepared by a two-step procedure allowing an independent control of the meso- and macro-porosity. In the first step a monolith with a macroporosity tailored between 2 and 20 μm is prepared under acidic medium by a phase separation, named spinodal decomposition, leading to a bicontinuous structure of a silica/polymer phase and a water phase. The monolith is then reacted in an alkaline solution of cetyltrimethyl ammonium to transform the silica skeleton into MCM-41 under conditions which preserve the original morphology and macroporosity of the material. The combination of spinodal decomposition and pseudomorphic tra…
Rotational State Change of Acetonitrile Vapor on MCM-41 upon Capillary Condensation with the aid of Time-Correlation Function Analysis of IR Spectros…
2000
The infrared spectra of adsorbed acetonitrile on MCM-41 (porewidth = 3.2 nm) were measured at 303 K. In the CN stretching ν2 region, two bands were observed at 2265 cm− 1 and 2254 cm− 1, assigned to hydrogen-bonded molecules on surface hydroxyls of MCM-41, and physisorbed molecules in mesopores, respectively. We designate here the 2265 cm− 1 band as the ν2α band and the 2254 cm− 1 band as the ν2β band. The bandwidth of the fundamental transition ν2fβ, was obtained by removing the overlap with hot band transitions of the same mode, ν2α band, and other modes by least-squares fitting. Before capillary condensation, the relaxation time τ obtained from the bandwidth of the ν2fβ band was smaller …
Spontaneous doping and magnetic properties of polyacetylene and polypropyne synthesized in situ in Ni-exchanged mordenite and mesoporous MCM-41
2001
Upon polymerisation of acetylene and propyne inside the channels of Ni2+-exchanged mordenite and mesoporous MCM-41 spontaneous doping and formation of antiferromagnetic NiO clusters are observed to various extents. The population of polarons present in the final polymer/zeolite composite: (i) is higher for polyacetylene than for polypropyne; (ii) increases with polymerisation temperature in the range 100 to 335 °C; (iii) increases with the C content; and (iv) is higher for mordenite than for MCM-41 under the same conditions. The use of Ni(0),H+-mordenite for polymer formation enhances the polaron population of the resulting polymer by over one order of magnitude. Doped polyacetylene encapsu…