MCM-41 Molecular Sieves Research Articles

ChemInform Abstract: The Synthesis of Spherical Mesoporous Molecular Sieves MCM-48 with Heteroatoms Incorporated into the Silica Framework.

ChemInform Abstract: The Synthesis of Spherical Mesoporous Molecular Sieves MCM-48 with Heteroatoms Incorporated into the Silica Framework.

Stabilization of ferroelectricity in KNO 3 embedded into MCM-41 molecular sieves

Measurements of the linear permittivity and third-order harmonic generation were carried out for KNO 3 loaded molecular sieves MCM-41 with pores of 37 and 26 Å in comparison with bulk potassium nitrate. The samples were warmed up to 423 and 463 K from room temperature. The ferroelectric phase III was shown to occur upon cooling in both nanocomposites after warming till 463 K when it emerges also in bulk KNO 3. Nanoconfinement led to the pronounced broadening of the temperature range of ferroelectricity. While under the thermal conditions when phase III does not arise in bulk KNO 3, ferroelectricity was found only within pores of 26 Å.

Direct electrochemistry and electrocatalytic properties of hemoglobin immobilized on a carbon ionic liquid electrode modified with mesoporous molecular sieve MCM-41

The direct electron transfer and electrocatalysis of hemoglobin (Hb) entrapped in the MCM-41 modified carbon ionic liquid electrode (CILE) were investigated by using cyclic voltammetry in 0.10 M pH 7.0 phosphate buffer solution (PBS). Due to its uniform pore structure, high surface areas and good biocompatibility, the mesoporous silica sieve MCM-41 provided a suitable matrix for immobilization of biomolecule. The MCM-41 modified CILE showed significant promotion to the direct electron transfer of Hb, which exhibited a pair of well defined and quasi-reversible peaks for heme Fe(III)/Fe(II) with a formal potential of −0.284 V (vs. Ag/AgCl). Additionally, the Hb immobilized on the MCM-41 modified carbon ionic liquid electrode showed excellent electrocatalytic activity toward H 2O 2. The electrocatalytic current values were linear with increasing concentration of H 2O 2 in a wide range of 5–310 μM and the corresponding detection limit was calculated to be 5 × 10 −8 M (S/N = 3). The surface coverage of Hb immobilized on the MCM-41 modified carbon ionic liquid electrode was about 2.54 × 10 −9 mol cm −2. The Michaelis–Menten constant K m app of 214 μM indicated that the Hb immobilized on the modified electrode showed high affinity to H 2O 2. The proposed electrode had high stability and good reproducibility due to the protection effect of MCM-41 and ionic liquid, and it would have wide potential applications in direct electrochemistry, biosensors and biocatalysis.

Structural, acidic and catalytic features of transition metal-containing molecular sieves in the transformation of C 4 hydrocarbon

MCM-41 mesoporous materials and silicoaluminophosphates (SAPO-5) were prepared by gel hydrothermal crystallization. Both series of materials were modified by transition metals (chromium or iron close to 1 wt%). The synthesized solids were characterized by chemical analysis, XRD, nitrogen adsorption–desorption isotherms, SEM, EPR, XPS, IR of ammonia or pyridine adsorption studies, and 29Si, 27Al and 31P NMR. The catalysts were evaluated in the n-butane isomerization in order to assess their properties with regard to alkane transformations. The properties of the solids were modified by adding metals that altered the morphology, structural features and acidic character of the solids and result in an efficient performance in the transformation of n-butane in comparison with the pure counterparts. The introduction of Cr or Fe enhanced the catalytic ability of silicoaluminophosphates to produce isobutane. Fe and Cr modified silicoaluminophosphates were shown to be more efficient in the transformation of n-butane in comparison with the MCM-41 analogues. However, the activity of these iron-containing molecular sieves was considered too low in comparison with performances of iron-modified modernite. This was ascribed to an initial redox C 4 activation step occurring in synergy with Brønsted sites with sufficient acid strength which is indeed higher than that provided by MCM-41 and SAPO molecular sieves.

Does Molecular Self-Association Survive in Nanochannels?

tert-Butanol spontaneously forms supermolecular clusters in the liquid state. This phenomenon results from the balance between hydrogen(H)-bonded self-association and steric repulsion, which is ubiquitous in complex supermolecular assemblies. Neutron scattering provides direct insight into this mesoscopic order through a distinct signature (prepeak) in the structure factor. Using MCM-41 molecular sieves, we show that the spatial correlations associated with micelle-like clusters are totally suppressed in nanoconfined geometry. This is direct evidence of a considerable variation of the structure at the mescoscopic scale of an associated liquid during its manipulation in nanostructured materials and illustrates to what extent nanoconfinement affects the formation of the highly directional hydrogen-bonded systems and the properties of confined liquids in general.

Synthesis of [Si]-MCM-41 from TEOS and water glass: the water glass-enhanced condensation of TEOS under alkaline conditions

Mesoporous [Si]-MCM-41 molecular sieve systems have been fabricated by aging silica gels in CTAB both at RT and under hydrothermal conditions with or without stirring. For the synthesis involving water glass as a SiO2 source, optimal conditions (100 °C, pH 10, crystallization time 2–3 days) gave reproducible, highly ordered [Si]-MCM-41 materials in multi gram scale with high lattice parameter values and BET surface areas. The synthesis with TEOS as silica source produced an inferior quality material. A novel synthesis route involving the use of mixtures of the two precursors gave [Si]-MCM-41 with improved structural (XRD) and microstructural (HRTEM) long-range order. Addition of small amounts of water glass to a TEOS-based synthesis gel under stirred conditions produced [Si]-MCM-41 with excellent mesoporosity, long-range microstructural order, XRD and SBET properties. These properties are reminiscent of those for materials obtained from water glass as a sole SiO2 source. The advantage of this route is that it gave high-quality materials at relatively lower temperatures (80 °C) and shorter crystallization times (6 h) after 21 h aging at RT. The variation of the XRD d100 peak position, BET and HRTEM properties with [TEOS]/[water glass] ratio revealed that a ratio = 3.95 gave optimal production of the highly ordered materials. The data suggests that water glass acts as a structure-directing agent for the TEOS and is incorporated into the final structure.

Mn–MCM-41 molecular sieves: a selective gas-phase cyclohexanol oxidation catalyst

Mn–MCM-41 was synthesized by the hydrothermal method. The synthesized material was characterized by various physicochemical techniques such as small angle X-ray diffraction, elemental analysis, Fourier transform infrared spectroscopy and diffuse reflectance ultraviolet–visible spectroscopy. The gas-phase cyclohexanol and air reaction over Mn–MCM-41 molecular sieve was studied for the first time. The conversion is almost constant even up to 5 h, and follows a parabolic behavior with respect to temperature. The conversion reaches a maximum at 350 °C and selectivity towards cyclohexene is increased with temperature. The conversion and cyclohexene selectivity were increased with flow rate.

Synthesis of mesoporous MCM-48 using fumed silica and mixed surfactants

With mixed surfactants of cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100) as template agents and fumed silica as a silica source, mesoporous molecular sieves MCM-48 were hydrothermally synthesized under various conditions. Results indicate that high-quality MCM-48 was successfully prepared by substituting fumed silica for the traditional silica source of tetraethylorthosilicate. The effects of synthesis parameters such as quantity and composition of template agent(s), crystallization temperature, crystallization time, and the solution temperature to which fumed silica being added on the structure, morphology, relative degree of crystallization, and thermal stability of the resultant material were quantitatively investigated based on the analyses of XRD, N 2 sorption/desorption, and SEM. The optimized conditions for a high-quality MCM-48 were crystallization time of 60–84 h, crystallization temperature of 100 °C, and n(TX-100)/ n(CTAB) of 0.2. Moreover, it was found, for the first time, that the solution temperature to which fumed silica being added plays an important role for the synthesis of MCM-48, and n(TX-100)/ n(CTAB) ratio is crucial for the formation of pure MCM-48 structure.

Synthesis and Adsorption Property of Mesoporous Molecular Sieve MCM-41 from Iron Ore Tailings

The mesoporous molecular sieve MCM-41 was synthesized by hydrothermal synthesis method with iron ore tailings as starting material, and CTAB as appendage. The properties, kinetics and thermodynamics of Ni2+ from water adsorption process on MCM-41 residue were studied. The data demonstrated that the products possess typical properties of molecular sieve MCM-41, with specific surface area of 576 m2/ g, and the average pore size is 5.53 nm; the adsorption of MCM-41 residue to Ni2+ was decalescence reaction and the relationship between adsorbing capacity and equilibrium mass concentration is in accordance with the isothermal adsorption equations of Langmuir, and the removal rate of Ni2+ increases with the increasing of pH.

Synthesis and Characterization of Al MCM-41 Mesoporous Molecular Sieves

Al MCM-41 mesoporous molecular sieves were synthesized by a hydrothermal method at 110 ℃ using the cationic surfactant cetyltrimethylammonium bromide as a template, sodium silicate as the silicon source, and pseudoboehmite as the aluminum source. The obtained Al MCM-41 molecular sieve was characterized by X-ray powder diffraction (XRD), N2 adsorption-desorption, solid-state 29Si, 27Al magic angle spinning nuclear magnetic resonance (MAS NMR), scanning electron microscopy (SEM), and pyridine adsorption in Fourier transform infrared (FTIR) spectroscopy. The results showed that the Al MCM-41 molecular sieves had an ordered hexagonal packed structure, high relative crystallinity, high BET surface area, large pore volume, and a narrow pore size distribution. Furthermore, strong bonding between the silicon atoms in the Al MCM-41 framework resulted in good crystallization. The presence of the four-coordinate aluminum in the framework resulted in higher acidity.

Vapor phase alkylation of toluene using various alcohols over H3PO4/MCM-41 catalyst: Influence of reaction parameters on Vapor phase alkylation of toluene using various alcohols over H_3PO_4/MCM-41 catalyst: influence of reaction parameters on selectivity and conversion

A mesoporous MCM-41 molecular sieve material with a molar ratio of SiO_2/Al_2O_3 = 70 and loaded with H_3PO_4 was used as a catalyst for the alkylation of toluene, using various alcohols, namely methanol, iso-propanol, and tert-butanol, as alkylating agents. Para-alkylated toluene was the predominant product, formation of which was enhanced by moderate temperature, low amounts of the alkylating agents in the feed, and high carrier gas flow rate. Time on stream was found to exert a profound effect on the selectivity and conversion to the different products.

Microwave Hydrothermal Synthesis of Bimetallic (Ti-V) Ions Modified MCM-41 for Epoxidation of Styrene

AbstractMesoporous molecular sieves MCM-41 modified by single (Ti) and bimetal (Ti-V) ions with highly ordered hexagonal arrangement of their cylindrical channels were prepared by direct synthesis under microwave–hydrothermal (M–H) conditions at 403K. Characterizations with powder X-ray diffraction (XRD), 29Si magic-angle spinning (MAS) NMR, N2 adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelcctron spectra(XPS) and transmission electron microscopy (TEM) showed that Ti and V ions were introduced into MCM-41 under M-H conditions and Ti/V-Si bond was formed. Results revealed that all the samples were of a typical hexagonal arrangement of mesoporous structure. The modified materials were high active and selective in the epoxidation of styrene at 343 K in comparison with single-functional MCM-41. Moreover, compared to conventional method, the presented microwave hydrothermal synthesis of molecular sieves greatly improved the selectivity to styrene oxide, e.g., it reached 58.6% at styrene conversion of 18.7% over Ti-V-MCM-41 (50).

Facile and fast template removal from mesoporous MCM-41 molecular sieve using dielectric-barrier discharge plasma

Abstract Dielectric-barrier discharge (DBD) plasma, initiated at ambient condition, has been successfully applied for removing template from the mesoporous MCM-41 molecular sieve. The template removal rate using DBD plasma is eight times higher than the rate via thermal calcination. A perfect hexagonal pore structure was obtained after the template removal using the plasma, according to the characterization using the X-ray diffraction (XRD), transmission electron microscopy (TEM), and nitrogen adsorption analyses. The effectiveness of the plasma prepared mesoporous MCM-41 molecular sieve as the catalyst support has been confirmed using the Suzuki reaction with palladium as the active species.

Heterogenized Fe(III) phthalocyanine: Synthesis, characterization and application in liquid-phase oxidation of phenol

Tetra- tert-butyl substituted FePc(acac) complexes were supported upon mesoporous molecular sieves MCM-41 and SBA-15 via adsorption and coordination bondings as well as by covalent grafting. Prepared materials were characterized by UV–vis, MALDI, N 2-BET, SEM, TEM, FTIR, 13C, 29Si NMR and DSC–TG techniques. Supported FePcs exhibited high activity in liquid-phase oxidation of phenol with H 2O 2. The most resistant towards oxidative degradation were shown to be the covalently grafted FePc species.

Pulsed Nuclear Magnetic Resonance on 3He Adsorbed on Bare and 4He Preplated MCM-41 Using DC SQUID Detection

We report low field DC SQUID NMR measurements down to 1.5 K of 3He adsorbed in the pores of the mesoporous molecular sieve MCM-41. In the first experiment measurements were made on 3He adsorbed onto the bare pore walls of MCM-41 with coverages ranging from $n_{^{3}\mathrm{He}}=0.86n_{1}$ to full pores at $n_{^{3}\mathrm{He}}=1.79n_{1}$ , where n 1 is the coverage for monolayer completion. A second experiment was performed with low 3He coverages ( $n_{^{3}\mathrm{He}}\sim0.01n_{1}$ ) on 4He preplated pores, where a crossover to a quasi-1D state is expected to occur at temperatures sufficiently below 700 mK. In both experiments relaxation times T 1 and T 2 * were measured as a function of temperature and coverage at frequencies from 80 to 240 kHz. The frequency dependence of the linewidth in the pure 3He experiment is extremely weak therefore T 2 * ≈T 2. The 1.5 K isotherm shows a small minimum in T 2 * at a coverage corresponding to monolayer completion. In the experiment with 4He preplating there was no significant change in T 1 or T 2 * when the 3He coverage was doubled from $n_{^{3}\mathrm{He}}=0.01n_{1}$ to 0.02n 1 at a 4He preplating of $n_{^{4}\mathrm{He}}=1.05n_{1}$ . This suggests that the relaxation times are dominated by single particle effects in the low density regime.

Investigation of catalytic activities of new heterogeneous molybdenum catalysts in epoxidation of olefins

The mesoporous molecular sieve MCM-41 was covalently grafted with 3-aminopropyl trimethoxysilane and acetyl acetone (acac) successively to give modified MCM-41 (acacAmpMCM-41). Reaction of this material with amino acids, e.g. alanine, phenyl alanine, leucine, isoleucine, histidine and valine afforded the corresponding supported amino acid Schiff base ligands. Subsequent reaction with bis (acetylacetonato)dioxomolybdenum(VI) lead to various molybdenum complexes supported on MCM-41 through propyl chain spacer. Characterization of these materials was carried out with FT-IR, atomic absorption spectroscopy, powder X-ray diffraction (XRD) and BET nitrogen adsorption–desorption methods. The XRD and BET analyses revealed that textural properties of support were preserved during the grafting experiments. The resultant materials successfully catalyzed the epoxidation of cyclooctene, cyclohexene, 1-hexene and 1-octene with tert-butyl hydroperoxide (TBHP) to the corresponding epoxides.

MAS NMR studies of nanoporous matrices filled with sodium nitrite

The sodium nitrite NaNO2 incorporated into MCM-41 molecular sieves with pore sizes of 20, 26, and 37 A has been investigated by 23Na magic-angle spinning NMR spectroscopy. It has been demonstrated that the structure of the crystalline phase of the nitrite in a confined geometry is similar to the structure of bulk nitrite NaNO2. The direct proof of the diffuse melting of sodium nitrite in the pores has been obtained. The NMR signal of the molten sodium nitrite phase has been observed at temperatures close to the completion of the melting.

Carbon dioxide reforming of methane over nickel-grafted SBA-15 and MCM-41 catalysts

Mesoporous molecular sieves SBA-15 and MCM-41 supported Ni catalysts were prepared via a post-synthesis grafting method. The catalytic properties of these catalysts were investigated in CO 2 reforming of CH 4 under atmospheric pressure and compared with the impregnated catalysts. Characterization using powder X-ray diffraction, N 2 physisorption, H 2 temperature-programmed reduction, TG/DTA, Raman spectra and transmission electron microscopy techniques revealed that both catalyst preparation method and the nature of support play important roles in controlling the catalytic performance. The highest catalytic activity and long-term stability were obtained over a 5 wt.% Ni-grafted SBA-15 catalyst. This superior catalytic behavior was closely related with the strong resistance toward carbon formation and active metal sintering. Furthermore, the improved properties of the catalyst was caused by the formation of highly dispersed small Ni particles anchored by silica matrix, rather ordered pore structure, and structural stability of SBA-15 material under reaction conditions.

Platinum group metals substituted MCM-41 molecular sieves: Synthesis, characterization and application as novel catalysts for the reduction of NO by CO

Mesoporous MCM-41 molecular sieves with Si/M (molar) ratios of 100 containing platinum group metals (Pd, Pt, Rh, Ir) were synthesized by the hydrothermal method. These catalysts were systematically characterized by various analytical and spectroscopic techniques, viz., XRD, TEM, DRUV–vis, N 2 sorption. XRD analysis confirmed that the presence of platinum metals did not influence the parent structure and phase purity of the MCM-41 catalysts. DRUV–vis spectral studies of MCM-41 indicate the presence of platinum metal ions. The catalytic activities of these catalysts were evaluated for the reduction of NO by CO as a function of temperature. The study revealed that the catalytic activity is, in the order (Rh>Ir>Pd>Pt). Our experimental results are in good agreement with theoretical previous analysis based on the NO* dissociation activation energy.

Phase transitions in K1−xNaxNO3 embedded into molecular sieves

Dielectric studies of molecular sieves MCM-41 filled withK1−xNaxNO3 salts(x = 0, 0.05 and 0.10) were carried out and compared with results obtained for their bulkcounterparts. The regular increase upon warming of the temperature of the reconstructivephase transition from phase II to phase I with decreasing pore sizes was observed for allx. A thermodynamic model for shifts of reconstructive phase transitions was suggested.Ferroelectric phase III was shown to occur upon cooling in bulk binary salts and for allx in confined geometry under the thermal conditions when phase III does not arise in bulkKNO3. Ferroelectricity persisted below room temperature in the bulk binary salt withx = 0.10.