MCM-41 Structure Research Articles

Synthesis, Structural Characterization, and Photocatalytic Performance of Mesoporous W-MCM-48

Tungsten-containing mesoporous MCM-48 was synthesized by a rapid and facile room-temperature procedure. The mesoporous structure and the local environment of tungsten species were studied by powder X-ray diffraction, transmission electron microscopy, nitrogen adsorption isotherms, UV−visible diffuse reflectance spectroscopy, and Raman spectrometry. The long-range ordered mesoporous structure of MCM-48 was well preserved after tungsten incorporation. Tungsten oxide species were highly dispersed in the MCM-48 matrix, and no bulk crystalline WO3 was formed. The as-prepared W-MCM-48 materials show notable photocatalytic activity for hydrogen evolution from a methanol−water mixture under UV irradiation though bulk WO3 is not active for the reaction. The photocatalytic mechanism was studied by electron spin resonance spectroscopy.

Characterization of the diffusion path in micro- and meso-porous materials from ZLC analysis

It has been demonstrated that the main diffusion paths of micro- and meso-porous UL-zeolites could be characterized from the Zero Length Column (ZLC) desorption curves with an appropriate theoretical analysis (Malekian et al., in Ind. Eng. Chem. Res. 46:5067, 2007). The present work extends this method to study the ZLC desorption data of n-heptane/cumene/mesitylene in three mesoporous SBA-15 samples, 1-methylnaphthalene in MCM-48, cumene in SBA-16 and toluene/cumene in a microporous one-dimensional boron SSZ-42. The investigation results revealed that the structure of SBA-15, MCM-48 and SBA-16 behaved approximately as three-dimensional (isotropic) diffusion system, while SSZ-42 behaved as one-dimensional (anisotropic) diffusion systems. The diffusion path did not change within the measured temperature range, and by using different sorbate molecules. This work confirmed that this effective and relatively inexpensive method can be used as an additional tool for the characterization of porous materials.

Anomalous dynamics of water confined in MCM-41 at different hydrations

We present the results of molecular dynamics simulations on water confined in a silica pore of15 Å modelled to mimic the MCM-41 structure. We focus on the dynamical properties of waterfor different hydration levels of the pore. Density profiles show a well-defined double-layerstructure close to the surface. From the analysis of the layers we find that water moleculesclose to the substrate show an anomalous diffusion which is connected to thebehaviour of the residence time distribution. The interaction with the substrateinduces temporal disorder. As a consequence strong deviations are found from theMarkovian processes that usually determine the long-time diffusion properties.The residence time distribution of the water molecules in the inner part of thepore, far from the hydrophilic surface, is compatible with a Markovian process.

Thermal and hydrothermal stability of ZrMCM-41 mesoporous molecular sieves obtained by microwave irradiation

ZrMCM-41 mesoporous molecular sieves were synthesized by using the zirconium sulfate as zirconium source and using cetyltrimethyl ammonium bromide as a template under microwave irradiation condition. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), inductive coupled plasma (ICP) technique, Fourier transform infrared spectroscopy (FT-IR) and N2 physical adsorption, respectively. The effect of the different initial ZrO2: SiO2 molar ratio, the different thermal treatment temperature and hydrothermal treatment time on textural property was investigated. The results show that the obtained products possess a typical mesoporous structure of MCM-41 and have specific surface areas in the range of 598·1∼971·4 m2/g and average pore sizes in the range of ca. 2·46∼3·43 nm. On the other hand, the BET specific surface area and pore volume of the synthesized ZrMCM-41 mesoporous molecular sieve decrease with the increased amount of zirconium incorporated in the starting material, the rise of thermal treatment temperature and the prolonging of hydrothermal treatment time, the mesoporous ordering deteriorates. The mesoporous structure of the ZrMCM-41 mesoporous molecular sieve still retains after calcination at 750°C for 3 h or hydrothermal treatment at 100°C for 6 days, however, the mesoporous ordering is poor.

Characterization of mesoporous VO x/MCM-41 composite materials obtained via post-synthesis impregnation

Spherical-particle MCM-41 was synthesized at room temperature, and, then, impregnated with aqueous solutions of NH 4VO 3 to produce variously loaded VO x /MCM-41 composite materials. Bulk and surface properties of the materials thus produced were characterized by means of X-ray powder diffractometry (XRD), infrared spectroscopy (FTIR), N 2 sorptiometry and X-ray photoelectron spectroscopy (XPS). Results obtained indicated that subsequent calcination at 550 °C (for 2 h) of the blank and impregnated MCM-41 particles, results in materials assuming the same bulk structure of MCM-41, and exposing uniformly mesporous, high area surfaces ( P w = 2.0–2.3 nm; 974–829 m 2/g), except for the material obtained at 20 wt%-V 2O 5 that was shown to suffer a considerable loss on surface area (down to 503 m 2/g). XPS results implied that the immobilization of the VO x species occurs via interaction with surface OH/H 2O groups of MCM-41, leading to the formation of vanadate (VO 3 −) surface species, as well as minor V–O–Si and V 2O 5-like species. However, in all cases, the vanadium sites remained pentavalent and exposed on the surface.

Hydrothermal Stability of Ordered Mesoporous Titanosilicate Materials Prepared at Room Temperature

A study of hydrothermal stability, performed in boiling water under static conditions, of MCM-41 materials containing different titanium content, prepared by direct synthesis at ambient temperature and pressure, using tetraethoxysilane, titanium ethoxide and octadecyltrimethyl- ammonium bromide is presented. The behaviour is compared with pure silica grades prepared by a similar procedure. The samples were characterised by X-ray diffraction, adsorption of nitrogen at 77K and diffuse reflectance UV–Vis spectroscopy. It was found that the stability improves as the amount of titanium increases and that Ti-MCM-41 samples prepared with Si/Ti≤50 are significantly stable. After 12h in boiling water the pore size uniformity was practically maintained and only a small decrease in pore volume (5-9%), total surface area (2-7%) and mesopore width (3%) and a slight increase in pore wall thickness (3-6%) occurred. In contrast, some degradation of the MCM-41 structure for the pure silica and the lower Ti content (Si/Ti=100) samples was observed with the effect being less pronounced for the latter. The higher hydrothermal stability of titanium substituted samples is probably correlated with a higher degree of polymerisation of the pore walls and with the presence of extra framework titanium.

Grafting aluminum(III) 8-hydroxyquinoline derivatives on MCM-41 mesoporous silica for tuning of the light emitting color

Fluorescent materials ( Q) 3− n (2-BuO) n Al ( Q = 8-hydroxyquinoline, 2-methyl-8-hydroxyquinoline and 5-chloro-8-hydroxyquinoline, n = 1 or n = 2) were prepared in toluene by reacting aluminum 2-butoxide with 8-hydroxyquinoline and its derivatives. The compounds were characterized by 1H, 13C and 27Al NMR in solution, and the coordination status of the aluminum atom in the complexes were determined by 27Al NMR chemical shifts. The compounds were grafted on mesoporous silica (MCM-41) at room temperature without isolation of the complexes. The prepared materials were characterized by elemental analysis, FT-IR spectroscopy, low-angle X-ray diffraction (XRD), thermal analysis (TGA/DSC) and N 2 adsorption and desorption measurements. The results showed that the characteristic mesoporous structure of MCM-41 after grafting aluminum complexes remains intact. The photoluminescence (PL) properties of (Q) 3− n (2-BuO) n −1@Al–MCM-41 were investigated. The results revealed that the maximum wavelength is modulated by the MCM-41 guest.

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.

PMMA/mesoporous silica nanocomposites: effect of framework structure and pore size on thermomechanical properties

Mesoporous forms of silica (MS) with different framework structures and pore sizes, including hexagonal MCM-41 (2.4 nm), cubic MCM-48 (1.9 nm), hexagonal SBA-15 (7.0 nm) and mesocellular silicafoam MSU-F (24.8 nm), were examined as functional additives in the preparation of poly(methyl methacrylate) (PMMA)/mesoporous silica nanocomposites made by in situemulsion polymerization and compression molding. All of the composites at 5 wt% loadings of MS, exhibit improved thermal stability, an elevated glass transition temperature, and an enhanced storage modulus in comparison to the pristine polymer. MSU-F silica with the largest framework pore size provides the composite with the best improvement in thermomechanical properties. In general, the improvements in thermal stability and modulus diminish with decreasing framework pore size of the silica additive. For composites made from MCM-41 and MCM-48 silicas with similar pore sizes, the 3D MCM-48 structure provided superior benefits. The improvements in thermomechanical properties for the composite are attributed to the confinement of polymer in large pore channels, especially those with a 3D structure.

Preparation and catalytic properties of fine particles of Pt-Ge intermetallic compound formed inside the mesopores of MCM-41

Fine particles of Pt-Ge intermetallic compound were prepared by using mesoporous silica MCM-41 as a support and examined as a catalyst for H 2–D 2 equilibration and the hydrogenation of acetylene to clarify the catalytic properties of single-phase intermetallic compound with nano-order particle size. The mesopore structure of MCM-41 was not affected extensively by the introduction of Pt and Ge. Pt-Ge particles on MCM-41 gave very narrow particle-size distribution around 1.5 nm, suggesting the presence of Pt-Ge particles inside the mesopores of MCM-41, whereas those prepared on silica gel had the wide distribution of 1–6 nm. Though the Pt-Ge particles on MCM-41 were too small to identify their crystal phase by XRD, IR spectra of adsorbed CO indicated the presence of intermetallic phase, probably PtGe. Pt-Ge/MCM-41 showed lower catalytic activity than PtGe/SiO 2 for H 2–D 2 equilibration at 77 K and an induction period was observed for the former catalyst. The physically adsorbed hydrogen molecules may hinder the diffusion of HD through the mesopores. Pt-Ge/MCM-41 showed higher selectivity to ethylene than Pt/MCM-41 in the hydrogenation of acetylene, which again indicates the formation of PtGe intermetallic compound.

Synthesis, characterization and catalytic activity of copper incorporated and immobilized mesoporous MCM-41 in the single step amination of benzene

The paper reports the synthesis, surface and textural characterization of copper and amine modified MCM-41 and its application for the single step amination of benzene to aniline at 70 °C. Varying the amount of Cu different Cu/amine modified MCM-41 samples was synthesized by co-condensation and impregnation method. The samples were characterized by nitrogen adsorption–desorption, X-ray powder diffraction, Fourier-transform infrared spectroscopy (FT-IR), 29Si magic-angle spinning (MAS) and 13C Nuclear Magnetic Resonance (NMR) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). X-ray diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. FT-IR and DRS results indicated that Cu and amino groups are incorporated into the Si–O framework and frame wall respectively. NMR showed higher degree of condensation of materials in framework position. Cu-amine-MCM-41 samples showed significant catalytic activity for single step amination of benzene in acetic acid–water medium under mild reaction conditions using hydroxylamine as aminating agent. The Cu-amine-MCM-41 (Si/Cu = 20) showed highest benzene conversion (72.2%) and 100% selectivity for aniline.

Synthesis and characterization of magnetic mesoporous particles

Magnetic mesoporous particles were synthesized and their magnetic and structural properties are reported. The synthesis procedure consists of four steps: (i) preparation of magnetite colloidal nanoparticles; (ii) growth of a silica layer; (iii) development of the mesoporous structure and (iv) template removal. Two different methods for the template removal were studied and their effectiveness was discussed. Magnetization and Mössbauer spectroscopy measurements showed superparamagnetic behavior for the particles at room temperature. X-ray diffraction and nitrogen adsorption measurements showed a mesoporous MCM-41 structure with 2.48 nm pore diameter and 1023 m 2/g total area.

Ethylbenzene to chemicals: Catalytic conversion of ethylbenzene into styrene over metal-containing MCM-41

Isomorphously substituted (MeDM) and impregnated metal-containing MCM-41 (MeO x /IM) catalysts, in which Me = Co, Cu, Cr, Fe or Ni, have been prepared. Structural and textural characterizations of the catalysts were performed by means of X-ray diffraction (XRD), chemical analysis, Raman spectroscopy, electron paramagnetic resonance (EPR), N 2 adsorption isotherms and temperature programmed reduction (TPR). Cu 2+, Co 2+, and Cr 4+/Cr 3+ species were found over the catalysts as cations incorporated in the MCM-41 structure (MeDM) or highly dispersed oxides on the surface (MeO x /IM). The MeDM catalysts exhibited a good performance in the dehydrogenation of ethylbenzene with CO 2. However, MeO x /IM catalysts had a low performance in styrene production (activity less than 15 × 10 −3 mmol h −1 and selectivity for styrene less than 80%) due to the high reducibility of the metals species. However, Ni 2+ or Fe 3+ coordinated with the MCM-41 framework, as well as NiO x and Fe 2O 3 extra-framework species, is continuously oxidized by the CO 2 to maintain the active sites for dehydrogenating ethylbenzene. Deactivation studies on the FeDM sample showed that Fe 3+ species produced active sp 2 carbon compounds, which are removed by CO 2; the referred sample is catalytically selective for styrene and stable over 24 h of reaction. In contrast, highly active Ni 2+ and Ni 0 species produced a large amount of polyaromatic carbonaceous deposits from styrene, as identified by TPO, TG and Raman spectroscopy. An acid–base mechanism is proposed to operate to adsorb ethylbenzene and abstract the β-hydrogen. CO 2 plays a role in furnishing the lattice oxygen to maintain the Fe 3+ active sites in the dehydrogenation of ethylbenzene to form styrene.

Surface characterization and catalytic evaluation of copper-promoted Al-MCM-41 toward hydroxylation of phenol

The Mobil Composition of Matter No. 41 (MCM-41) containing Cu and Al with Si/Al ratios varying from 100 to 10 and 1 to 6 wt.% of Cu was synthesized under hydrothermal and impregnation conditions, respectively. The samples were characterized by nitrogen adsorption–desorption measurements, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), and 29Si and 27Al magic-angle spinning–nuclear magnetic resonance (MAS–NMR) spectra. X-ray diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. TPR patterns show the two-step reduction of Cu species. TPD study shows that Cu-impregnated Al-MCM-41 samples are more acidic than Al-MCM-41. From the MAS–NMR it was confirmed that most of the Al atoms are present tetrahedrally within the framework and some are present octahedrally in extraframework position. Impregnation of Cu shifted Al to the extraframework position. The catalytic activity of the samples toward hydroxylation of phenol in aqueous medium was evaluated using H 2O 2 as the oxidant at 80 °C. The effects of reaction parameters such as temperature, catalyst amount, amount of H 2O 2, and solvent were also investigated. Sample containing 4 wt.% copper-loaded Al-MCM-41-100 showed high phenol conversion (78%) with 68% catechol and 32% hydroquinone selectivity.

The oxidation of sulfide to sulfoxide on Ti-complex/MCM-41 catalyst

The heterogeneous Kagan-type catalyst was prepared by an in situ method using MCM-41 as support. The influence of the incorporation process on the structure of MCM-41 was studied using XRD, FT-IR, UV-vis, 29Si-MAS-NMR and N2 adsorption–desorption. The obtained materials showed a definite catalytic activity on the oxidation of sulfide to sulfoxide in the medium containing dichloromethane (solvent) and H2O2 or TBHP (oxidant).

Molecular Aggregation State and Photovoltaic Properties of Chlorophyll-Doped Conducting Poly(3-hexylthiophene)/MCM-41 Nanocomposites

Chlorophyll (Chl) was immobilized into a 1,4-butanediol-modified MCM-41 (BMCM-41) intercalated by poly(3-hexylthiophene) (P3HT) to form BMCM-41/P3HT/Chl nanocomposites having P3HT contents of 10, 30, 60, and 90 wt % from a solution-casting method. Wide-angle X-ray diffraction and transmission electron microscopy studies indicate that the pore structure of MCM-41 was retained after surface modification and a subsequent P3HT intercalation process. Scanning electron microscopy images showed that the BMCM-41 nanoparticles dispersed into the polymer matrix of BMCM-41/P3HT/Chl, and the sample with 10 wt % P3HT content gives the most homogeneous nanoparticle dispersion. Nitrogen adsorption-desorption results confirmed that the P3HT intercalation and Chl immobilization inside the BMCM-41 mesopore were successfully carried out. The pore volume and surface area of BMCM-41 decreased significantly when the amount of P3HT was increased from 10 to 90 wt %. The UV-vis study showed a blue shift of the pi-pi* transition band of P3HT in the spectra of BMCM-41/P3HT/Chl nanocomposites. The FT-IR study indicates an increase of the thiophene ring stretching and a decrease of the C horizontal lineO stretching when P3HT and Chl were inside the mesopore. The photovoltaic property of Chl-doped P3HT was improved significantly upon the addition of BMCM-41 nanoparticles, and BMCM-41/P3HT-10/Chl exhibits the highest incident photon-to-current conversion efficiency of 7.16%.

Amine functionalized MCM-41: An active and reusable catalyst for Knoevenagel condensation reaction

This paper reports preparation, characterization of amine modified mesoporous crystalline MCM-41 and its application in Knoevenagel condensation reaction. Amine modified MCM-41 was prepared by co-condensation and post-synthesis methods. The samples were characterized by X-ray powder diffraction, Fourier-transfer infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron micrograph (SEM), 29Si magic-angle spinning (MAS), nuclear magnetic resonance (NMR), diffuse reflectance spectra (DRS), nitrogen adsorption–desorption and CHN analysis. X-ray diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. SEM study exhibits that the arrangement of particles for 12.8% amine modified MCM-41 is well ordered and spherical in nature. CHN analysis supports that complete hydrolysis of ethoxy groups take place in 12.8% amine modified sample. From the NMR study it is confirmed that the surface coverage is 40% in 12.8% amine modified sample. The base catalytic activity of hybrid MCM-41 materials such as amine (post-synthesis and co-condensation methods) and surfactant functionalized materials for condensation reaction between benzaldehyde and diethyl malonate in solvent free, room temperature synthesis of cinnamic acid was evaluated and correlated with the surface and textural properties. Sample containing 12.8 wt% amine loaded by co-condensation method showed highest malonic ester conversion (92%) and selectivity (98%) for cinnamic acid.

Characterization of AlMCM-41 synthesized with rice husk silica and utilization as supports for platinumiron catalysts

RH-MCM-41 was synthesized by using silica from rice husk and further modified to increase acidity by adding Al with grafting method with Si/Al ratio of 75 and 25. The resulting materials were referred to as RH-AlMCM-41(75) and RH-AlMCM-41(25). The XRD spectra of all RH-AlMCM-41 confirmed a mesoporous structure of MCM-41. Surface areas of all RH-AlMCM-41 were in the range of 700-800 m2/g, lower than that of the parent RH-MCM-41, which was 1230 m2/g. After Al addition the Si/Al ratios of RHAlMCM-41(75) and RH-AlMCM-41(25) were higher than that of the parent RH-MCM-41. The RH-AlMCM41 materials were used as supports for bimetallic platinum-iron catalysts, denoted as Pt-Fe/RH-AlMCM-41, with Pt and Fe amounts of 0.5 and 5.0% by weight, respectively. Results from TPR indicated that the presenceof Al might assist the interaction between Pt and Fe as the reduction temperature of iron oxides shifted to a lower value. All catalysts were active for phenol hydroxylation using H2O2 as an oxidant, for which the highest conversions were observed on the RH-MCM-41 material with the highest surface area. The acidity of the supports did not present a significant role in improving the catalytic performance.

Highly enhanced photocatalytic degradation of tetramethylammonium on the hybrid catalyst of titania and MCM-41 obtained from rice husk silica

A hybrid photocatalyst consisting of TiO2 and the mesoporous support was prepared by loading TiO2 nanoparticles on MCM-41 which was synthesized from silica obtained from rice husk (abundant agricultural waste in Thailand). The catalysts with varying content of TiO2 were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption, high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray (EDX) analysis and UV–vis diffuse reflectance spectroscopy. The MCM-41 structure was retained after the loading of TiO2 but its surface area decreased as a result of the partial pore blocking. The TiO2 morphology and band gap were not affected by the dispersion on the support but the presence of the support prevented the TiO2 nanoparticles from agglomerating in the neutral pH range. When the TiO2 loading on the support was higher than 10wt.%, the activity of the hybrid catalyst was saturated. The activity of TiO2/MCM-41 for the photocatalytic degradation of tetramethylammonium (TMA) in aqueous slurry was significantly higher than that of the unsupported TiO2. The optimal TiO2 loading on the support was 10wt.% at which the complete conversion of TMA was achieved in 90min irradiation at pH 7. The unsupported TiO2 photocatalyst could convert only 20% of TMA in the same irradiation time and condition. The photocatalytic degradation of TMA proceeded by generating demethylated intermediates such as tri-, di- and monomethylammonium ions which were finally converted to ammonium ions.

Total oxidation of toluene over Pt–MCM-41 synthesized in a one-step process

Abstract Pt–MCM-41 materials were synthesized by a simple method via simultaneous self-assembling and Pt incorporation, using cetyltrimethylammonium chloride (CTAC) as a structure directing agent. Sample characterization was performed by N 2 sorption, XRD, TEM and high-resolution TEM (HRTEM) measurements. The highly ordered structure of MCM-41 was not appreciably affected by the formation of the Pt particles well dispersed in the MCM-41 as cubic nano-crystallite of ca. 10 nm. The Pt–MCM-41 sample was tested as a highly active catalyst towards complete oxidation of toluene. High surface area, well dispersed Pt, and appropriate Pt crystallite size may answer for the excellent catalytic performance.