MCM-41 Mesoporous Materials Research Articles

Activity of B(OEt)3-MCM-41 catalyst in the MPV reduction of crotonaldehyde

Mesoporous silica material MCM-41 was functionalized with boron tri-ethoxide (B(OEt)3) groups by the grafting method and denoted as ‘B(OEt)3-MCM-41’. With the use of TEM, X-ray diffraction, high-resolution thermogravimetry (TGA) and N2 adsorption–desorption isotherms, it was shown that the initial hexagonal structure, the high specific surface area, and porosity are retained in the functionalized material. 29Si NMR- and 11B NMR- spectroscopies revealed that the surface of MCM-41 consists of boron alkoxide species. The Meerwein–Ponndorf–Verley (MPV) reduction of crotonaldehyde to but-2-en-1-ol was conducted in the presence of B(OEt)3-MCM-41 catalyst. MPV reduction of crotonaldehyde also showed that functionalization leads to the creation of Lewis acidic sites. A combination of mesoporous structure with Lewis acidic properties makes the MCM-41 functionalized with boron tri-ethoxide groups, useful as solid Lewis acid catalysts.

Isomerization of α-pinene oxide using Fe-supported catalysts: Selective synthesis of campholenic aldehyde

α-Pinene oxide, an oxygenated derivative of α-pinene, can be converted into various valuable substances useful as flavour, fragrance and pharmaceutical compounds. Campholenic aldehyde is one of the most desired products of α-pinene oxide isomerization being a valuable intermediate for the production of sandalwood-like fragrances. Iron modified zeolites Beta-75 and ZSM-5, mesoporous material MCM-41, silica and alumina were prepared by two methods (impregnation and solid-state ion exchange) and tested for selective preparation of campholenic aldehyde by isomerization of α-pinene oxide. The characterization of tested catalyst was carried out using scanning electron microscope analysis, nitrogen adsorption measurements, pyridine adsorption–desorption with FTIR, X-ray absorption spectroscopy measurements, XPS-analysis, 29Si MAS NMR and 27Al MAS NMR and X-ray diffraction. The isomerization of α-pinene oxide was carried out in toluene as a solvent at 70°C. The main properties influencing the activity and the selectivity are the acidic and structural properties of the tested catalysts. The highest selectivity of 66% was achieved at complete conversion of α-pinene oxide with Fe-MCM-41.

Facile synthesis and characterization of 12-tungstophosphoric acid anchoring MCM-41 mesoporous materials

HPW–MCM-41 mesoporous materials were firstly prepared via introducing 12-tungstophosphoric acid (HPW) into MCM-41 with an open synthesis process. The characterization results indicated that the materials retained the mesoporous structure of MCM-41 and bulk HPW was highly dispersed into MCM-41. Catalytic tests showed that HPW–MCM-41 exhibited good catalytic properties for the oxidation of benzaldehyde to benzoic acid with aqueous hydrogen peroxide solution, in the absence of any organic solvent and co-catalysts. The sample containing 10wt% HPW with larger surface area and pore volume was found to be more active than the others under the same reaction conditions.

Fe-MCM-41 from Coal-Series Kaolin as Catalysts for the Selective Catalytic Reduction of NO with Ammonia

Fe-MCM-41, one kind of high-ordered mesoporous materials catalysts, with molar ratio of Fe/Si = 0.01-0.1, was synthesized by hydrothermal method from coal-series kaolin. Fe-MCM-41 catalysts were characterized by Fourier transform infrared spectroscopy, high resolution transmission electron microscopy, N2 adsorption-desorption, x-ray photoelectron spectroscopy, and UV-vis spectroscopy. The results clearly indicated that: (1) all the samples exhibited typical hexagonal arrangement of mesoporous structure; (2) the incorporation of tiny amount of Fe3+ onto the surface and pore channel of MCM-41 mesoporous materials could efficiently promote the deNO x activity of these catalysts. Moreover, the Fe-MCM-41 mesoporous materials were evaluated in the selective catalytic reduction of NO with NH3. The results showed that Fe-MCM-41 catalyst with Fe/Si = 0.05 showed the highest catalytic activity at 350 °C, a gas hourly space velocity of 5000 h−1, n(NH3)/n(NO) = 1.1, and O2% = 2.5%.

Adjusting the Electronic and Optical Properties of Mesoporous MCM-41 Materials by Ti Doping

The objectives of this thesis are to understand the electronic structures of oxides and oxynitrides for photocatalytic water splitting, examine the Casimir interaction between oxides, and explore possible approach to bridge the Casimir force and material properties for advanced material research. The studies were performed in the framework of the density functional theory, many-body perturbation theory, i.e, the GW approximation and Bethe-Salpeter equation, as well as the Casimir-Lifshitz approach.The thesis consists of two sets of results. In the first part (papers I-VI), the electronic structures of oxynitrides, i.e., ZnO-GaN and ZnO-InN, with different compositions and local structures have been studied. The oxynitrides reduce the band-gap energies significantly compared to the binary counterparts, enabling the oxynitrides to act as visible light active photocatalysts. Formation of cluster--like structures further reduces the band-gap and delocalizes the valence bands, benefiting higher optical absorption. Furthermore, the energy levels between oxynitride and water were aligned using a surface model adapted from semiconductor heterostructure.In the second part (papers V-IX), the electronic structures of oxides as well as the Casimir interactions have been examined. In particular, we investigated the differences of optical and electronic properties between SnO2 and TiO2 polymorphs in terms of band-edge characters and electron-phonon coupling. In addition, we synthesized a mesoporous material possessing two types of pore structures (one is hexagonal ordered with pore diameter of 2.60 nm and the other is disordered with pore diameter of 3.85 nm). The pore framework contains four-coordinated titanium and oxygen vacancies, verified by both experimental measurements and density-functional theory calculations. Utilizing the predicted properties of the materials, we studied the Casimir interactions. A stable equilibrium of Casimir force is achieved in planar geometry containing a thin film and porous substrates. Both the force and equilibrium distance are tuned through modification of the material properties, for instance, optical properties and porosity. Furthermore, we adapted this concept to study the interactions between gas bubbles and porous SiO2 in water. A transition from repulsion to attraction is predicted, which highlights that the bubbles may interact differently at different surface regions.

SYNTHESIS OF MESOPOROUS MCM-41 MATERIALS WITH LOW-POWER MICROWAVE HEATING

Crystalline, high-surface-area, hexagonal mesoporous MCM-41 having uniform pore sizes and good thermal stability was successfully synthesized at 90°–120°C in 30 min using low-power microwave irradiation. This appears to be the first comprehensive and quantitative investigation of the comparatively rapid synthesis of mesoporous MCM-41 using low-power microwave heating of 80 W (90°C) and 120 W (120°C). The influence of reaction temperature and the duration of heating were carefully investigated, and the calcined MCM-41 materials were characterized by XRD, SEM, TEM, nitrogen adsorption, TGA, and FT-IR. The mesoporous MCM-41 product synthesized in 30 min at 120 W and calcined at 550°C had a very high surface area of 1438 m2/g and was highly ordered, containing uniform pores with diameters in the range of 3.5–4.5 nm. The wall thickness of the materials highly depended on the power of the microwave energy used during synthesis. Synthesis of the mesoporous MCM-41 products at 120°C resulted in a structure with thinner walls. The mesoporous MCM-41 materials synthesized in the present work had good thermal stability.

Effects of polar modifiers on supercritical extraction efficiency for organic template removal from mesoporous MCM-41 materials

The application of polar modifiers usually can make supercritical CO2 extraction more attractive in various potential applications. In this work, several polar modifiers have been examined for the extraction of the template cetyltrimethylammonium bromide (CTMABr) from newly synthesized MCM-41 mesoporous materials, and the modifier content, modifier identity and the sample matrix on supercritical CO2 extraction efficiency are then evaluated. The results show that the polar modifiers employed have strong influences on the template extraction efficiencies and this could be interpreted rather well in terms of solubility parameter and polarity of the modifiers. Methanol, water and acidic methanol are found to result in very high efficiencies of more than 85% for the pure siliceous samples while relatively good extraction efficiencies of 60–80% for aluminum incorporated samples, and the difference is due to that the organic template could form stronger interactions with the Al species than the silanol groups. Nitrogen adsorption/desorption and X-ray diffraction results confirmed that the polar modifiers have strong influences on the final mesoporous structure of the MCM-41 materials and with methanol modified supercritical CO2 extraction the resultant materials possess well-ordered mesostructure and much better structural properties like higher pore volume and specific surface area.

Synthesis and catalytic performance of novel hierachically porous material beta-MCM-48 for diesel hydrodesulfurization

Novel hierachically porous material Beta-MCM-48 was successfully synthesized from Beta zeolite seeds by two-step hydrothermal crystallization method using Cetyltrimethylammonium Bromide as the mesostructure directing agent. Beta-MCM-48 composite synthesized at the optimization conditions possessed Beta microporous structure and cubic Ia\( \overline{ 3} \)d mesoporous structure simultaneously. Meanwhile, the acidity of Beta-MCM-48 was similar to Beta zeolite and higher than MCM-48 mesoporous material. A series of Al2O3-Beta-MCM-48 supported NiMo catalysts with different Beta-MCM-48 contents were prepared by the incipient-wetness impregnation method. The catalytic performances were evaluated using DaQing Fluid Catalytic Cracking diesel as feedstock in a high pressure microreactor. Hydrodesulfurization results indicated that NiMo/Al2O3-Beta-MCM-48 catalyst exhibited better activities than that of NiMo/Al2O3 traditional catalyst. NiMo/Al2O3-Beta-MCM-48 catalyst obtained the highest activity as the Beta-MCM-48 content in the support was 20 wt %, and the corresponding sulfur content of the hydrotreated product reached to 23.02 μg g−1.

Selective Preparation of trans-Carveol over Ceria Supported Mesoporous Materials MCM-41 and SBA-15

Ce-modified mesoporous silica materials MCM-41 and SBA-15, namely 32 wt % Ce–Si–MCM-41, 16 wt % Ce–H–MCM-41 and 20 wt % Ce–Si–SBA-15, were prepared, characterized and studied in the selective preparation of trans-carveol by α-pinene oxide isomerization. The characterizations of these catalysts were performed using scanning electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption and FTIR pyridine adsorption. Selective preparation of trans-carveol was carried out in the liquid phase in a batch reactor. The activity and the selectivity of catalyst were observed to be influenced by their acidity, basicity and morphology of the mesoporous materials. The formation of trans-carveol is moreover strongly influenced by the basicity of the used solvent and in order to achieve high yields of this desired alcohol it is necessary to use polar basic solvent.

CO2 adsorption properties and thermal stability of different amine-impregnated MCM-41 materials

The adsorption properties of CO2 on MCM-41 mesoporous materials impregnated with ethylenediamine (EDA), tetraethylenepentamine (TEPA) and two kinds of polyethylenimines (PEI600 and PEI1800), respectively, were studied with mass spectrometry (MS) and thermogravimetry (TG) techniques. The sample obtained by impregnating EDA (EDA-MCM-41) showed a low CO2 adsorption capacity due to the ready volatilization of EDA, while those samples prepared by TEPA (TEPA-MCM-41), PEI600 (PEI600-MCM-41) or PEI1800 (PEI1800-MCM-41) exhibit higher adsorption capacity and thermal stability although the adsorption capacity decreased with increasing molecular weight of amines. A maximum CO2 adsorption capacity of 2.7 mmol/g was achieved on the TEPA-MCM-41 with 40% TEPA. When this sample was regenerated at 100°C under pure nitrogen atmosphere, its CO2 adsorption capacity was decreased by 7.4% after ten recycles in contrast to less than 1% for both PEI600-MCM-41 and PEI1800-MCM-41. However, when the regeneration atmosphere was changed to 80% CO2/20% N2, the regeneration temperature should be increased to more than 160°C for all the samples despite that PEI-MCM-41 showed high thermal stability than TEPA-MCM-41.

Synthesis of Mesoporous Material from Chrysotile-Derived Silica

Mesoporous MCM-41-type molecular sieves were synthesized using calcined and leached chrysotile and cetyltrimethylammonium bromide as the silica source and structure directing agent, respectively. Powder X-ray diffraction (XRD), N2 isothermal adsorption-desorption, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were used to characterize the samples. The calcined and leached chrysotile can be employed as an inexpensive silica source for the formation of low-order MCM-41 mesoporous materials.

A New Functionalized MCM-41 Mesoporous Material for Use in Environmental Applications

Este trabalho descreve a sintese e caracterizacao de um novo adsorvente mesoporoso que consiste o MCM-41 funcionalizado com o acido p-aminobenzoico modificado (PABA-Si). A sintese foi realizada pelo metodo hidrotermal/co-condensacao. O PABA-MCM-41 foi caracterizado usando FTIR, SAXS, adsorcao/desorcao de N2, MEV e TG. Os experimentos em batelada foram utilizados para determinar os efeitos da concentracao inicial do adsorbato, tempo de contato e temperatura. A adsorcao do benzo[a]pireno (B[a]P) alcancou o equilibrio depois de 90 min (qe = 27,2 µg g-1) e concentracoes mais altas do adsorbato foram associadas com o aumento, em ambos, da percentagem de remocao (71,0-95,7%) e no valor de qe (20,1-27,1 µg g-1). A adsorcao seguiu o modelo cinetico de pseudo-segunda ordem, e se ajustou ao modelo de isoterma de Langmuir. Foi verificado em temperaturas mais altas um aumento na taxa inicial de adsorcao e na constante cinetica. Os parâmetros termodinâmicos indicaram que o processo foi espontâneo, endotermico e com uma tendencia para desordem.

Simulating the Formation of Surfactant-Templated Mesoporous Silica Materials: A Model with Both Surfactant Self-Assembly and Silica Polymerization

We have used Monte Carlo simulations to study the formation of the MCM-41 mesoporous silica material, with a new lattice model featuring explicit representations of both silicic acid condensation and surfactant self-assembly. Inspired by experimental syntheses, we have adopted the following two-step "synthesis" during our simulations: (i) high pH and low temperature allowing the initial onset of mesostructures with long-range order; (ii) lower pH and higher temperature promoting irreversible silica condensation. During step (i), the precursor solution was found to spontaneously separate into a surfactant-silicate-rich phase in equilibrium with a solvent-rich phase. Lamellar and hexagonal ordering emerged for the surfactant-silicate-rich mesosphases under different synthesis conditions, consistent with experimental observations. Under conditions where silica polymerization can be neglected, our simulations were found to transform reversibly between hexagonal and lamellar phases by changing temperature. During step (ii), silica polymerization was simulated at lower pH using reaction ensemble Monte Carlo to treat the pH dependence of silica deprotonation equilibria. Monte Carlo simulations produced silica-surfactant mesostructures with hexagonal arrays of pores and amorphous silica walls, exhibiting Q(n) distributions in reasonable agreement with (29)Si NMR experiments on MCM-41. Compared with bulk amorphous silica, the wall domains of these simulated MCM-41 materials are characterized by even less order, larger fractions of 3- and 4-membered rings, and wider ring-size distributions.

Luminescent character of mesoporous silica with Er2O3 composite materials

Erbium oxide has been successfully incorporated into SBA-15 and different types MCM-41 mesoporous materials via thermal diffusion methods. A series of characterizations were used to characterize the prepared materials. In the prepared host–guest materials, the frameworks of the host materials were kept intact, and the guest erbium oxide mainly located inside the pores of the host materials. The host–guest composite materials showed the luminescent properties, and the luminescent intensities were excellent. Luminescence studies also revealed that the different particle size of the host materials have biggish influence to the luminescence characters. Moreover, the luminescence intensity and luminescence lifetime could be increased by the modification of the mesoporous materials surface. The better luminescent performances made these prepared materials show potential applications in optical amplification, laser systems, or medical diagnostics.

The selective catalytic reduction activity of Cu/MCM-41 catalysts prepared by using the Cu2+–MCM-41 mesoporous materials with copper ions in the framework as precursors

The Cu2+–MCM-41 mesoporous materials with different loadings of copper species in the framework have been prepared by hydrothermal method and characterized by using various physico-chemical methods combined with the selective catalytic reduction of NO by NH3. It has been shown that the particle size of metallic copper formed after hydrogen reduction is much smaller than that in the supported catalysts prepared by impregnation method, and that the SCR activity of catalyst increases obviously with the increase of Cu content to 10 wt.% because of its higher dispersion of copper metal in the mesoporous catalyst even at higher Cu loading.

The composite material of perylene bisimide dye in MCM-41 and its photophysical and photochemical properties

The mesoporous material MCM-41 was synthesized by a hydrothermal method, and perylene bisimide dye was incorporated into its channels by impregnation. The absorption, FTIR, fluorescence emission, and decay spectra of perylene bisimide dye in CHCl3 and in MCM-41 were studied to investigate the effect of the one-dimensional channel of MCM-41 on the photophysical and photochemical properties of the dye. The results indicated that the nanochannels of MCM-41 shifted the absorption and emission maxima to red and broadened the spectra, with loss of vibrational structure. The fluorescence decay curves fitted a double-exponential function and the lifetime of perylene bisimide dye in MCM-41 was prolonged. The huge surface area of the mesoporous molecular sieve MCM-41 prevented aggregation of dye molecules, which can thus be used at high concentration.

Functionalized mesoporous materials as efficient organocatalysts for the syntheses of xanthenes

Highly efficient and recyclable heterogeneous organocatalysts containing acidic functional groups such as CO2H and SO3H have been synthesized by post-synthesis modification of 2D-hexagonal mesoporous silica materials SBA-15 and MCM-41, respectively. The CO2H functionalized material is obtained via Schiff-base condensation of 3-aminopropyl grafted SBA-15 with 4-formylbenzoic acid, whereas SO3H functionalized material is prepared via partial oxidation of 3-mercaptopropyl grafted MCM-41 with dilute aqueous H2O2. These functionalized mesoporous materials have been thoroughly characterized by powder X-ray diffraction (PXRD), nitrogen adsorption/desorption studies, transmission electron microscopy (TEM) and UV visible diffuse reflectance spectroscopy. Both these materials have highly ordered 2D-hexagonal mesoporous structures with high surface areas and well-defined pore sizes. These acid functionalized materials have been used as heterogeneous catalysts for the condensation of aromatic aldehydes with 2-napthol under mild conditions in the presence or absence of a solvent affording high yields of the value added xanthenes.

Pore Size Dependent Behavior of Hydrated Ag+ Ions Confined in Mesoporous MCM-41 Materials under Synchrotron X-ray Irradiation

The behavior of hydrated Ag+ ions in a 1.5 mol dm(-3) AgNO3 aqueous solution confined in mesoporous silica MCM-41 with different pore sizes was characterized by synchrotron X-ray absorption spectroscopy. The hydrated Ag+ ions are stabilized in 4-fold coordination down to 195 K in the pores (21 Å in diameter), whereas in the larger pores (28 Å) the hydrated Ag+ ions are reduced to Ag0 to form nano clusters with the Ag-Ag interactions of 2.80 Å.

Adsorption of 2-methylbenzoic acid onto MCM-41 mesoporous material: kinetics and equilibrium studies

Ordered mesoporous molecular sieves are widely studied as alternative materials in areas where sorptive and catalytic applications are required. MCM-41 type mesoporous material was tested as sorbent of 2-methylbenzoic acid (MBA), an aromatic carboxylic acid selected as model molecule for adsorption studies on mesoporous silicas. Adsorption kinetic studies of MBA on MCM-41 type materials were carried out using ethanol solutions at different MBA concentrations. Experimental results followed Langmuir isotherm model showing large adsorption capacity (3.5 g/g). Two kinetic models, the pseudo first- and second-order, were selected to describe the adsorption process and to determine the best model fitting with the experimental data. Kinetic parameters for each kinetic equation were calculated and discussed. It was shown that the MBA adsorption process onto MCM-41 material could be described by the pseudo-second-order equation and that the MCM-41 performs as a suitable adsorbent material.

Chemical exchange and spectral coalescence in low-hydration MCM-41 studied by proton NMR

In Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) experiments, involving silica-based porous media, containing surface OH groups and water, it is generally observed that the water proton and OH group proton resonances tend to coalesce with increasing moisture content. It has been suggested that chemical exchange between protons of surface OH groups and water may not be the only mechanism producing the coalescence in the mesoporous material MCM-41. [Chem. Eur. J. 10 (2004) 5689] Here the importance of such exchange was investigated in MCM-41, hydrated to one water molecule per OH group, using low-field, static NMR relaxation techniques and high-field MAS NMR techniques. First the surface-water chemical exchange rate was estimated from two dimensional time domain NMR selective inversion recovery experiments. Second the exchange rate required to produce coalescence was estimated by modeling the exchange spectra using expected water proton NMR spectral positions and surface OH proton NMR spectral positions obtained from MAS experiments in dry MCM-41. The results suggest that the surface-water chemical exchange rate is too small to produce substantive proton NMR spectral coalescence in the MCM-41 material at this hydration level.