MCM-41 Structure Research Articles

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.

Quantification of Water and Silanol Species on Various Silicas by Coupling IR Spectroscopy and in-Situ Thermogravimetry

Five silica samples (four precipitated silicas provided by commercial suppliers and one with the MCM-41 structure) have been studied by infrared spectroscopy and by a homemade thermogravimetry-infrared spectrum (TG-IR) setup. The silanol amount, accessibility to water, and different alcohols, and the affinity to water of these various silicas were compared and quantified. TG-IR measurements allowed the precise determination of the integrated molar absorption coefficient of the (nu+delta)OH band, epsilon(nu+delta)OH=(0.16+/-0.01) cm micromol(-1). It is independent of the sample origin and the concentration of silanol groups on silicas. For the precipitated dried samples evacuated at room temperature, the silanol concentration COH varies between 3.6 and 7.0 mmol g(-1). It is 5.3 mmol g(-1) in the case of the MCM-41 sample. Exchange experiments with D2O, followed by back-exchanges with different alcohols (methanol, propan-2-ol, 2-methyl-propan-2-ol, and 3-ethyl-pentan-3-ol) have been followed by infrared spectroscopy. All of the silanols of the MCM-41 sample are accessible to water and alcohol molecules. By contrast, about 20% of the silanols in precipitated samples are not exchanged by D2O (internal silanols). Accessibility decreases with alcohol size; the main effect is relative to methanol. Taking into account the sample specific surface areas and the silanol accessibility to D2O, the surface silanol density of precipitated silicas is close to 8 OH per nm2, at maximum coverage. At variance, the silanol surface density of the MCM silica is much lower, 4 OH per nm2. The TG-IR setup has also been used to determine the amount of water adsorbed on silicas through the intensity of the deltaH2O band. It varies linearly with the concentration of adsorbed water, whatever the silica sample. The integrated molar absorption coefficient of two bands, epsilondeltaH2O=(1.53+/-0.03) cm micromol(-1) and epsilon(nu+delta)H2O=(0.22+/-0.01) cm micromol(-1), have been determined. The number of H2O molecules adsorbed per nm2 has been compared on the five samples under an equilibrium pressure of 13 hPa at room temperature. Taking into account the number of silanols accessible to D2O for each sample, the silica-water affinity has been defined by the H2O/(SiOHsurf) ratio. It is close to 0.8-0.9 for the precipitated samples but lower (0.7) in the case of the MCM one. This result is explained by the more important amount of isolated silanol groups presented by this sample.

Synthesis of MCM-41 supported amino-palladium complex and its catalytic performance for heck reaction

Using MCM-41 as the supporter, a series of MCM-41 supported amino-palladium complexes has been prepared and characterized by XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy), etc. The XRD and XPS results indicate that the Pd coordinates with the -NH2 groups on the MCM-41 surface, and the structure of MCM-41 has been not damaged. Its catalytic performance for Heck arylation of alkene with aryl iodide shows that the catalysts have high activity and stereoselectivity in 70–90°C. The product of Heck reaction is in E form. And the effect of the preparation condition of catalyst on the catalytic performance was examined.

Effect of the thermal and hydrothermal treatment on textural properties of Zr-MCM-41 mesoporous molecular sieve

Zr-containing mesoporous molecular sieves were synthesized by hydrothermal method using cetyltrimethyl ammonium bromide as a template and sodium silicate and zirconium sulfate as raw materials. The structure and morphology of the synthesized samples were characterized via various physicochemical methods, including X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, solid state nuclear magnetic resonance ( 29Si MAS-NMR) techniques, thermal gravimetric–differential scanning calorimeter (TG–DSC) and N 2 physical adsorption, respectively. The effect of the different initial ZrO 2:SiO 2 molar ratio, the different thermal treatment temperature and the different hydrothermal treatment time on textural property was investigated. The experimental results reveal that the as synthesized samples possess a typical mesoporous structure of MCM-41. On the other hand, the specific surface area and pore volume of the synthesized Zr-MCM-41 mesoporous molecular sieve decrease with the increase of the amount of zirconium incorporated in the starting material, the rise of thermal treatment temperature and the prolonging of hydrothermal treatment time, the mesoporous ordering becomes poor. Also, when the molar ratio of ZrO 2:SiO 2 in the starting material is 0.1, the mesoporous structure of the Zr-MCM-41 mesoporous molecular sieve still retains after calcination at 750 °C for 3 h or hydrothermal treatment at 100 °C for 6 d, and have specific surface areas of 423.9 and 563.9 m 2/g, respectively.

Monodispersed MCM-41 large particles by modified pseudomorphic transformation: Direct diamine functionalization and application in protein bioseparation

Direct diamine functionalization of large spherical MCM-41 (uniform particle diameter of 15 μm) was achieved via the co-condensation of pre-shaped spherical silica gel and [3-(2-aminoethyl aminopropyl)] triethoxysilane (ATMS) using a modified pseudomorphic transformation approach. The functionalized MCM-41 spheres exhibited ordered hexagonal mesostructure, narrow pore size distribution, and high-loadings of diamine group (1.785 mmol/g). The morphology of parent silica gel was well preserved during the simultaneous pseudomorphic transformation and diamine functionalization. Various characterization techniques such as thermogravimetric (TG), ultra violet–visible–near infrared (UV–vis–NIR), and solid state 29Si and 13C MAS NMR, demonstrated that the diamine groups were successfully incorporated in the spherical MCM-41 silica framework. Benzaldehyde adsorption results proved that the distribution of diamine groups was concentrated on the pore wall surface of MCM-41, and they were active and accessible for further post-treatment. The surface density of diamine groups can be easily controlled by changing the ATMS content in the initial synthesis mixture, while the order of mesoporous MCM-41 structure was maintained in appropriate extent of ATMS/SiO 2 molar ratio. This preparation method provides a new synthesis protocol to modify large particle mesoporous materials with different functional groups. Furthermore, it was demonstrated that this diamine functionalized MCM-41 large particle can be used to separate native proteins efficiently.

Synthesis, characterization and catalytic performance of Sn-MCM-48 in solvent-free Mukaiyama-type aldol condensation reactions

The influence of various synthesis variables on the physico-chemical properties of mesoporous stannosilicate molecular sieves with MCM-48 structure (Sn-MCM-48) has been investigated. Sn-MCM-48 has been used as a new heterogeneous catalyst in solvent-free Mukaiyama-type aldol reactions. Invariably, the β-hydroxy ester selectivity was found to be 100% irrespective of the conversion level. The product yield was found to increase, to reach a maximum (70%), and then to decrease with the increase in tin content.

MCM-41/ ansa-zirconocene supported catalysts: Preparation, characterization and catalytic behaviour in ethylene polymerization

An MCM-41 has been modified by grafting several zirconocene complexes to give new materials potentially active in the polymerization of α-olefins. These materials have been activated by the cocatalyst MAO, to generate the catalysts MCM-41/metallocene/MAO (metallocene = [Zr(η 5-C 5H 5) 2Cl 2] ( 1), [Zr{Me 2Si(η 5-C 5Me 4)(η 5-C 5H 4)}Cl 2] ( 2) and [Zr{Me 2Si(η 5-C 5Me 4)(η 5-C 5H 3Bu t)}Cl 2] ( 3)). The resulting functionalized ordered mesoporous silica samples ( 1– 3) were tested as catalysts in the polymerization of ethylene and compared with both the homogeneous system analogues and the functionalized silica derivatives SG/metallocene/MAO (SG = silica gel; metallocene = [Zr(η 5-C 5H 5) 2Cl 2] ( 4), [Zr{Me 2Si(η 5-C 5Me 4)(η 5-C 5H 4)}Cl 2] ( 5) and [Zr{Me 2Si(η 5-C 5Me 4)(η 5-C 5H 3Bu t)}Cl 2] ( 6)). The metallocenes 2 and 3 have been characterized by 13C-CP MAS NMR and 29Si MAS NMR spectroscopy. The structure and surface properties of MCM-41/[Zr{Me 2Si(η 5-C 5Me 4)(η 5-C 5H 4)}Cl 2] and MCM-41/[Zr{Me 2Si(η 5-C 5Me 4)(η 5-C 5H 4)}Cl 2]/MAO systems have been studied by X-ray diffractometry, nitrogen adsorption–desorption isotherms measurement and thermogravimetry. The grafting of the metallocene complexes, activation with MAO and subsequent polymerization reaction have been followed by an FT-IR “in situ” study. Scanning electron microscopy and transmission electron microscopy have been used to show the morphology of the heterogeneous catalysts as well as the resulting polyethylene obtained.

Hybrid Materials and Periodic Mesoporous Organosilicas Containing Covalently Bonded Organic Anion and Cation Featuring MCM-41 and SBA-15 Structure

We report the synthesis of a new trialkoxysilylated ionic liquid based on disilylated guanidinium and monosilylated sulfonimide species. This compound allowed the successful preparation of new periodic mesoporous organosilicas containing covalently anchored ion-pair through both organo-cationic and organo-anionic moieties which have never been reported up to now. Two classes of hybrid materials containing guanidinium-sulfonimide ion-pairs (IPs) have been synthesized. The first type of material was prepared by grafting the silylated IP onto both MCM-41-type and SBA-15-type silicas according to a surface sol-gel polymerization. The second class was synthesized following a one-pot sol-gel procedure using silylated IP and tetraethoxysilane as framework precursors. These latter materials correspond to so-called periodic mesoporous organosilicas (PMOs) and gave "organo-ionically" modified MCM-41 and SBA-15 related solids. The materials were characterized by a series of techniques including XRD, nitrogen sorption, solid-state NMR, FTIR, transmission electronic microscopy, and elemental analysis. The highest structural regularity in terms of pore size distribution and channel size homogeneity was observed for IP-PMOs possessing SBA-15-type architecture due to an enhanced trialkoxysilylated IP precursor/surfactant interaction. Solvatochromic experiments with Reichardt's dye showed good accessibility of the silica-supported ion-pair and suggested the formation of monophasic materials.

Porous Silica Nanospheres Functionalized with Phosphonic Acid as Intermediate-Temperature Proton Conductors

This paper reports the first study of developing porous silica nanospheres functionalized with phosphonic acid as intermediate-temperature (above 100 °C) proton conductors. These materials were synthesized by the co-condensation of diethylphosphatoethyltriethoxysilane (DPTS) and tetraethoxysilane using surfactant cetyltrimethylammonium bromide as a template, followed by acidification of phosphonate to phosphonic acid. With more DPTS used in the synthesis, the pore structure of the sample changes from the ordered mesoporous MCM-41 structure to the microporous structure, and the particle size simultaneously increases from ca. 80 to ca. 200 nm. The prepared silica nanospheres show promising proton conductivity above 100 °C; for example, the conductivity is as high as 3.0 × 10−4 to 0.015 S cm−1 at 130 °C when the relative humidity increases from 20 to 100%. The proton conductivity increases with an increase in the content of functionalized phosphonic acid, whereas the conductivity under low humidity condition...

Co-incorporation of MMT and MCM-41 nanomaterials used as fillers in PP composite

This study investigated the effect of co-incorporation of two different kinds of nanomaterials with different forms, layers Na-montmorillonite (Na-MMT) and particles (MCM-41), into the polymer matrix on morphology and mechanical properties of polypropylene (PP) composites. PP/Na-MMT/MCM-41 nanocomposites were prepared by melt blending. The X-ray diffraction (XRD) measurement showed that the Na-MMT layers were exfoliated and the hexagonal framework structure of MCM-41 was retained during and after the composite preparation. Scanning electron microscopy (SEM) observations revealed that the nanomaterials were well dispersed in the polymer matrix and the enhancement of the interface between the matrix and fillers were obtained. The results of mechanical tests showed that at same nanomaterial loading, the co-incorporation of Na-MMT and MCM-41 into the PP matrix gave rise to much better enhanced effects than incorporating either Na-MMT or MCM-41 particles separately due to different interfacial structure between the fillers and the matrix.

Is There Any Microporosity in Ordered Mesoporous Silicas?

The porous structure of nanostructured silicas MCM-41 and SBA-15 has been characterized using N2 adsorption at 77 K, before and after n-nonane preadsorption, together with immersion calorimetry into liquids of different molecular dimensions. Selective blocking of the microporosity with n-nonane proves experimentally that MCM-41 is exclusively mesoporous while SBA-15 exhibits both micro- and mesopores. Additionally, N2 adsorption experiments on the preadsorbed samples show that the microporosity on SBA-15 is located in intrawall positions, the micropore volume accounting for only approximately 7-8 % of the total pore volume. Calorimetric measurements into n-hexane (0.43 nm), 2-methylpentane (0.49 nm), and 2,2-dimethylbutane (0.56 nm) estimate the size of these micropores to be < or = 0.56 nm.

The structural comparison between Al-MCM-41 and B-MCM-41

A series of mesoporous aluminosilicate and borosilicate molecular sieves with the MCM-41 structure have been synthesized with different SiO2/Al2O3 or SiO2/B2O3 mass ratios of 5, 10, 25, 50, 70 and 150. The samples were synthesized using the direct method with a duration of 48 h. As silica source colloidal silica (ludox 40%, Prolabo), as aluminium source sodium aluminates and boric acid as the boron source were used in these syntheses. All samples were characterized by X-ray diffraction (XRD), ATR-FT-IR, N2 gassorption and elemental analysis by electron microscopy. XRD revealed that the characteristic MCM-41 structure is obtained for both mass ratios greater than 10. B-MCM-41 gives a better organization of the structure than Al-MCM-41. The B substitution in MCM-41 gives a tetrahedral configuration as proven by ATR-FT-IR. The pore diameter is very similar in both samples.

Sol–Gel Assisted Preparation of Chromia–Silica Catalysts for Non-Oxidative Dehydrogenation of Propane

Preparation of continuous silica gel in the presence of dissolved Cr(NO3)3 leads to a hard high surface area (710 m2/g) microporous xerogel. Formation of the gel in the pore structure of mesoporous Pore-Expanded MCM-41 (PE-MCM-41) and macroporous commercial Cab–O–Sil silica results in retention of the mesoporous structure in the case of PE-MCM-41, and the formation of a powder with a broad pore size distribution in the case of Cab–O–Sil silica. Comparison of the catalytic activities in non-oxidative dehydrogenation of propane revealed a linear correlation of the initial conversion with the surface area for all three samples. The sample prepared from PE-MCM-41 through a sol–gel assisted procedure was the most active, particularly with respect to the catalysts prepared by simple wet impregnation with chromium nitrate.

Synthesis of cerium-doped MCM-48 molecular sieves and its catalytic performance for selective oxidation of cyclohexane

Cerium-doped MCM-48 molecular sieves were synthesized hydrothermally and characterized by X-ray diffraction, nitrogen adsorption, transmission electron microscope, FT-IR spectroscopy, UV-visible spectroscopy, and Raman spectroscopy. The results showed that all the samples held the structure of MCM-48, and Ce could enter the framework of MCM-48. However, when Ce/Si molar ratio in the samples was high (0.04 or 0.059), there were CeO 2 crystallites as secondary phase in the extraframework of MCM-48. Ce-doped MCM-48 was a very efficient catalyst for the oxidation of cyclohexane in a solvent-free system with oxygen as an oxidant. In the conditions of 0.5 MPa O 2 and 413 K for 5 h, the conversion of cyclohexane was 8.1% over Ce-MCM-48-0.02, the total selectivity of cyclohexanol and cyclohaxnone was 98.7%. With an increase of Ce content, the conversion of cyclohexane and the selectivity to cyclohexanol decreased somewhat, but the selectivity to cyclohexanone increased.

Direct Imaging of Surface Topology and Pore System of Ordered Mesoporous Silica (MCM-41, SBA-15, and KIT-6) and Nanocast Metal Oxides by High Resolution Scanning Electron Microscopy

We report here a detailed study on the surface topology of well-known ordered mesoporous silica (SBA-15, MCM-41, and KIT-6) and a series of nanocast Co 3O 4, Co 3O 4/CoFe 2O 4 composites by high resolution scanning electron microscopy (HR-SEM). Images of the MCM-41 structure were obtained at a resolution of the pore size, as well as a real space image of the gyroid silica surface of KIT-6 for two different aging temperatures, clearly revealing the differences of the aging procedures. By using the low voltage HR-SEM technique with extremely high resolution, we could very clearly show the influence of the template properties on the structure of the nanocast metal oxides.

Near-infrared luminescent mesoporous MCM-41 materials covalently bonded with ternary thulium complexes

Two β-diketones 4,4,4-trifluoro-1-2-thenoyl-1,3-butanedione (Htta) and 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione (Htfnb), which contain trifluoroalkyl chain, were selected as the main sensitizer for synthesizing Tm(L) 3phen (L = tta, tfnb) complexes. The two near-infrared (NIR) luminescent thulium complexes have been covalently bonded to the ordered mesoporous material MCM-41 via a functionalized 1,10-phenanthroline (phen) group 5-( N, N-bis-3-(triethoxysilyl)propyl)ureyl-1,10-phenanthroline (phen-Si) [The resultant mesoporous materials are denoted as Tm(L) 3phen–MCM-41 (L = tta, tfnb)]. The Tm(L) 3phen–MCM-41 (L = tta, tfnb) mesoporous materials were characterized by small-angle X-ray diffraction (XRD) and N 2 adsorption/desorption, and they show characteristic mesoporous structure of MCM-41. Luminescence spectra of the Tm(L) 3phen–MCM-41 (L = tta, tfnb) mesoporous materials were recorded and the corresponding luminescence decay curves were obtained. After ligand-mediated excitation, the emission spectra of the Tm(L) 3phen–MCM-41 (L = tta, tfnb) mesoporous materials show the characteristic NIR-luminescence of the Tm 3+ ion. The full width at half maximum (fwhm) of the 1474-nm emission band are 96 and 100 nm for Tm(tta) 3phen–MCM-41 and Tm(tfnb) 3phen–MCM-41, respectively. The good luminescent performances enable these NIR-luminescent mesoporous materials to have potential applications in optical amplification [broadening amplification band from C band (1530–1560 nm) to S + band (1450–1500 nm)]. Furthermore, the comparison of the luminescence behavior for Tm(tta) 3phen–MCM-41 and Tm(tfnb) 3phen–MCM-41 mesoporous materials was investigated. It shows that Tm(tfnb) 3phen–MCM-41 is somewhat superior to Tm(tta) 3phen–MCM-41 as optical amplifier.

Host (nanodimensional pores of mesoporous material)–guest (semiconductor nanoparticles) nanocomposite materials

An aluminosilicate with the MCM-41 structure (AlMCM-41) was used as a host for the synthesis of cobalt sulfide nanoparticles. Cobalt sulfide nanoparticles were introduced in host by ion exchange and hydrothermal methods. Products (CoSAlMCM-41) were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), EDX, IR, BET and UV–vis spectroscopy. The results show that CoS nanoparticles encapsulated into channels of AlMCM-41 material by hydrothermal synthesis and they grow outside the mesopore AlMCM-41 matrix by ion-exchange methods. Absorption peaks at higher energy than the fundamental absorption edge of bulk CoS indicate quantum confinement effect in nanoparticles as a consequence of their small size. The absorption spectra show that the optical band gap for CoS nanoparticles by hydrothermal and ion-exchange methods are 3.73 and 4.89, respectively.

The role of different parameters of synthesis in the final structure of Ti-containing mesoporous materials

Ti-containing mesoporous materials have been prepared by hydrothermal synthesis at 373 K and compared to pure siliceous MCM-41 synthesized in the same conditions. A detailed and correlative study about the effect of different synthesis parameters on the physicochemical properties of the material has been carried out. All the samples showed typical XRD patterns of a kind MCM-41 structure. It seems that the synthesis time and the surfactant chain length are critical variables to obtain good structures. Mesoporous structure allowed the incorporation of different degrees of Ti loading, although a lower degree of ordering was observed with the increase of metal content above 1%. Moreover, a high incorporation of Ti into the structure seems responsible for the development of a secondary mesoporosity confirmed by TEM and associated with a pronounced hysteresis loop in the N 2 isotherm. DRUVA-Vis and XPS studies revealed that the Ti species are mainly found isolated and tetrahedral coordinated into the framework. The superego-Ti(IV) species generated by the interaction of Ti-MCM-41 with aqueous H 2O 2 have been studied by EPR spectroscopy and correlated to DRUVA-Vis and XPS measurements.

Preparation, characterization and optical properties of lanthanum-(nanometer MCM-41) composite material

Nanometer MCM-41 molecular sieve was prepared under a base condition by using cetyltrimethylammonium bromide as template and tetraethyl orthosilicate as silica source by means of hydrothermal method. Lanthanum(III) was incorporated into the nanometer MCM-41 by a liquid phase grafting method. The prepared nanocomposite materials were characterized by means of powder X-ray diffraction, spectrophotometric anaylsis, Fourier transform infrared spectroscopy, low temperature nitrogen adsorption-desorption technique, solid diffuse reflectance absorption spectra and luminescence. The powder X-ray diffraction studies show that the nanometer MCM-41 molecular sieve is successfully prepared. The highly ordered mesoporous two-dimensional hexagonal channel structure and framework of the support MCM-41 is retained intact in the prepared composite material La-(nanometer MCM-41). The spectrophotometric anaylsis indicates that lanthanum exists in the prepared nanocomposite materials. The Fourier transform infrared spectra indicate that the framework of the MCM-41 molecular sieve still remains in the prepared nanocomposite materials and some framework vibration peaks show blue shifts relative to those of the MCM-41 molecular sieve. The low temperature nitrogen adsorption-desorption indicates that the guest locates in the channel of the molecular sieve. Compared with bulk lanthanum oxide, the guest in the channel of the molecular sieve has smaller particle size and shows a significant blue shift of optical absorption band in solid diffuse reflectance absorption spectra. The observed blue shift in the solid state diffuse reflectance absorption spectra of the lanthanum-(nanometer MCM-41) sample show the obvious stereoscopic confinement effect of the channel of the host on the guest, which further indicates the successful encapsulation of the guest in the host. The La-(nanometer MCM-41) sample shows luminescence.

H2S photodegradation by TiO2/M-MCM-41 (M = Cr or Ce): Deactivation and by-product generation under UV-A and visible light

M-MCM-41 molecular sieves (M=Ce or Cr) were prepared by a hydrothermal method and impregnated with TiO2. The materials were characterized by XRD, N2 adsorption–desorption, DRS and XPS. Their potential application to photooxidize H2S in a wet gas stream was tested in a continuous flow reactor operating at a flow rate of 110mLmin−1 at 50% relative humidity and using 30ppmv of the pollutant. The photocatalytic efficiency using UV-A and visible light was compared to the activity of TiO2/MCM-41 without heteroatoms incorporated into the MCM-41 structure. It was found that the incorporation of Ce did not improve the performance of TiO2/MCM-41, but Cr-containing samples presented higher initial efficiency and were able to photooxidize H2S without formation of SO2 as a by-product, in contrast to the other prepared samples and to Degussa P-25 TiO2. Moreover, no other gaseous by-product was detected. The isomorphic incorporation of Cr into the structure of MCM-41 followed by TiO2 incorporation produced photocatalysts that presented good adsorption capacity and were much more active under visible light than under UV-light. This performance represents an important advantage for solar applications. Their photoactivity depended on the concentration of chromium; the highest efficiency was attained with samples with a Si/Cr ratio of 50. Finally, deactivation was observed as a consequence of sulfate accumulation on the surface of the catalyst and reduction of Cr6+.