Mesoporous Molecular Sieve MCM-41 Research Articles

Synthesis of multi-wall carbon nanotubes by the pyrolysis of ethanol on Fe/MCM-41 mesoporous molecular sieves

Ordered hexagonal arrangement MCM-41 mesoporous molecular sieves were synthesized by the traditional hydrothermal method, and Fe-loaded MCM-41 mesoporous molecular sieves (Fe/MCM-41) were prepared by the wet impregnation method. Their mesoporous structures were testified by X-ray diffraction (XRD) and the N 2 physical adsorption technique. Carbon nanotubes (CNTs) were synthesized by the chemical vapor deposition (CVD) method via the pyrolysis of ethanol at atmospheric pressure using Fe/MCM-41 as a catalytic template. The effect of different reaction temperatures ranging from 600 to 800 ∘C on the formation of CNTs was investigated. The resulting carbon materials were characterized by various physicochemical techniques such as transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. The results show that multi-wall carbon nanotubes (MWCNTs) with an internal diameter of ca. 7.7 nm and an external diameter of ca. 16.9 nm were successfully obtained by the pyrolysis of ethanol at 800 ∘C utilizing Fe/MCM-41 as a catalytic template.

Immobilization of 5,10,15,20-tetrakis-(2-fluorophenyl)porphyrin into MCM-41 and NaY: Routes toward photodegradation of pesticides

NaY zeolite and MCM-41 mesoporous molecular sieve were used as supports for immobilization of 5,10,15,20-tetrakis-(2-fluorophenyl)porphyrin (TFPP) using adsorption and ship-in-the-bottle routes involving the nitrobenzene method. The materials obtained were characterized by thermogravimetry/differential thermal analysis (TG/DTA), nitrogen adsorption, UV–vis absorption, diffuse reflectance (DRS), and luminescence spectroscopy. Although the porphyrin could easily be synthesized inside MCM-41 pores using the ship-in-the-bottle route, no significant porphyrin was formed in the smaller supercages of NaY zeolite, since the reaction stops at the dipyrrolylmethene intermediate (FDPM). Promising preliminary studies were made in the photodegradation of the pesticides, 2,3,5-trimethylphenol (TMP) and mecoprop (MCPP), using as catalyst TFPP encapsulated in mesoporous MCM-41 material. The 2-hydroxy-methyl-hydroquinone and 4-chloro-2-methylphenol were identified as the main degradation products of MCPP. The encapsulated system resulting from the TFPP template synthesis shows significantly enhanced performance when compared with adsorbed porphyrin in both supports.

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.

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.

MCM-41 supported nickel-based bimetallic catalysts with superior stability during carbon dioxide reforming of methane: Effect of strong metal–support interaction

Nickel-based bimetallic catalysts supported on MCM-41 mesoporous molecular sieves (Ni–Ti-, Ni–Mn-, and Ni–Zr–MCM-41) were prepared by direct hydrothermal synthesis. The catalytic properties were tested in methane reforming with CO 2. All Zr-promoted catalysts exhibited comparable or enhanced initial catalytic activity as compared to Ni–MCM-41. Adding Zr 4+ remarkably improved the long-term stability, whereas decreased lower initial activity and stability were observed for Ti- and Mn-modified catalysts. The addition of Zr 4+ enhanced the structural stability and the dispersion of active Ni sites. The strong anchoring effect of Zr 4+ and the partial activation of CO 2 by Zr 4+ contributed to the high catalytic activity and long-term stability. On the contrary, the decoration of Ni clusters with TiO x and MnO x species on Ni–Ti and Ni–Mn catalysts hindered the accessibility of Ni-active centers, thus decreasing their catalytic performance. The partial transformation of amorphous silica matrix into quartz and/or tridymite phases over Ni–Mn, Ni–Ti, and Ni–MCM-41 catalysts also played a negative role on their catalytic stability.

Effect of the Si/Ce molar ratio on the textural properties of rare earth element cerium incorporated mesoporous molecular sieves obtained room temperature

Rare earth Ce-incorporated MCM-41 mesoporous molecular sieves (CeMCM-41) were synthesized via a direct and nonhydrothermal method at room temperature from sodium silicate and ammonium cerium (IV) nitrate as raw materials. Cetyltrimethyl ammonium bromide (CTAB) was used as a template. The resultant samples were characterized by means of powder X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance ultraviolet–visible spectroscopy (UV–vis) and N 2 physical adsorption, respectively. The effect of the Si/Ce molar ratio on the crystalline structure and textural properties of CeMCM-41 was also investigated. The experimental results show that ordered CeMCM-41 mesoporous molecular sieves were successfully synthesized at room temperature and the resultant mesoporous materials have specific surface areas in the range of 594–1369 m 2/g and average pore sizes in the range of ca. 2.5–2.8 nm. It has been found that the structural properties are strongly related to the amounts of cerium incorporation. When the cerium content increased in the samples, the intensity of the peak (1 0 0) was gradually reduced, and the surface area and structural regularity were diminished.

Immobilization of bis(imino)pyridine iron complexes onto mesoporous molecular sieves and their catalytic performance in ethylene oligomerization

Abstract Bis(imino)pyridine iron complexes were supported on MAO-treated mesoporous molecular sieves MCM-41 and SBA-15. The effects of reaction temperature and Al/Fe mole ratio on ethylene oligomerization were investigated in detail. The supported complexes, upon activation with MAO, exhibited good catalytic performance towards ethylene oligomerization and formed linear α-olefins at high reaction temperatures. MCM-41 with relatively narrow pore size tended to produce more lower molar mass α-olefins possibly due to more remarkable confinement effects.

Synthesis of hydrothermally stable MCM-48 mesoporous molecular sieve at low cost of CTAB surfactant

The hydrothermally stable MCM-48 mesoporous molecular sieve was successfully prepared at extremely low cost of cetyltrimethylammonium bromide (CTAB) by carefully adjusting the synthesis conditions. The increasing of the crystallization temperature from 373 K to 423 K can dramatically reduce the CTAB surfactant amount for the preparation of MCM-48 from 0.65 to 0.1 of the CTAB/Si ratio. The effect of increasing crystallization temperature on the formation process of MCM-48 at low CTAB cost was carefully studied. The influences of OH −/Si ratio and fluoride addition to the structure stability of the MCM-48 material synthesized at CTAB/Si = 0.1 and 423 K were systematically studied by XRD patterns. Moreover, the combination of increasing crystallization temperature and adding small amount of fluoride ions can considerably improve the structure stability of MCM-48 when reducing the CTAB cost.

Carbon dioxide reforming of methane to synthesis gas over Ni-MCM-41 catalysts

A series of nickel incorporated MCM-41 mesoporous molecular sieves (Ni-MCM-41) were prepared by direct hydrothermal synthesis. Nickel nitrate was used as the Ni precursor. The catalytic properties of the Ni-MCM-41 were studied for the reforming of methane with carbon dioxide. The catalysts were carefully characterized by X-ray diffraction (XRD), N 2 physisorption, H 2 temperature-programmed reduction (TPR), H 2 chemisorption, thermogravimetry, and Raman spectra. The results indicated that the presence of a suitable amount of nickel in Ni-MCM-41 was beneficial for maintaining high catalytic activity and long-term stability. The improved catalytic performance was suggested to closely associate with both the amount of active centers on the pore wall surface and the stabilized dispersion of these active sites by the silica matrix and/or the surrounding unreduced nickel ions. This anchoring effect facilitated the formation of the active Ni nano-clusters with high dispersion under reaction conditions. Hence the reforming reaction is favored and the carbon formation is suppressed. Two types of carbon species: active carbon and graphite were produced over the spent catalysts. The Ni-MCM-41 catalysts provided good catalytic activity, high stability and reasonable CO/H 2 ratios in the product. Thus, the Ni-MCM-41 catalyst prepared by the direct hydrothermal synthesis promised a novel and stable catalyst candidate for CO 2 reforming of CH 4.

Correlation between deuterium NMR spectral components and MCM-41 pore surface hydration sites

The elucidation of water molecule dynamics on surfaces and in confined geometry using NMR techniques is facilitated by knowledge about the different hydration sites involved and about the correlation between NMR spectral features and such sites. In the mesoporous molecular sieve MCM-41 substantial information exists about the former, however, satisfactory information about the latter is still lacking for this material. In the present investigation proton and deuteron NMR, MAS, and CPMAS techniques are used to establish a definitive assignment of deuterium spectral features to water at single and hydrogen-bonded pore surface hydroxyl group binding sites in MCM-41.

MCM-41 prepared with ionic liquid and cethytrimethylammonium bromide as co-templates

The mesoporous molecular sieves MCM-41 were prepared using room temperature ionic liquid (RTIL) synthesized in laboratory and cethytrimethylammonium bromide (CTAB) as compound templates for the first time. They were prepared under low aging temperature and short aging time. Via characterizing by XRD and nitrogen adsorption instrument, MCM-41 synthesized by this new method exhibited good crystal structure and narrow pore distribution. The following preparatory conditions was optimal: the molar ratio of RTIL to CTAB was 1.0:1.0, aging at 80 °C, for 40 h and calcined at 540 °C. It is found that the acidified MCM-41 improves its activity as catalyst over the unmodified ones.

Dielectric response of water confined in metal–organic frameworks

Dielectric response of water confined in metal–organic frameworks was investigated in broad temperature range from 140 to 410 K and from 20 Hz to 1 MHz using a capacitance bridge. Several dispersion regions of characteristic shape were found, caused by freezing–melting of adsorbed water molecules, which disappear after a prolonged heating at 410 K. Temperature dependencies of relaxation time of confined water molecules were obtained and are compared to those of water confined in MCM-41 mesoporous molecular sieves.

Liquid-phase oxidation of benzene and phenol on MCM-41 mesoporous molecular sieves modified with iron and cobalt compounds

Nanostructured (I) Fe2O3 and Co3O4 stabilized in the mesopores of an MCM-41 sieve and immobilized (II) FeCl2, Fe(acac)3, and FePc on the surface of an MCM-41 sieve functionalized with 3-aminopropyltriethoxysilane (3-APTES) were synthesized and examined. The materials were characterized by elemental analysis, H2 -TPR, X-ray diffraction analysis, IR and electronic absorption spectroscopy, as well as by low-temperature N2 adsorption. The catalytic activity was evaluated in the reaction of liquid-phase oxidation of benzene and phenol with hydrogen peroxide. Catalysts I showed a low activity in benzene oxidation, whereas catalysts II were active in the oxidation of phenol.

MCM-41 mesoporous molecular sieves modified with a base or a palladium-containing ionic liquid as catalysts for certain organic synthesis reactions

MCM-41 molecular sieves modified with γ-aminopropyltriethoxysilane, as well as an imidazole ionic liquid with palladium chloride, exhibit high activity in the liquid-phase Knoevenagel and Heck reactions.

Direct synthesis of vanadium substituted mesoporous MCM-41 molecular sieves: a systematic study for the growth of SWNTs

Vanadium incorporated MCM-41 molecular sieves with various Si/V ratios (25, 50, 75 and 100) were synthesized hydrothermally and their mesoporous structure were confirmed by various physicochemical techniques such as XRD, N2 sorption studies and DRs UV–vis Spectroscopy. The catalytic activity of these molecular sieves was tested for the production of carbon nanotubes (CNTs) through acetylene decomposition at atmospheric pressure utilising catalytic chemical vapour deposition (CCVD) technique. In order to achieve the high carbon yield, the decomposition of hydrocarbon was carried out at different temperatures ranging from 650 to 850 °C. The effect of other reaction parameters like flow rate of hydrocarbon and V-MCM-41 with various Si/V ratio are also investigated. Using our optimised conditions for the system, the CNTs were selectively synthesised with a less amount of amorphous carbon, which were then purified and characterised by TGA, SEM, TEM and Raman spectroscopy.

Catalytic cracking of polypropylene into liquid hydrocarbons over Zr and Mo modified MCM-41 mesoporous molecular sieve

Abstract Catalytic cracking of polypropylene (PP) has been investigated over MCM-41 modified by Zr and Mo. The relationship among structure, acidity and catalytic activity of Zr–Mo-MCM-41 was studied. The results showed that Zr–Mo-MCM-41 exhibited high activity for the cracking of PP and good selectivity for producing liquid hydrocarbons of higher carbon numbers. The results were compared with those obtained over HZSM-5, SiO 2 –Al 2 O 3 and other MCM-41 mesoporous molecular sieves. Moreover, the effect of different Zr sources on the reaction was examined.

Catalytic activity of Fe, Co and Fe-Co-MCM-41 for the growth of carbon nanotubes by chemical vapour deposition method

Iron, cobalt and a mixture of iron and cobalt incorporated mesoporous MCM-41 molecular sieves were synthesised by hydrothermal method and used to investigate the rules governing their nanotube producing activity. The catalysts were characterised by XRD and N 2 sorption studies. The effect of the catalysts has been investigated for the production of carbon nanotubes at an optimised temperature 750 °C with flow rate of N 2 and C 2H 2 is 140 and 60 ml/min, respectively for a reaction time 10 min. Fe-Co-MCM-41 catalyst was selective for carbon nanotubes with low amount of amorphous carbon with increase in single-walled carbon nanotubes (SWNTs) yield at 750 °C. Formation of nanotubes was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. Transmission electron microscope and Raman spectrum was used to follow the quality and nature of carbon nanotubes formed and the graphitic layers and disordered band, which shows the clear evidence for the formation of SWNTs, respectively. The result propose that the diameter of the nanotubes in the range of 0.78–1.35 nm. Using our optimised conditions for this system, Fe-Co-MCM-41 showed the best results for selective SWNTs with high yield when compared with Fe-MCM-41 and Co-MCM-41.

Use of TiO 2/Cr-MCM-41 molecular sieve irradiated with visible light for the degradation of thiophene in the gas phase

Photocatalytic processes using TiO 2 and UV radiation to eliminate pollutants are not yet suitable for industrial facilities due to their high consumption of energy. Transition metals incorporated onto mesoporous MCM-41 molecular sieves impregnated with TiO 2 constitute an alternative that allows the use of solar light. In this study, Cr-substituted MCM-41 were synthesized (Si/Cr = 100, 50 and ∞) and impregnated with TiO 2 (10 and 20 wt.%). Raman results showed the formation of anatase. Electronic spectroscopy and EPR exposed the formation of trivalent chromium after impregnation with TiO 2, which is related to a Cr–TiO 2 interaction. The synthesized photocatalysts, as well as TiO 2 P25, were tested in the degradation of thiophene in gaseous phase. A test with UV lamp showed 100% of conversion for 20%TiO 2/Cr-MCM-41(100) and exceeded the activity of TiO 2 P25, probably due to the higher dispersion of TiO 2 on the surface of the molecular sieve. During tests using visible light and 20%TiO 2/Cr-MCM-41(50) higher conversions than those of 20%TiO 2/Cr-MCM-41(100) and TiO 2 P25 were observed. These results indicate that chromium concentration is a key factor influencing the photocatalytic activity under visible light.