MCM-41 Molecular Sieves Research Articles

Mesoporous silica MCM-48 molecular sieve modified with SnCl 2 in alkaline medium for selective oxidation of alcohol

Tin modified mesoporous silica MCM-48 with various Si/Sn ratios were synthesized under alkaline media by post-synthesis modification using rice husk ash as Si precursor and SnCl 2 as tin source. Physicochemical information of the materials was obtained by XRD, N 2-physisorption, FESEM, UV–VIS diffuse reflectance and FTIR spectroscopies. The tin modified MCM-48 samples were selective in the oxidation of benzyl alcohol to benzaldehyde by using tert-butyl hydroperoxide aqueous solution as oxidant. The catalytic activity can be correlated with the strong Lewis acidity generated by the presence of tin species in Si-MCM-48. The re-usability of tin modified MCM-48 catalysts and the effect of substrate to oxidant ratio on the catalytic activity are discussed.

Photocatalytic degradation of methyl thionine chloride in aqueous solution over nanometer (CdS/TiO2)/MCM-41

(CdS/TiO2)/MCM-41 loaded nanometer photocatalyst was prepared by the sol-gel method and dipping process, the photocatalytic degradation of methyl thionine chloride in water was investigated by using the photocatalyst. The experimental results show that the optimum concentration of CdS over TiO2 was 3% (molar ratio), the photocatalytic activity was enhanced when making TiO2 the anatase phase with a rise of the roasting temperature, and the carrier, mesoporous molecular sieve MCM-41, was beneficial to improving the photocatalytic activity of TiO2 for photocatalytic degradation of methyl thionine chloride. The morphology and the crystalline phase of the photocatalyst were discussed by means of XRD and SEM techniques, and the reaction mechanism of catalytic properties was also discussed.

Effective Synthesis of Single-Walled Carbon Nanotubes Using Ni−MCM-41 Catalytic Template through Chemical Vapor Deposition Method

Mesoporous Ni−MCM-41 molecular sieves with various Si/Ni ratios 25, 50, 75, and 100 were synthesized hydrothermally, and their mesoporous structure was confirmed by various physicochemical techniques such as X-ray diffraction (XRD), N2 adsorption studies, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The catalytic activity of these molecular sieves was tested and optimized for the maximum yield of carbon nanotubes (CNTs) in the vapor phase at various temperatures ranging from 650 to 850 °C. Ni−MCM-41 (100) was found to consist of the optimum amount of metal to form large metallic clusters leading to higher carbon deposits. The optimum reaction temperature for high carbon deposits was found to be at 750 °C. The maximum percentage of carbon deposit increased from 9.33 to 71.01% when the flow rate was increased from 20 to 60 mL/min. The purified CNTs were characterized by XRD, SEM, TEM, and Raman spectroscopy techniques. The analysis showed that these CNTs have larger diameters and good graphitization. The morphology of CNTs studied by TEM clearly showed the formation of carbon nanotubes with uniform diameter in the range of 25−30 nm.

Esterification of alkyl acids with alkanols over MCM-41 molecular sieves: Influence of hydrophobic surface on condensation reaction

The Al-MCM-41 mesoporous materials with Si/Al ratios 29, 52, 74 and 110 were synthesized by hydrothermal method and characterized by powder X-ray diffraction (XRD), nitrogen adsorption–desorption measurements (BET), 29Si-MAS-NMR, 27Al-MAS-NMR, DRIFT, SEM and TGA–DTG techniques. The XRD studies indicated ordered hexagonal structure for all the samples. The specific surface area, pore volume, and pore size distribution of the samples were comparable to mesoporous molecular sieves. The catalytic activity of these materials was tested for the esterification of acetic acid (AA) with 1-hexanol (HeOH), 2-ethyl-1-hexanol (2E-1HOH), isoamyl alcohol (IAOH), and propionic acid (PA) with isoamyl alcohol under autogenous conditions. The effects of temperature from 75 to 150°C, initial molar feed ratios, acid:alcohol, 1:1, 1:2, 2:1, 3:2 and 5:2, amount of catalyst and the reaction time were also investigated. The yield of the product ester was observed with higher for the feed ratio 5:2. Under the experimental conditions, Al-MCM-41 (110) a hydrophobic material showed higher alcohol conversion with acetic acid at 125°C than the other catalysts. The conversion with respect to the alcohols followed the order HeOH (88.4%)>IAOH (87.7%)>2E-1HOH (84.4%). All the product esters showed selectivity close to 100%. The hydrophobic properties of the catalysts were suggested to play important role in the esterification reaction.

Enrichment of Phosphopeptides by Fe3+-Immobilized Mesoporous Nanoparticles of MCM-41 for MALDI and Nano-LC−MS/MS Analysis

Fe3+-immobilized mesoporous molecular sieves MCM-41 with particle size of ca. 600 nm and pore size of ca. 3 nm is synthesized and applied to selectively trap and separate phosphopeptides from tryptic digest of proteins. For the capture of phosphopeptides, typically 10 microL of tryptic digest solution was first diluted to 1 mL by solution of ACN/0.1% TFA (50:50, v/v) and incubated with 10 microL of 0.1% acetic acid dispersed Fe3+-immobilized MCM-41 for 1 h under vibration. Fe3+-immobilized MCM-41 with trapped phosphopeptides was separated by centrifugation. The deposition was first washed with a volume of 300 microL of solution containing 100 mM NaCl in ACN/0.1% TFA (50:50, v/v) and followed by a volume of 300 microL of solution of 0.1% acetic acid to remove nonspecifically bound peptides. The nanoparticles with trapped phosphopeptides are mixed with 2,5-dihydroxybenzoic acid (2,5-DHB) and deposited onto the target for analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). It was found that phosphopeptides from tryptic digest of alpha-casein and beta-casein are effectively and specifically trapped on Fe3+-immobilized MCM-41 with few peptides nonspecifically adsorbed. After the extraction by Fe3+-immobilized MCM-41, the suppression to the detection of phosphopeptides caused by abundant nonphosphopeptides from tryptic digest is effectively eliminated, and the detection of phosphopeptides by MALDI is greatly enhanced with the value of signal-to-noise (S/N) increased by more than an order of magnitude. It is demonstrated that the mechanism of the adsorption of phosphopeptides on Fe3+-immobilized MCM-41 is based on the interaction between the Fe3+ and the phosphate group. Finally, Fe3+-immobilized MCM-41 is applied to extract phosphopeptides from tryptic digest of the lysate of mouse liver for phosphoproteome analysis by nano-LC-MS/MS.

Grafting of palladium nanoparticles onto mesoporous molecular sieve MCM-41: Heterogeneous catalysts for the formation of an N-substituted pyrrol

Palladium nanoparticles, obtained by thermochemical reduction of palladium(II) acetate in propylene carbonate or in tetrahydrofuran with added tetrabutylammonium acetate (Bu 4NOAc), were deposited onto mesoporous molecular sieve MCM-41 (spontaneously or after solvent change) to give novel supported metal catalysts, which were characterized by chemical analysis, powder X-ray diffraction, nitrogen adsorption-desorption isotherms and high-resolution transmission electron microscopy (HR TEM). The materials, together with 10% Pd/C reference were utilized as catalysts in the condensation reaction of 2-aminoethanol with cis-butene-1,4-diol to afford N-(2-hydroxyethyl)pyrrol. Both supported catalysts showed significantly higher conversions that Pd/C, the one prepared in the presence of Bu 4NOAc being the most active. Catalysts isolated after the reaction and used repeatedly showed lower activity than fresh ones. This apparently reflects partial metal leaching from the solid support and aggregation of the metal particles that were demonstrated by catalytic tests and HR TEM measurements, respectively.

Photo-assisted synthesis of V and Ti-containing MCM-41 under UV light irradiation and their reactivity for the photooxidation of propane

V and Ti-containing mesoporous molecular sieves MCM-41 were prepared using a photo-assisted synthesis method with UV light irradiation of the starting solutions at room temperature within a short synthesis time. The prepared V-MCM-41 showed high reactivity for the photocatalytic partial oxidation of propane into acetone. This reaction was enhanced on the V–Ti-MCM-41 catalyst with a higher acetone yield and selectivity than for V-MCM-41. After quenching, the recovery of the photoluminescence of V–Ti-MCM-41 proceeded more efficiently than that of V-MCM-41 by evacuation at 295 K. These results suggest that the excited state of the V-oxide moieties in V–Ti-MCM-41 interacts more weakly with the O 2 molecules, leading to the suppression of further oxidation of the photo-formed acetone into CO 2.

Studies on MCM-41: Effect of sulfate on nitration of phenol

The mesoporous molecular sieve MCM-41 was synthesized by sol–gel method using tetraethyl orthosilicate (TEOS), cetyl trimethyl ammonium bromide (CTAB), aqueous NH 3 and water. A series of sulfate modified MCM-41 was prepared by incipient wetness impregnation method using H 2SO 4 as sulfatising agent. The samples were characterized by BET surface area, X-ray diffraction, FT-IR and TG–DTA. The catalytic activity of the samples was evaluated for nitration of phenol with nitric acid in dichloro ethane (DCE) medium, at room temperature. The effect of reaction parameters, i.e. time, concentration of nitric acid and phenol/nitric acid ratio were also investigated. Modification with sulfate opened new opportunities to generate active Brønsted and Lewis acid sites in the stabilized nanostructure MCM-41. Among the catalysts screened, 4 wt.% sulfated MCM-41 showed maximum activity (93%), with 90% selectivity towards ortho-nitrophenol.

Characterization and catalytic properties of nanosized cobaltate particles prepared by in situ synthesis inside mesoporous molecular sieves

Bulk lanthanum cobaltate (LaCoO 3) with perovskite-like structure and LaCoO x supported onto the mesoporous MCM-41 molecular sieve were synthesized by the conventional citrate method. The prepared samples were characterized by XRD, nitrogen BET measurements, H 2-temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), XAFS and SEM-energy-dispersive X-ray (EDX) techniques. The turnover frequency of the supported cobaltate in methanol oxidation is two orders of magnitude larger than that of the bulk perovskite material. Based on the characterization results, it is concluded that the supported cobaltate does not form species of LaCoO 3 short-range order in MCM-41. The high activity is related to a highly disordered, oxygen-deficient Co oxide phase, which is probably stabilized by the La ions present.

Metathesis of 1-octene over MoO 3 supported on mesoporous molecular sieves: The influence of the support architecture

New types of heterogeneous catalysts for alkene metathesis based on molybdenum oxide supported on mesoporous molecular sieves MCM-41, MCM-48 and SBA-15 were developed. These new systems represent inexpensive, easy-to-prepare and highly active and selective heterogeneous catalysts for metathesis of linear alkenes applicable under mild reaction conditions without the necessity of solvent or co-catalyst presence in the reaction mixture. In metathesis of 1-octene, these catalysts showed considerably higher activity compared with MoO 3 supported on conventional silica with selectivity to 7-tetradecene being in the range between 60% and 95%. The highest activity exhibited MoO 3/MCM-41 with 6 wt.% of Mo (75% conversion after 6 h at 40 °C with selectivity to 7-tetradecene 84%). The turn-over-frequency of the catalysts loaded with 8 wt.% of Mo decreased in the order MCM-41 > MCM-48 > SBA-15, while the selectivity slightly increased in the same order. Using Raman spectroscopy, the differences in the catalytic activity were elucidated as a result of different dispersion of the active phase over the supports.

Vapour phase reaction of m-cresol and ethyl acetate over MCM-41 molecular sieves: One-pot synthesis of coumarin derivatives

Mesoporous Al-MCM-41 (Si/Al = 55 and 104) and Al,Zn-MCM-41 (Si/(Al + Zn) = 102) were synthesized by the surfactant-templated route. The catalytic activity was evaluated in the vapour phase reaction of m-cresol with ethyl acetate in the temperature range 200–400 °C. The identified products were 4,7-dimethylcoumarin (4,7-DMC), 2-acetyl-5-methylphenol (2A-5MP), 3-methylphenyl acetate (3-MPA), 2-ethyl-5-methylphenol (2E-5MP) and 4-ethyl-3-methylphenol (4E-3MP). Reaction parameters such as temperature, feed ratio and WHSV were optimised to obtain high 4,7-DMC selectivity at maximum conversion of m-cresol. The time-on-stream study revealed slow deactivation of the catalyst under optimum conditions. Though alkylation of m-cresol was the reaction, acylation dominated over alkylation, suggesting that ethyl acetate is also an active acylating agent for m-cresol. Ring acylation followed by esterification, and subsequent intramolecular condensation observed in this study, suggest an interesting novel one-pot route for the synthesis of coumarin derivatives in the vapour phase.

Speciation of CuO in MCM-41 during oxidation of naphthalene

By extended X-ray absorption fine structural (EXAFS) spectroscopy, copper oxide clusters with a square-plane structure are found in the channels of mesoporous molecular sieve MCM-41. Bond distances of Cu–O and Cu–Cu are 1.90 and 2.80 Å, respectively. Oxidation of naphthalene at 723 K for 4 h in MCM-41 leads to structural perturbation of the clusters (e.g., Cu–O: −0.02 Å and Cu–Cu: +0.02 Å) with little change in their coordination numbers.

Comparative studies of Zr-based MCM-41 and MCM-48 mesoporous molecular sieves: Synthesis and physicochemical properties

Two surfactant-templated synthetic routes are developed for the preparation of new types of mesoporous molecular sieves, Zr-MCM-41 and Zr-MCM-48, using different Si sources but keeping the same zirconium precursor (zirconium- n-propoxide). When fumed silica was used as Si precursor, a Zr-MCM-48 material of cubic structure was formed with a surface area of 654.8 m 2/g and an unimodal pore diameter distribution. It shows low stability: after calcination at 600 °C, the ordered structure was transformed into a relatively disordered worm-like mesostructure with many defects and silanol groups. The use of tetraethyl orthosilicate as Si source led to the formation of a Zr-MCM-41 mesoporous solid, which had good thermal stability and a highly ordered hexagonal arrangement, with a surface area 677.9 m 2/g and an uniform pore diameter distribution. Fourier transform infrared (FT-IR) characterization and 29Si NMR analysis confirm that zirconium ions indeed incorporated into the framework of the solid. The in situ FT-IR spectroscopy of pyridine adsorption reveals that both, Lewis and Brönsted acid sites, were formed on the surface of these mesoporous materials. The strength and number of the Brönsted acid sites of the Zr-MCM-48 solid were greater than those of the Zr-MCM-41, due to a lower degree of condensation reaction during the synthesis that led to more structural defects in the framework and more silanol groups stretching from the solid surface.

Asymmetric epoxidation of unfunctionalized olefins catalyzed by Mn(III) salen complex immobilized on MCM-48

Chiral Mn(III) salen complexes were supported on mesoporous molecular sieve MCM-48 and employed as catalyst in the asymmetric epoxidation of some unfunctionalized olefins. The as-synthesized catalysts showed excellent enantioselectivity than homogeneous catalysts for α-methylstyrene and the highest ee value (up to >99%) was obtained. Furthermore, these catalysts were also effective for bulkier olefins such as indene and 1-phenylcyclohexene. Compared to homogeneous counterparts, the heterogeneous catalysts are more stable and can be recycled three times without loss of enantioselectivity.

Conductivity of nanostructured mesoporous MCM-41 molecular sieve materials

MCM-41 molecular sieve materials have been investigated by means of impedance spectroscopy. Dielectric response of water confined in MCM-41 molecular sieve materials showed a power law dispersion, which was assigned to ac conductivity. This process, which occurs at temperatures close to room temperature, was found in all our investigated samples with the pore diameters ranging from 2.0 to 3.7 nm. Obtained values of the imaginary part of the complex dielectric permittivity were much larger than that of the bulk water. Such a phenomenon can be explained by the electrical response characteristic of the microstructural electrical network formed by water and hosting mesoporous silica material. The real part of conductivity has been calculated, and the influence of the pores size to electric conductivity and its mechanisms are discussed.

Global challenges and strategies for control, conversion and utilization of CO 2 for sustainable development involving energy, catalysis, adsorption and chemical processing

Utilization of carbon dioxide (CO 2) has become an important global issue due to the significant and continuous rise in atmospheric CO 2 concentrations, accelerated growth in the consumption of carbon-based energy worldwide, depletion of carbon-based energy resources, and low efficiency in current energy systems. The barriers for CO 2 utilization include: (1) costs of CO 2 capture, separation, purification, and transportation to user site; (2) energy requirements of CO 2 chemical conversion (plus source and cost of co-reactants); (3) market size limitations, little investment-incentives and lack of industrial commitments for enhancing CO 2-based chemicals; and (4) the lack of socio-economical driving forces. The strategic objectives may include: (1) use CO 2 for environmentally-benign physical and chemical processing that adds value to the process; (2) use CO 2 to produce industrially useful chemicals and materials that adds value to the products; (3) use CO 2 as a beneficial fluid for processing or as a medium for energy recovery and emission reduction; and (4) use CO 2 recycling involving renewable sources of energy to conserve carbon resources for sustainable development. The approaches for enhancing CO 2 utilization may include one or more of the following: (1) for applications that do not require pure CO 2, develop effective processes for using the CO 2-concentrated flue gas from industrial plants or CO 2-rich resources without CO 2 separation; (2) for applications that need pure CO 2, develop more efficient and less-energy intensive processes for separation of CO 2 selectively without the negative impacts of co-existing gases such as H 2O, O 2, and N 2; (3) replace a hazardous or less-effective substance in existing processes with CO 2 as an alternate medium or solvent or co-reactant or a combination of them; (4) make use of CO 2 based on the unique physical properties as supercritical fluid or as either solvent or anti-solvent; (5) use CO 2 based on the unique chemical properties for CO 2 to be incorporated with high ‘atom efficiency’ such as carboxylation and carbonate synthesis; (6) produce useful chemicals and materials using CO 2 as a reactant or feedstock; (7) use CO 2 for energy recovery while reducing its emissions to the atmosphere by sequestration; (8) recycle CO 2 as C-source for chemicals and fuels using renewable sources of energy; and (9) convert CO 2 under either bio-chemical or geologic-formation conditions into “new fossil” energies. Several cases are discussed in more detail. The first example is tri-reforming of methane versus the well-known CO 2 reforming over transition metal catalysts such as supported Ni catalysts. Using CO 2 along with H 2O and O 2 in flue gases of power plants without separation, tri-reforming is a synergetic combination of CO 2 reforming, steam reforming and partial oxidation and it can eliminate carbon deposition problem and produces syngas with desired H 2/CO ratios for industrial applications. The second example is a CO 2 “molecular basket” as CO 2-selective high-capacity adsorbent which was developed using mesoporous molecular sieve MCM-41 and polyethylenimine (PEI). The MCM41-PEI adsorbent has higher adsorption capacity than either PEI or MCM-41 alone and can be used as highly CO 2-selective adsorbent for gas mixtures without the pre-removal of moisture because it even enhances CO 2 adsorption capacity. The third example is synthesis of dimethyl carbonate using CO 2 and methanol, which demonstrates the environmental benefit of avoiding toxic phosgene and a processing advantage. The fourth example is the application of supercritical CO 2 for extraction and for chemical processing where CO 2 is either a solvent or a co-reactant, or both. The CO 2 utilization contributes to enhancing sustainability, since various chemicals, materials, and fuels can be synthesized using CO 2, which should be a sustainable way in the long term when renewable sources of energy are used as energy input.

Synthesis of commercial important diethyl phthalate over Al-, Fe- and Al,Zn-MCM-41 molecular sieves

The synthesis of diethyl phthalate (DEP) from phthalic anhydride (PAH) and ethanol (EtOH) has been carried out successfully on aluminum-, iron- and zinc- containing MCM-41 molecular sieves. These catalysts were prepared by the hydrothermal method. The catalysts have been characterized by the XRD, BET (surface area) and 29Si and, 27Al MAS-NMR techniques. The catalytic activity of these molecular sieves has been tested by the above-mentioned reaction, by the batch processes at 135, 150 and 175 °C. Both conversion and selectivity increased with an increase in temperature and mole ratio (EtOH/PAH). The activity of these catalysts followed the order: Al-MCM-41 (Si/Al = 112) > Fe-MCM-41 (Si/Fe = 115) > Al-MCM-41 (Si/Al = 70) > Al-MCM-41 (Si/Al = 52) > Fe-MCM-41 (Si/Fe = 61) > Al, Zn-MCM-41 (Si/Al + Zn = 104) > Al-MCM-41 (Si/Al = 30). The reaction yielded both monoethyl phthalate (MEP) and diethyl phthalate (DEP). The nature of the catalyst sites has been clarified using water as an impurity. The weight of the catalyst was optimized at 0.06 g. Some times hydrophilic and some times hydrophobic nature of the catalyst been explained by the influence of water; the external surface acidity also facilitates the reaction. This has been confirmed by the addition test reaction.

Synthesis, structure and magnetic properties of porous magnetic composite, based on MCM-41 molecular sieve with Fe 3O 4 nanoparticles

Porous magnetic composites were prepared by the synthesis of molecular sieve MCM-41 in the presence of Fe 3O 4 nanoparticles with average diameter of 15 nm. Nanoparticles were captured by porous silica matrix MCM-41, which resulted in their incorporation, as it was confirmed by TEM, SEM and X-ray diffraction. The materials possessed high surface area (392–666 m 2 g −1), high pore volume (0.39–0.73 cm 3 g −1) along with high magnetic response ( M S up to 28.4 emu g −1 at 300 K). Calcination of samples resulted in partial oxidation of Fe 3O 4 to α-Fe 2O 3. The influence of nanoparticles content on sorption and magnetic properties of the composites was shown. No hysteresis was found for the samples at 300 K; at 5 K, H C was in the range 370–385 G for non-calcinated samples and 350–356 G for calcinated ones.

Hydrogenation of Naphthalene on HY/MCM-41 Composite Supported Sulfided Ni-Mo Catalysts

A series of mesoporous molecular sieves, MCM-41 with different Si/Al molar ratios, were synthesized by hydrothermal method. The influence of aluminum content on the properties and pore structure of MCM-41 molecular sieves was investigated. The supported Ni-Mo catalysts with MCM-41 and γ-Al2O3 as supports were synthesized by impregnating with Ni-Mo-P solution. The activity of the catalysts was characterized by hydrogenation of naphthalene. The influence of Si/Al ratio of MCM-41 on hydrogenation activity of the catalysts was investigated. The results indicated that the relative crystallinity of MCM-41 decreases with the increase of aluminum content in the molecular sieves; however, the hydrogenation activity of the catalysts, especially the ring-opening activity, increases with the increase of aluminum content. The synergistic effect for hydrogenation of naphthalene was found by mixing MCM-41 and HY molecular sieves. At 360°C the catalysts with HY and MCM-41 mixture as supports had higher activity. The reaction network for hydrogenation of naphthalene includes two parallel pathways; naphthalene was hydrogenated to tetralin, then the isomerization and ring-opening of tetralin occurred, or tetralin was further hydrogenated to decalin, followed by the isomerization and ring-opening of decalin.

Collective excitations in liquidD2confined within the mesoscopic pores of a MCM-41 molecular sieve

We present a comparative study of the excitations in bulk and liquid ${\mathrm{D}}_{2}$ confined within the pores of MCM-41. The material (Mobile Crystalline Material-41) is a silicate obtained by means of a template that yields a partially crystalline structure composed by arrays of nonintersecting hexagonal channels of controlled width having walls made of amorphous ${\mathrm{SiO}}_{2}$. Its porosity was characterized by means of adsorption isotherms and found to be composed by a regular array of pores having a narrow distribution of sizes with a most probable value of $2.45\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The assessment of the precise location of the sample within the pores is carried out by means of pressure isotherms. The study was conducted at two pressures which correspond to pore fillings above the capillary condensation regime. Within the range of wave vectors where collective excitations can be followed up $(0.3\ensuremath{\leqslant}Q\ensuremath{\leqslant}3.0\phantom{\rule{0.3em}{0ex}}{\mathrm{\AA{}}}^{\ensuremath{-}1})$, we found confinement brings forward a large shortening of the excitation lifetimes that shifts the characteristic frequencies to higher energies. In addition, the coherent quasielastic scattering shows signatures of reduced diffusivity.