Showing papers on "MCM-41 published in 2017"

Dibenzothiophene hydrodesulfurization with NiMo and CoMo catalysts supported on niobium-modified MCM-41

Abstract: In the present work, we studied the effect of the addition of niobium to CoMo/MCM-41 and NiMo/MCM-41 catalysts on their characteristics and performance in the hydrodesulfurization of dibenzothiophene. The MCM-41 support was synthesized at room temperature according to a well-known procedure. The metal species (Nb, Mo, Ni or Co) were deposited by successive impregnation using aqueous solutions of the corresponding metal salts. MCM-41 and Nb-containing MCM-41 supports were characterized by X-ray diffraction, N 2 physisorption, FT-Raman spectroscopy, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectroscopy and scanning electron microscopy. The CoMo and NiMo catalysts in oxide state, in addition to the above techniques, were characterized by temperature-programmed reduction and the sulfided catalysts were characterized by high resolution transmission electron microscopy. The results show that the incorporation of small amounts of Nb (3–5 wt.%) increased the catalytic activity of both NiMo and CoMo catalysts in dibenzothiophene hydrodesulfurization and affected their selectivity. The effect of Nb on the selectivities of the NiMo and CoMo catalysts was different: for the NiMo catalysts, Nb increased selectivity towards the HYD route, whereas for the CoMo catalysts, it increased selectivity towards the DDS route. The analysis of the effect of Nb on the catalysts’ selectivity was performed based on the kinetic constants calculated for the different steps of the DBT HDS network.

Hydrothermal Synthesis of Mesoporous Silica MCM-41 Using Commercial Sodium Silicate

Abstract: In this work, ordered mesoporous silica MCM-41 was pre- pared by hydrothermal synthesis using industrial-grade sodium silicate (Na2SiO3) as silica source, hexadecyltrimethyl-ammonium bromide (CTAB) as template agent and ethyl acetate as pH regulator. The in- fluence of CTAB/SiO2 molar ratio, reaction time, aging temperature, and co-surfactant type on the structural and morphological properties of the obtained silica was studied. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption-de- sorption isotherms. Ordered mesoporous MCM-41 silica was obtained at 80 °C by using a range of CTAB/SiO2 molar ratio from 0.35 to 0.71 and reaction times up to 72 h and isopropanol (i-PrOH) as co- surfactant.

Selective oxidation of benzyl alcohol through eco-friendly processes using mesoporous V-MCM-41, Fe-MCM-41 and Co-MCM-41 materials

Abstract: MCM-41 nanostructured materials modified with Vanadium, Iron and Cobalt were synthesized by a hydrothermal method. The catalysts were characterized by XRD, UV–Vis-DR, ICP-OES and N 2 adsorption. All the catalysts showed good structural order and high specific areas; however the lowest value in these parameters, corresponding to the Co-M(60) sample, could be due to the higher presence of oxide species determined by UV–Vis-DR. These mesoporous metalosilicates were evaluated in the liquid phase oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) using H 2 O 2 as oxidant. Results showed that V-M(60) had better catalytic performance than Fe-M(60) and Co-M(60) exhibiting high TON (1100 mol/mol V), selectivity to BzH (95%) and 31.7% yield at 7 h under optimized reaction conditions. The main reason for the enhanced catalytic performance was attributed to the well dispersion of vanadium species in the framework which could be considered as the active sites for the benzyl alcohol oxidation reaction. At the same time, the catalyst could be recovered and effectively reused during three cycles without a significant loss in its activity and selectivity.

Alcohols react with MCM-41 at room temperature and chemically modify mesoporous silica.

Abstract: Mesoporous silica has received much attention due to its well-defined structural order, high surface area, and tunable pore diameter. To successfully employ mesoporous silica for nanotechnology applications it is important to consider how it is influenced by solvent molecules due to the fact that most preparation procedures involve treatment in various solvents. In the present work we contribute to this important topic with new results on how MCM-41 is affected by a simple treatment in alcohol at room temperature. The effects of alcohol treatment are characterized by TGA, FTIR, and sorption calorimetry. The results are clear and show that treatment of MCM-41 in methanol, ethanol, propanol, butanol, pentanol, or octanol at room temperature introduces alkoxy groups that are covalently bound to the silica surface. It is shown that alcohol treated MCM-41 becomes more hydrophobic and that this effect is sequentially more prominent going from methanol to octanol. Chemical formation of alkoxy groups onto MCM-41 occurs both for calcined and hydroxylated MCM-41 and the alkoxy groups are hydrolytically unstable and can be replaced by silanol groups after exposure to water. The results are highly relevant for mesoporous silica applications that involve contact or treatment in protic solvents, which is very common.

Anchoring of Cu(II)–vanillin Schiff base complex on MCM‐41: A highly efficient and recyclable catalyst for synthesis of sulfides and 5‐substituted 1H–tetrazoles and oxidation of sulfides to sulfoxides

Abstract: A copper(II)–vanillin complex was immobilized onto MCM-41 nanostructure and was used as an inexpensive, non-toxic and heterogeneous catalyst in the synthesis of symmetric aryl sulfides by the cross-coupling of aromatic halides with S8 as an effective sulfur source, in the oxidation of sulfides to sulfoxides using 30% H2O2 as a green oxidant and in the synthesis of 5-substituted 1H–tetrazoles from a smooth (3 + 2) cycloaddition of organic nitriles with sodium azide (NaN3). The products were obtained in good to excellent yields. This catalyst could be reused several times without loss of activity. Characterization of the catalyst was performed using Fourier transform infrared, energy-dispersive X-ray and atomic absorption spectroscopies, X-ray diffraction, thermogravimetric analysis, and scanning and transmission electron microscopies.

Influence of Aluminum Addition in the Framework of MCM-41 Mesoporous Molecular Sieve Synthesized by Non-Hydrothermal Method in an Alkali-Free System

Abstract: Purely siliceous MCM-41 and Al-containing MCM-41 (Al-MCM-41) mesoporous materials were synthesized by non-hydrothermal method in alkali-free ions medium at room temperature and short reaction times. Under these synthesis conditions, it was also investigated the influence of Al incorporation in the crystal structure of MCM-41. The solids were characterized by ICP-OES, AAS, N2 adsorption at 77 K, XRD, TEM, NH3-TPD, 27Al and 29Si-MAS-NMR, FT-IR and TGA. The resulting mesoporous materials showed a well-defined hexagonally ordered pore geometry maintaining a uniform and unimodal pore size distribution with high specific surface areas (1000-1400 m2g-1). The Al+3 ions were introduced successfully in the structure of the purely siliceous MCM-41 expanding the unit cell parameter and forming four-coordinated Al species, and in a less extent, forming six-coordinated Al species. In addition, the surface acidity of the MCM-41 increased with Al loading. Contrary, the presence of Al in the MCM-41 mesoporous structure resulted in a decrease of the crystallinity and specific surface area possibly due to the presence of Al species in highly distorted tetrahedral structures and Al extra-framework or amorphous alumina occluded in the pores. The MCM-41 type mesoporous materials obtained in this work show similar characteristics of those synthesized by conventional hydrothermal methods.

Surface Properties of Al-Functionalized Mesoporous MCM-41 and the Melting Behavior of Water in Al-MCM-41 Nanopores.

Abstract: We report an experimental investigation of structural and adhesive properties for Al-containing mesoporous MCM-41 and MCM-41 surfaces. In this work, highly ordered hexagonal mesoporous structures of aluminosilica with two different Si/Al molar ratios equal to 50 and 80 and silica samples were studied; Al was incorporated into the MCM-41 structures using the direct synthesis method, with CTAB as a surfactant. The incorporation of aluminum was evidenced simultaneously without any change in the hexagonal arrangement of cylindrical mesopores. The porous materials were examined by techniques such as low-temperature nitrogen sorption, energy-dispersive spectroscopy, and scanning and transmission electron microscopy. Surface properties were determined through X-ray photoelectron spectroscopy, potentiometric titration, and static contact angle measurements. It was shown that an increase in surface acidity leads to an increase in the wetting energy of the surface. To investigate the influence of acidity on the con...

Adsorption equilibria of rhodium acetylacetonate with MCM-41, MSU-H, and HMS silica substrates in supercritical carbon dioxide for preparing catalytic mesoporous materials

Abstract: Adsorption isotherms of rhodium(III) acetylacetonate (Rh(acac)3) in supercritical carbon dioxide (scCO2) with methanol co-solvent for three types of mesoporous silica (MCM-41, MSU-H, and HMS) at 313–353 K and at 15.0 MPa were measured using a fixed bed method. The measured adsorption equilibria varied among the adsorbent substrates and depended on the specific surface area and pore structure of the adsorbents. The amount of adsorbed Rh(acac)3 increased with increasing temperature owing to strong effects of the CO2 density. Fitting parameters determined from correlation of the data with the Dubinin-Astakhov (DA) equation demonstrated that the interaction of the precursor for the adsorbents, CO2 density and pore structure of adsorbents were dominant factors in the adsorption equilibria of metal precursors in scCO2. The impregnation of Rh on the silica supports by a batch method in scCO2 could be characterized by the DA equation for which Eprec showed correlation with impregnated Rh particle size and W0,prec showed correlation with Rh loading amount. The DA equation is useful for characterizing adsorption equilibria in mesoporous materials with scCO2 systems and allows estimation of conditions required for impregnating metals into mesoporous silica substrates.

Pd‐SBT@MCM‐41: As an efficient, stable and recyclable organometallic catalyst for C‐C coupling reactions and synthesis of 5‐substituted tetrazoles

Abstract: A palladium S-benzylisothiourea complex was anchored on functionalized MCM-41 (Pd-SBT@MCM-41) and applied as efficient and reusable catalyst for the synthesis of 5-substituted 1H–tetrazoles using [2 + 3] cycloaddition reaction of various organic nitriles with sodium azide (NaN3) in poly(ethylene glycol) (PEG) as green solvent. Also this catalyst was applied as an versatile organometallic catalyst for Suzuki cross-coupling reaction of aryl halides and phenylboronic acid (PhB(OH)2) or sodium tetraphenyl borate (NaB(Ph)4). This nanocatalyst was characterized by thermal gravimetric analysis (TGA), X-ray Diffraction (XRD), scanning electron microscopy (SEM), inductively Coupled Plasma (ICP) and N2 adsorption–desorption isotherms techniques. Recovery of the catalyst is easily achieved by centrifugation for several consecutive runs.

Creating an Optimal Microenvironment within Mesoporous Silica MCM-41 for Capture of Tobacco-Specific Nitrosamines in Solution.

Abstract: To meet the requirement of capturing tobacco-specific nitrosamines (TSNA) for environment protection, a unique microenvironment was carefully created inside the channels of mesoporous silica MCM-41. In situ carbonization of template micelles at 923 K, combined with the excess aluminum used in one-pot synthesis of MCM-41, is adopted to tailor the tortuosity of mecsoporous channels, while loaded metal oxides (5 wt %) and the Al component in the framework are employed to exert the necessary electrostatic interaction toward the target carcinogens TSNA in solution. The elaborated microenvironment created in mesoporous sorbents was characterized with XRD, N2 adsorption–desorption, TEM, XPS, and TG-DSC methods. Various solutions of Burley- and Virginia-type tobaccos were used to assess the adsorption performance of new mesoporous sorbents, and the influence of the solid-to-liquid ratio, adsorption time, and loading amount of CuO on the adsorption was carefully examined. The representative sample 5%Cu/AM-10c coul...

Fabrication of Amine and Zirconia on MCM‐41 as Acid–Base Catalysts for the Fixation of Carbon Dioxide

Abstract: Highly porous catalysts based on MCM-41 with both acidic and basic sites such as ZrO2 as an acid and amino propane triethoxy silane (APTES) as mild base are fabricated and characterized thoroughly XRD, SEM, TGA, TPRDO, BET, EDS, XPS and IR analysis. This catalyst shows synergistic effect for the activation of epoxide as well as carbon dioxide to synthesize cyclic carbonates. The presence of the free amine functional group activates the carbon dioxide molecule by absorption while the presence of zirconium metal activates the epoxide ring. The effect of amine loading and catalyst loading on cycloaddition reaction studied. Additionally, the cycloaddition reactions proceeds under solvent free, at mild reactions condition and the catalysts are recyclable in nature.

Titanium alkylphosphate functionalised mesoporous silica for enhanced uptake of rare-earth ions

Abstract: The separation of rare-earth elements (REEs) is usually carried out by a multi-stage solvent extraction process utilising organophosphorus extractants. Inspired by the structure of the solvating extractant tri-n-butyl phosphate (TBP), new sorbents were designed by covalently attaching short n-alkyl chains (ethyl, n-propyl and n-butyl) to titanium(IV) phosphate functionalised mesoporous MCM-41 silica by a layer-by-layer grafting route. Mesoporous MCM-41 silica served as a versatile porous support and the grafted titanium(IV) derivatives provided enhanced acid stability and solvating extraction capability. Various characterisation methods including solid-state 13C, 29Si and 31P magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and simultaneous thermogravimetry and differential scanning calorimetry-mass spectroscopy (TG/DSC-MS) were used to confirm the ligand attachment. The hybrid materials showed a better uptake of rare-earth ions from nitrate feed solution than the unmodified inorganic material. The optimal separation factor (SF) obtained for scandium–lanthanum separation is in excess of 100 000 at pH 2.1. The SFs calculated for dysprosium–neodymium are approximately 3, which is comparable to that of TBP in a typical solvent extraction setup. This study provides a new strategy to design inorganic–organic hybrid sorbents based on the structure of organophosphorus extractants via metal(IV)–O–P bonds.

Synthesis of 2,3-dihydroquinazolin-4(1H)-ones, disulfides and sulfoxides catalyzed by a zinc complex immobilized onto functionalized mesoporous MCM-41 as a mild and efficient catalyst

Abstract: Zinc complex with 2-amino-3-hydroxy-pyridine ligand was immobilized onto chloropropyl-modified mesoporous silica MCM-41 (CP-MCM-41) via post-grafting method. The prepared catalyst has been characterized by low-angle X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive spectrum, atomic adsorption spectroscopy and thermogravimetric analysis. The immobilized nano-structured material showed very good catalytic activity and excellent recycling efficiencies for the oxidation reaction of sulfides to sulfoxides and oxidative coupling of thiols to their corresponding disulfides in the presence of aqueous hydrogen peroxide as oxidant at room temperature and the synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives in water.