Showing papers on "MCM-41 published in 2010"

Recent Advances in Catalysis Over Mesoporous Molecular Sieves

Abstract: This overview covers the recent achievements in the application of mesoporous molecular sieves as catalysts and catalyst supports. Main structural and textural features are outlined in relation to the novel synthesis approaches of mesoporous molecular sieves and understanding of their properties. For application of mesoporous molecular sieves as catalysts different ways of introduction of active sites on their surfaces are provided. The main part describes selected catalytic reactions catalyzed by mesoporous molecular sieves focused on very recent papers. The examples include metathesis, acylation reactions, C–C coupling reactions of Heck and Suzuki types, base-catalyzed reactions (Knoevenagel and Michael additions, Claisen-Schmidt condensation, Tischenko reaction) and last but not least immobilization of organometallic complexes for different catalytic applications including chiral catalysts.

Conversion of Vegetable Oils into Hydrocarbons over CoMo/MCM-41 Catalysts

Abstract: Deoxygenation of triglycerides over Co and Mo sulfides supported on a series of mesoporous molecular sieves (MCM-41) with varying Si/Al ratio has been investigated in this contribution. The catalysts were tested in a flow reactor at reaction temperatures 300 and 320 °C, hydrogen pressures 2–11 MPa and space velocities 1–4 h−1 using refined rapeseed oil as a feedstock. Incorporation of Al into the framework of MCM-41 led to an increase of both conversion of triglycerides and selectivity to hydrocarbons, namely n-heptadecane and n-octadecane. However, the conversion of triglycerides was lower than that achieved over alumina supported CoMo. Moreover, the rather high selectivity to oxygenated products, as compared with alumina supports, has made possible a detailed description of the reaction intermediates and their dependence on the reaction conditions.

Synthesis of thiol-functionalized MCM-41 mesoporous silicas and its application in Cu(II), Pb(II), Ag(I), and Cr(III) removal

Abstract: Thiol-functionalized MCM-41 mesoporous silicas were synthesized via evaporation-induced self-assembly. The mesoporous silicas obtained were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy (FTIR), elemental analysis (EA), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The products were used as adsorbents to remove heavy metal ions from water. The mesoporous silicas (adsorbent A) with high pore diameter (centered at 5.27 nm) exhibited the largest adsorption capacity, with a BET surface area of 421.9 m2 g−1 and pore volume of 0.556 cm3 g−1. Different anions influenced the adsorption of Cu(II) in the order NO3− < OAc− < SO42− < CO32− < Cit− < Cl−. Analysis of adsorption isotherms showed that Cu2+, Pb2+, Ag+, and Cr3+ adsorption fit the Redlich–Peterson nonlinear model. The mesoporous silicas synthesized in the work can be used as adsorbents to remove heavy metal ions from water effectively. The removal rate was high, and the adsorbent could be regenerated by acid treatment without changing its properties.

ZnO nanoparticles supported on mesoporous MCM-41 and SBA-15: a comparative physicochemical and photocatalytic study

Abstract: A simple solvothermal impregnation method was used to prepare ZnO nanoparticles supported on MCM-41 and SBA-15. X-ray powder diffraction, N2 adsorption–desorption, Electron Probe Micro Analysis (EPMA), and UV–vis spectroscopy were used to characterize the prepared materials. The influence of the ZnO loading of different supports on the structural characteristics and the photocatalytic activity toward degradation of methylene blue in water under ultraviolet irradiation were investigated. Wide angle X-ray diffraction and UV–vis Diffuse Reflectance confirmed the existence of ZnO phase. A much smaller influence of impregnation with ethanolic zinc salt solution on the porosity was observed for SBA-15 compared with MCM-41. Finally, the adsorption and photocatalytic activity of the ZnO/mesoporous materials depend on porous characteristics of the support materials.

Synthesis of chloropropylamine grafted mesoporous MCM-41, MCM-48 and SBA-15 from rice husk ash: their application to CO2 chemisorption

Abstract: Mesoporous siliceous MCM-41, MCM-48 and SBA-15 were synthesized using Rice Husk Ash (RHA) as the silica source. Their defective –OH sites were then grafted with 3-chloropropyl amine hydrochloride (3-CPA) and characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and BET techniques. Those results portrayed their resemblance with that synthesized from conventional silica sources. 3-CPA grafted mesoporous silicas were tested for CO2 chemisorption over fixed bed reactor at different temperatures. The maximum adsorption of 1.7 mmol/g of CO2 was observed on 3-CPA grafted SBA-15 (SBA-15/CPA) at 25°C. The chemisorbed CO2 on amine grafted mesoporous silica was stabilized by weak hydrogen bonds formed during the nucleophilic attack between lone pair of electrons in amine groups and quadrupolar CO2 with more degree of positive charge to form carbamates. The rapid steep slope which arises due to CO2 adsorption illustrated a minimal mass transfer effect and extreme fast kinetics. Performance tests such as reproducibility, stability and selectivity towards CO2 adsorption were also carried out over 3-CPA grafted mesoporous silica and the results were in line with that of well established CO2 sorbent.

Synthesis of Some Novel 2-Aryl-Substituted2,3-Dihydroquinazolin-4(1H)-ones underSolvent-Free Conditions Using MCM-41-SO3H as a Highly EfficientSulfonic Acid

Abstract: MCM-41-SO3H, ordered mesoporous silica material MCM-41 with covalently anchored sulfonic acid groups located inside the mesochannels, was used as an acid catalyst for the rapid and ‘green’ synthesis of 2,3-dihydroquinazolin-4(1H)-one derivatives under solvent-free condition. This novel synthetic method offers several advantages, such as excellent yields, simple procedure, short reaction times, and mild reaction conditions.

Synthesis, characterization, and in vitro pH-controllable drug release from mesoporous silica spheres with switchable gates.

Abstract: To accomplish pH-controllable drug release on mesoporous carrier, one of the best ways is to graft stimuli-responsive organic molecules around mesopore outlets. In this work, the pH-responsive propyldiethylenetriamine groups (abbreviative phrase: multiamine chains) were grafted around mesopore outlets of mesoporous silica spheres (MSS) and expected to act as pH-responsive gates. To this end, three multiamine-grafted MSS (i.e., NM1, NM2, and NM3) were synthesized under different reaction temperatures and reaction times. The reaction temperature and time for multiamine grafting were 25 °C and 12 h for NM1, 100 °C and 1 h for NM2, and 100 °C and 12 h for NM3, respectively. Through systematic investigations of TEM, SEM, N2 adsorption/desorption, TG, and 29Si MAS NMR, it was found that NM3 had the highest grafting amount of multiamine chains. It was further confirmed that the multiamine chains around the pore outlets of NM3 played the role of “molecular switch” that could well control the transport of guest dr...

Zirconium doped MCM-41 supported WO3 solid acid catalysts for the esterification of oleic acid with methanol

Abstract: A series of zirconium doped MCM-41 silica supported WO x solid acid catalysts, with WO 3 loading ranging from 5 to 25 wt%, has been prepared by impregnation with ammonium metatungstate, and subsequent activation at temperatures between 450 and 800 °C. XRD, Raman and UV–vis spectroscopies have allowed us to establish that at temperatures higher than 700 °C occurs the formation of (WO) x /ZrO 2 nanoparticles on the surface of MCM-41 support, which exhibit acidic properties and are active in the esterification of oleic acid with methanol at 65 °C. WO 3 loadings of 15–20 wt%, after activation at 700 °C, lead to the most active catalysts, with conversion values close to 100%. The catalyst with 15 wt% WO 3 is stable even when the reaction is carried out at 200 °C, reusable at least during four cycles and no leaching of tungsten species in the liquid phase was found.

Al-MCM-41 as methanol dehydration catalyst

Abstract: Al-MCM-41, [SiO2]/[Al2O3] = 30, mesoporous catalysts were synthesized using tetraethylorthosilicate (TEOS) as a source of silica and hexadecyltrimethylammonium bromide (CTAB) as a structure-directing agent (SDA) in the presence of tetrapropylammonium hydroxide (TPAOH) as a co-surfactant additive. The catalytic activities of the calcined samples were evaluated for the dehydration of methanol to dimethyl ether (DME) at 250–450 °C and a gas hourly space velocity (GHSV) of 14,000–80,000 mL g−1cat h−1. Al-MCM-41 samples synthesized in the presence of TPAOH showed higher activity than those synthesized in its absence. The improvement in catalytic activity correlates with the increase in acidity brought about by the enhanced condensation of aluminosilicate framework in the Al-MCM-41 structure. Al-MCM-41 catalysts were also combined with methanol synthesis catalysts to form bifunctional catalysts for the synthesis DME from CO2/H2 at temperature, 260 °C; pressure, 735 psi; GHSV, 2000 mL g−1cat h−1 in a fixed-bed reactor.

A study on hydrogen-storage behaviors of nickel-loaded mesoporous MCM-41.

Abstract: The objective of the present work was to investigate the possibility of improving the hydrogen-storage capacity of mesoporous MCM-41 containing nickel (Ni) oxides (Ni/MCM-41). The MCM-41 and Ni/MCM-41 were prepared using a hydrothermal process as a function of Ni content (2, 5, and 10 wt.% in the MCM-41). The surface functional groups of the Ni/MCM-41 were identified by Fourier transform infrared spectroscopy (FTIR). The structure and morphology of the Ni/MCM-41 were characterized by X-ray diffraction (XRD) and field emission transmission electron microscopy (FE-TEM). XRD results showed a well-ordered hexagonal pore structure; FE-TEM also revealed, as a complementary technique, the structure and pore size. The textural properties of the Ni/MCM-41 were analyzed using N2 adsorption isotherms at 77 K. The hydrogen-storage capacity of the Ni/MCM-41 was evaluated at 298 K/100 bar. It was found that the presence of Ni on mesoporous MCM-41 created hydrogen-favorable sites that enhanced the hydrogen-storage capacity by a spillover effect. Furthermore, it was concluded that the hydrogen-storage capacity was greatly influenced by the amount of nickel oxide, resulting in a chemical reaction between Ni/MCM-41 and hydrogen molecules.

Direct synthesis of hydrogen peroxide from hydrogen and oxygen over palladium catalyst supported on SO3H-functionalized mesoporous silica

Abstract: Palladium catalysts supported on SO 3 H-functionalized mesoporous silicas (denoted as Pd/SO 3 H-MCM-41, Pd/SO 3 H-MCM-48, Pd/SO 3 H-MSU-1, Pd/SO 3 H-SBA-15, and Pd/SO 3 H-MCF) were applied to the direct synthesis of hydrogen peroxide from hydrogen and oxygen. For comparison, palladium catalysts supported on mesoporous silicas (denoted as Pd/MCM-41, Pd/MCM-48, Pd/MSU-1, Pd/SBA-15, and Pd/MCF) were also employed for the direct synthesis of hydrogen peroxide. Selectivity for hydrogen peroxide, yield for hydrogen peroxide, and final concentration of hydrogen peroxide over Pd/SO 3 H-functionalized mesoporous silica catalysts were much higher than those over Pd/mesoporous silica catalysts. Yield for hydrogen peroxide increased with increasing acid density of Pd/SO 3 H-functionalized mesoporous silica. Pd/SO 3 H-functionalized mesoporous silicas efficiently served as an alternate acid source and as an active metal catalyst in the direct synthesis of hydrogen peroxide from hydrogen and oxygen.

Post-synthesis alumination of MCM-41: Effect of the acidity on the HDS activity of supported Pd catalysts

Abstract: Siliceous MCM-41 with different amount of alumina, from 0.25 up to 4.0 wt%, were prepared by impregnation of the MCM-41 with aqueous solution of Al(NO) 3 ·9H 2 O. The modified mesoporous silicas were then used as supports for Pd catalysts prepared by wet-impregnation from PdCl 2 precursor. Supports and corresponding Pd catalysts were characterized by XRD, XPS and NH 3 -TPD. The catalytic behavior was tested in the hydrodesulfurization (HDS) reaction of thiophene. An increase of the hydrodesulfurization activity with increasing alumina amount up to 0.5 wt% was observed. On the basis of the acidity change of the support and the structural modification underwent by the deposited palladium, the improved catalytic behavior was associated to the increased acidity of the supports and also to its effect on the palladium dispersion. A bi-functional mechanism, implying that metallic palladium activates the hydrogen and the thiophene molecules are adsorbed on the acid sites of the support, could be operative. However, the increased acidity was also responsible for the larger catalyst deactivation which limited the beneficial effect up to a certain amount of alumina content.

A facile method for promoting activities of vanadium–schiffbase complex anchored on organically modified MCM-41 in epoxidation reaction

Abstract: An organic–inorganic hybrid heterogeneous catalyst (V-MCM-41) was synthesized by anchoring vanadium–schiffbase complex on chloropropyl modified mesoporous silica (CP-MCM-41). Characterization of the functionalized ordered two-dimensional mesoporous material by powder X-ray diffraction (XRD), N2 adsorption–desorption, CP-MAS NMR spectroscopy (13C and 29Si), Fourier transform infrared spectroscopy (FT-IR), diffuse-reflectance UV–vis spectroscopy, demonstrate the successful grafting of vanadium complex into the functionalized mesoporous silica. It is also observed that the mesostructure has not been destroyed in multistep synthetic procedure. We have performed the epoxidation reaction of various olefins using V-MCM-41 as the catalyst, hydrogen peroxide as the oxidant and sodium bicarbonate as the co-catalyst in acetonitrile solvent. The co-catalyst enhances the rate of reaction by many folds. The reaction requires minimum amount of H2O2, short time period and most importantly occurs at room temperature. The heterogeneous catalyst can be recovered easily and reused many times without significant loss in catalytic activity and selectivity.

Effects of zirconia promotion on the structure and performance of smaller and larger pore silica-supported cobalt catalysts for Fischer–Tropsch synthesis

Abstract: The effects of modification with zirconia on the properties of cobalt species in cobalt Fischer–Tropsch catalysts supported by mesoporous silicas with different porous structures were investigated using nitrogen adsorption, X-ray diffraction, temperature programmed reduction, in situ magnetic measurements and X-ray absorption. The catalysts were prepared by sequential incipient impregnation using solutions of cobalt nitrate and zirconyl nitrate. The effects of zirconia modification on the structure and performance of cobalt based catalysts differ considerably with cobalt catalysts supported by smaller pore MCM-41 and larger pore SBA-15 silicas. In SBA-15 supported samples, modification with zirconia did not result in any significant change in cobalt reducibility and dispersion. Therefore, the concentration of active cobalt metal surface sites on all SBA-15 supported catalysts was comparable, which led to the similar catalytic performance in Fischer–Tropsch synthesis. In MCM-41 supported cobalt catalysts zirconia promotion weakened the cobalt–silica interaction and led to the preferential localization of Co 3 O 4 crystallites on the outer surface of the support. Higher zirconia loading led to larger cobalt particles in the zirconia-modified CoMCM-41 catalysts which displayed easier cobalt reduction. The catalytic activity of CoMCM-41 catalysts in Fischer–Tropsch reaction passed through a maximum as a function of zirconia content. The highest activity corresponded to the maximum concentration of cobalt metal sites.