Showing papers on "MCM-41 published in 2013"

A facile and efficient synthesis of styrene carbonate via cycloaddition of CO2 to styrene oxide over ordered mesoporous MCM-41-Imi/Br catalyst

Abstract: MCM-41 was successfully immobilized with imidazole using 3-chloropropyltriethoxysilane (CPTES) as the anchoring agent followed by alkylation with 1,2-dibromoethane at 110 °C. The resulting catalyst was designated as MCM-41-Imi/Br. TEM showed the catalyst had ordered mesoporous straight-channels with average wall thickness of 2.14 nm and average pore size of 1.56 nm. The 29Si MAS NMR analysis confirmed the presence of T2, T3, Q3 and Q4 silicon centers. The 13C MAS NMR showed that MCM-41-Imi/Br had three chemical shifts corresponding to the three carbon atoms of the propyl group. The aromatic imidazole peaks were detected at 110–140 ppm. The catalyst was used in the solvent-less synthesis of styrene carbonate (SC) from CO2 and styrene oxide (SO) under ambient conditions. It was demonstrated that the synergistic effect due to the stronger nucleophilicity of Br− and amine in the catalyst could lead to a maximum selectivity of 99.1%. Based on the results, a plausible reaction mechanism was proposed for the catalytic reaction. The catalyst could be recovered and reused several times without significant loss in the catalytic activity.

Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 for methanol dehydration to dimethyl ether: Effect of SiO2/Al2O3 ratio in H-ZSM-5

Abstract: Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5 zeolite as source and characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, N 2 adsorption and desorption measurement, and NH 3 temperature-programmed desorption. The effect of SiO 2 /Al 2 O 3 ratio in H-ZSM-5 on the structure, surface acidity and catalytic performances of H-ZSM-5/MCM-41 for methanol dehydration to dimethyl ether were investigated. H-ZSM-5/MCM-41 prepared with H-ZSM-5 of different SiO 2 /Al 2 O 3 ratios as source in which H-ZSM-5 nanoparticles were uniformly dispersed in MCM-41 matrix, had well-ordered micropores and mesopores. The acid amount and strength of moderate acid sites ( T P1 ) of H-ZSM-5/MCM-41 can be controlled by the SiO 2 /Al 2 O 3 ratio in H-ZSM-5 during the range from 25 to 50. Among these catalysts, H-ZSM-5/MCM-41 presented a comparable catalytic activity to the corresponding pure H-ZSM-5 and 100% dimethyl ether selectivity in a wider temperature range than the corresponding pure H-ZSM-5. The excellent catalytic performances were due to the highly active and uniform strong acid sites and the hierarchical porosity in the micro-mesoporous composite molecular sieves. The catalytic mechanism of H-ZSM-5/MCM-41 for the methanol dehydration to dimethyl ether was also discussed.

Metathesis of 2-butene to propylene over W-mesoporous molecular sieves: A comparative study between tungsten containing MCM-41 and SBA-15

Abstract: Mesoporous silica (MCM-41 and SBA-15) having tungsten oxide in the framework was synthesized by hydrothermal crystallization process using CTAB and P123 as structure directing agents, respectively. Tungsten oxide was supported on the MCM-41 and SBA-15 by wet impregnation method for a comparative study. The synthesized materials were characterized by XRD, N2 adsorption–desorption, NH3-TPD, pyridine-FT-IR, UV–vis DRS and Raman spectroscopy techniques. The catalysts were used to perform metathesis reaction of 2-butene in a fixed-bed reactor at different temperatures and under atmospheric pressure. It was observed that catalysts having tungsten oxide in the framework of mesoporous silica exhibited higher activity as compared to tungsten oxide impregnated catalysts. The results revealed that WO3-MCM-41(30) catalyst has much higher activity at a low temperature (450 °C) as compared to WO3-SBA-15(30). At 550 °C, WO3-MCM-41(30) and WO3-SBA-15(30) showed comparable activity with highest propylene yield of 39 mol% and 37 mol%, respectively. The higher metathesis activity of WO3-MCM-41 catalysts can be related to the well-dispersed active tetrahedral tungsten oxide species as evidenced from XRD, UV–vis DRS and Raman spectroscopy results.

Hydrogenation of dimethyl oxalate to ethylene glycol over mesoporous Cu‐MCM‐41 catalysts

Abstract: The synthesis and utilization of mesoporous Cu-MCM-41 catalysts for hydrogenation of dimethyl oxalate to ethylene glycol is described in this article. Physicochemical properties of these Cu-MCM-41 catalysts have been investigated by N2-physisorption, X-ray diffraction, inductively coupled plasma, N2O titration, transmission electron microscopy, temperature programmed reduction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. It was found that the copper loading significantly influenced the pore structure and copper surface area of the catalyst. High catalytic performance is obtained over a 20Cu-MCM-41 catalyst with a full DMO conversion and EG yield of 92% at a LHSV of 3.0 h−1. The catalytic performance of optimized 20Cu-MCM-41 catalyst could be attributed to the fine copper dispersion and large copper surface areas. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2530–2539, 2013

Effect of Ni Particle Location within the Mesoporous MCM-41 Support for Hydrogen Production from the Catalytic Gasification of Biomass

Abstract: Thermal processing of biomass in the presence of a catalyst is a promising technology to generate H-rich gases for fuelling the future. Metal particles loaded on porous supports have been widely used for biomass gasification. However, no detailed research has been designed for describing the catalytic performance of nickel particles located inside compared to outside the pores of the supports. In this work, two groups of Ni/MCM-41 catalysts were prepared: I-series catalysts where most of the NiO particles were located inside the mesopores of MCM-41 and O-series catalysts where most of the NiO particles were located outside the pores of MCM-41. The prepared catalysts were used in the pyrolysis-catalytic gasification of wood sawdust using a two-stage fixed-bed reaction system. Gasification on the I-series catalysts generated more gas and hydrogen and lower oil, compared with the O-series catalysts. Hydrogen production was increased from 16.46 to 21.26 (mmol H g wood) when the catalyst was changed from 20%Ni-O to 20%Ni-I. The better performance of the I-series catalysts in relation to hydrogen production is suggested to be due to the longer residence time of pyrolysis reactants inside the pores of the MCM-41 and thus a longer contact time between reactants and active Ni sites. In addition, the high dispersion of the fine NiO particles inside the pores of the MCM-41 support enhances the catalytic performance of the I-series catalyst during the pyrolysis/gasification of biomass.

One-pot synthesis of Aluminum-containing ordered mesoporous silica MCM-41 using coal fly ash for phosphate adsorption

Abstract: The present study offers an economic one-pot synthesis of Al-containing ordered mesoporous silica MCM-41 from the coal fly ash. The samples were characterized by small-angle XRD, N2 adsorption, TEM, mapping, 27Al MAS NMR, EDX, and NH3-TPD. The effects of pH values to the final mesostructures have also been investigated. The results show that the material prepared at the pH value of 10 displays the largest pore volume of 0.98 cm3/g, the highest BET surface area of 1020 m2/g, and the lowest Si/Al molar ratio of 2. Using this material as adsorbent for phosphates, the adsorption capacity reaches 64.2 mg/g at 298 K, which is much higher than that of large pore mesoporous silica SBA-15 (53.5 mg/g), diatomite (62.7 mg/g), and MCM-41 (31.1 mg/g). In addition, the thermodynamics and kinetics for the phosphate adsorption were also investigated. Our present study shows an economic way to treat phosphates using the industrial solid waste of coal fly ash.

Amino acid-based ionic liquid immobilized on α-Fe2O3-MCM-41: An efficient magnetic nanocatalyst and recyclable reaction media for the synthesis of quinazolin-4(3H)-one derivatives

Abstract: For the first time, we report the synthesis and the application of magnetic nanocatalyst (α-Fe 2 O 3 )-MCM-41- l -prolinium nitrate which was characterized by XRD, TEM, IR, X-ray energy diffraction (XED) spectra and nitrogen physisorption measurements. l -prolinium nitrate (fully green amino acid-based ionic liquid) inside the mesochannels of (α-Fe 2 O 3 )-MCM-41 lead to prepare a new solid catalyst which was used as an efficient heterogeneous catalyst for the one-pot oxidative cyclization straight synthesis of quinazolin-4(3H)-one derivatives from isatoic anhydride, aldehyde or alkyl halide and primary amines under mild reaction conditions without using any oxidant with good to excellent yields. Moreover, it was proven that in these reactions, the use of such a hybrid material as a catalyst plays the role of rendering the reactions while neither the (α-Fe 2 O 3 )-MCM-41 nor the l -prolinium nitrate were not able to promote this reaction in the desired pathway toward the above mentioned product. The characteristic features of this catalyst are attributed to both acidic and oxidative behavior of the catalyst.

Synthesis and Catalytic Performance of ZSM-5/MCM-41 Zeolites With Varying Mesopore Size by Surfactant-Directed Recrystallization

Abstract: ZSM-5/MCM-41 zeolite composites with varying mesopore sizes were prepared through alkali-desilication and surfactant-directed recrystallization with different chain length of alkyltrimethylammonium bromide. XRD and TEM revealed that the composites possessed the characteristics of both ZSM-5 and mesoporous MCM-41 with hexagonal symmetry. N2-adsorption–desorption, 27Al MAS NMR, NH3-TPD and in situ FT-IR results suggested that the sizes of the mesopores and the accessibility of acid sites could be affected greatly by the chain length of alkyltrimethylammonium bromide used. Catalytic cracking of n-dodecane over ZSM-5/MCM-41 composites was studied in the form of coatings on the inside of a tubular reactor at 550 °C and 4 MPa. The conversion of n-dodecane increased gradually with increasing the mesopore sizes of ZSM-5/MCM-41 composites, implying a positive effect of the mesopores on the diffusion inside pore channels and the accessibility of acid sites by the reactants.

Quick photo-Fenton degradation of phenolic compounds by Cu/Al2O3-MCM-41 under visible light irradiation: small particle size, stabilization of copper, easy reducibility of Cu and visible light active material.

Abstract: The present study reports the photo-Fenton degradation of phenolic compounds (phenol, 2-chloro-4-nitrophenol and 4-chloro-2-nitrophenol) in aqueous solution using mesoporous Cu/Al(2)O(3)-MCM-41 nanocomposite as a heterogeneous photo-Fenton-like catalyst. The in situ incorporation of mesoporous Al(2)O(3) (MA) into the framework of MCM-41 (sol-gel method) forms Al(2)O(3)-MCM-41 and wetness impregnation of Cu(II) on Al(2)O(3)-MCM-41 generates mesoporous Cu/Al(2)O(3)-MCM-41 composite. The effects of pH and H(2)O(2) concentration on degradation of phenol, 2-chloro-4-nitrophenol and 4-chloro-2-nitrophenol are studied. Kinetics analysis shows that the photocatalytic degradation reaction follows a first-order rate equation. Mesoporous 5 Cu/Al(2)O(3)-MCM-41 is found to be an efficient photo-Fenton-like catalyst for the degradation of phenolic compounds. It shows nearly 100% degradation in 45 min at pH 4. The combined effect of small particle size, stabilization of Cu(2+) on the support Al(2)O(3)-MCM-41, ease reducibility of Cu(2+) and visible light activeness are the key factors for quick degradation of phenolic compounds by Cu/Al(2)O(3)-MCM-41.

Sulfonic acid functionalized MCM-41 as solid acid catalyst for tert-butylation of hydroquinone enhanced by microwave heating

Abstract: a b s t r a c t Covalently linked sulfonic acid ( SO3H) modified MCM-41 mesoporous catalysts was prepared, char- acterized and its catalytic activity under microwave irradiation was evaluated. The NH2-MCM-41 was first prepared by anchoring (3-aminopropyl)triethoxysilane (APTES) on Si-MCM-41 and further reacted with 1,4-butane-sultone to yield the desired acid catalyst. The mesophase and porosity of samples were determined by XRD, TEM and N2 sorption isotherm analyses. The presence of sulfonic acid moiety was confirmed by FT-IR, TG/DTA, sulfur elemental analysis and in situ IR study of pyridine and ammonia adsorptions. The catalyst showed high catalytic activity and high selectivity in tert-butylation of hydro- quinone under microwave irradiation. No leaching problem was observed after several runs, while the catalyst can be recovered and reused without loss of reactivity under the described reaction conditions. © 2012 Elsevier B.V. All rights reserved.

Organic/inorganic MCM-41 magnetite nanocomposite as a solid acid catalyst for synthesis of benzo[α]xanthenone derivatives

Abstract: In the present study, for the first time the synthesis of organic–inorganic MCM-41 mesoporous magnetite nanoparticles (MNPs@MCM-41) as a new class of solid acid catalyst with large density of sulfonic acid groups was suggested. The specific surface area and textural property of synthesized nanoparticles were improved through the coupling of inorganic and organic components by template synthesis on the magnetite nanoparticle surface. The new solid acid catalyst was prepared in three steps: (i) preparation of colloidal iron oxide magnetite nanoparticles (Fe3O4 MNPs) with particle size lower than 8.0 nm, (ii) development of an organic–inorganic MCM-41 mesoporous structure with thiol groups on the surface of MNPs (Fe3O4@MCM-41 SH) and (iii) oxidation of thiol groups to sulfonic acid (Fe3O4@MCM-41 SO3H). The incorporation of sulfonic acid as a functional group on the surface of MNPs@MCM-41 was achieved by simultaneous reaction of condensable inorganic silica species and thionilayted organic compounds (co-condensation, one-pot synthesis) that lead to magnetite mesoporous solid acid catalyst. The properties of prepared magnetite nanocomposite were characterized by FT-IR, XRD, UV-DRS, TEM, VSM and titration. Finally, the applicability of the synthesized nanocomposites was tested as heterogeneous solid acid catalyst for one-pot three component synthesis of aryl benzo[α]xanthenone derivatives in room temperature and solvent free conditions.

Study on the effect of metal types in (Me)-Al-MCM-41 on the mesoporous structure and catalytic behavior during the vapor-catalyzed co-pyrolysis of pubescens and LDPE

Abstract: The catalysts (Me)-Al-MCM-41 (Me = Ni, Pd and their combination) were synthesized hydrothermally, characterized with XRD, BET, NH 3 -TPD, SEM, TEM, XPS, H 2 -TPR, chemisorption of hydrogen, and tested by experiments of co-pyrolysis of pubescens and LDPE under vapor-catalyzed condition. Characterization results suggested that the synthesis of Al-MCM-41 was successful, but the introduction of Me into Al-MCM-41 caused some changes in structure of catalyst to a certain degree, resulting in significant changes in their properties and catalytic behavior. The results obtained from vapor-catalyzed co-pyrolysis over these catalysts showed that there were some interactions between the intermediate species from the co-pyrolysis, as the relative content of aromatics in oil was high, whereas that of phenol in corresponding aqua was low, and vice versa. The type of metal in catalysts was of more importance than the metal siting. Moreover, all catalysts except Ni-Pd-Al-MCM-41 exerted strong effect of alkanisation on the primary intermediate species from the pyrolysis of LDPE, which demonstrated that the pore architecture of parent Al-MCM-41 and (Me)-Al-MCM-41 containing single Me strongly favored the reactions in relation to alkanisation; on the contrary, Ni-Pd-Al-MCM-41 exerted a strong effect of dehydrogenation on those primary intermediate species. More importantly, the synergistic effect on producing hydrogen, based on the 61.8 vol.% of H 2 in gaseous mixture, indicated that the combination of Ni and Pd in (Me)-Al-MCM-41 might bring about a novel performance during the vapor-catalyzed co-pyrolysis of biomass and plastics. It was predicted that Ni-Pd-Al-MCM-41 might play its special application in development of hydrogen energy, exploitation and utilization of biomass as well as municipal solid waste (MSW) such as waste plastics, etc. The major schemes of reactions involved in the vapor-catalyzed co-pyrolysis had been proposed.

A novel synthesis of Ni2P/MCM-41 catalysts by reducing a precursor of ammonium hypophosphite and nickel chloride at low temperature

Abstract: A novel method to prepare Ni 2 P/MCM-41 catalysts at low reduction temperature based on ammonium hypophosphite and nickel chloride by temperature programmed reduction is described. The catalysts were prepared using incipient wetness impregnation of the siliceous MCM-41 support with aqueous solutions of ammonium hypophosphite and nickel chloride, followed by reducing the obtained precursor at 483–663 K for 2 h in flowing H 2 , to form Ni 2 P catalysts. The catalysts were characterized by H 2 temperature-programmed reduction (H 2 -TPR), X-ray diffraction (XRD), N 2 -adsorption specific surface area measurements (BET), CO uptake, transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS). With sample of initial P/Ni molar ratio >0.5, the Ni 2 P was successfully obtained at lower reduction temperature, and a high initial P/Ni molar ratio favors the formation of Ni 2 P at lower temperature. Using less oxidic phosphorus precursor of hypophosphite enabled the Ni 2 P to be formed at low reduction temperature. Evaluation of the activity for DBT HDS of the catalysts shows that the catalyst prepared with initial P/Ni ratios of 2 exhibited the highest activity. At a reaction temperature of 613 K, a pressure of 3.0 MPa, a H 2 /oil ratio of 500 (V/V), and a weight hourly space velocity (WHSV) of 2.0 h −1 , the HDS conversion reached 99%, and no catalyst deactivation was observed within 120 h.

Microwave-assisted catalysis by iron oxide nanoparticles on MCM-41: Effect of the support morphology

Abstract: Catalytically active heterogeneous catalysts have been prepared via microwave deposition of iron oxide nanoparticles (0.5–1.2 wt%) on MCM-41 type silica materials with different morphologies (particles, helical and spheres). This methodology leads to iron oxide nanoparticles composed by a mixture of FeO and Fe2O3 species, being the Fe(II)/Fe(III) peak ratio near to 1.11 by XPS. DRUV spectroscopy indicates the presence of tetrahedral coordinated Fe3+ in the silica framework of the three catalysts as well as some extraframework iron species in the catalysts with particle and sphere-like morphologies. The loading of the nanoparticles does neither affect the mesopore arrangement nor the textural properties of the silica supports, as indicated by SAXS and nitrogen adsorption/desorption isotherms. A detailed investigation of the morphology of the supports in various microwave-assisted catalyzed processes shows that helical mesostructures provide optimum catalytic activities and improved reusabilities in the microwave-assisted redox (selective oxidation of benzyl alcohol) catalyzed process probably due to a combination of lower particle size and higher acidity in comparison with the supports with particle and sphere morphology.

Liquid Hydrocarbon Fuels from Catalytic Cracking of Waste Cooking Oils Using Basic Mesoporous Molecular Sieves K2O/Ba-MCM-41 as Catalysts

Abstract: Mesoporous molecular sieves K2O/Ba-MCM-41, which feature base sites, were prepared under hydrothermal conditions. The structure, base properties, and catalytic activity of the mesoporous molecular sieves as heterogeneous catalysts for the cracking of waste cooking oil (WCO) were then studied in detail. K2O/Ba-MCM-41 exhibited higher catalytic performance for the cracking of WCO than traditional base catalysts such as Na2CO3 and K2CO3. Moreover, the cracking of WCO generates fuels (main composition is C12∼C17 alkane or olefin) that have similar chemical compositions to diesel-based fuels, and K2O/Ba-MCM-41 is of excellent stability. The catalyst could be recycled and reused with negligible loss in activity for four cycles. K2O/Ba-MCM-41 is an environmentally benign heterogeneous basic catalyst for the production of liquid hydrocarbon fuels from low quality feed stocks.

Gold(III) stabilized over ionic liquids grafted on MCM-41 for highly efficient three component coupling reactions

Abstract: Two alkoxysilyl-modified ionic liquids (ILs) have been synthesized and further grafted onto mesoporous silica, MCM-41; these ionic liquids were used for dispersing AuCl3 catalysts that activate C–H bonds as required for the synthesis of propargylamines by coupling alkyne, aldehyde and amine (A3 coupling) species. 29Si NMR experiments demonstrate the formation of covalent bonds between alkoxysilyl-modified Bmim IL and the MCM-41 surface through silanol groups. The catalytic activities of Au(III)-supported MCM-41 and Au(III) homogeneous catalysts are lower than those obtained for the IL functionalized Au–MCM-41 solids when the same gold loading is considered. An interaction between Au(III) species and the IL is proposed for explaining the stabilization of gold(III) species. However, successive reaction cycles result in a decrease in the catalytic activity that has been explained on the basis of gold leaching.

Influence of the synthesis conditions on the physicochemical properties and acidity of Al-MCM-41 as catalysts for the cyclohexanone oxime rearrangement

Abstract: a b s t r a c t Al-containing mesoporous catalysts with MCM-41 structure and high surface area have been success- fully prepared by direct hydrothermal synthesis. Various characterization techniques including XRD, N2 adsorption, ICP-OES, NMR, FT-IR and adsorption of pyridine coupled to FT-IR spectroscopy were employed. A detailed study about the relationships existing between the different synthesis parame- ters, the physico-chemical properties, the acid behavior and the catalytic performance is presented in this contribution. We have suggested that the active sites for the Beckmann rearrangement of cyclo- hexanone oxime are nest silanols (at structural defects) of very weak Bronsted acid character, which is associated with the introduction of Al into the mesoporous framework. In all the cases, employing soft reaction conditions, we have obtained selectivity to caprolactam of 100%. Finally, a Si/Al initial molar ratio of 20, a stirring of synthesis gel for 7 h and a hydrothermal treatment of 6 days seem to be the optimum synthesis conditions to obtain the highest framework Al incorporation, more abundant weak acid sites (silanol nests) and maximum yield for -caprolactam.

Synthesis of 4H-benzo[b]pyrans in the presence of sulfated MCM-41 nanoparticles as efficient and reusable solid acid catalyst

Abstract: A one-pot three-component reaction of various types of aldehydes, dimedone, and malononitrile was studied in the presence of sulfated MCM-41 (SO4 2−/MCM-41) nanoparticles for the synthesis of 4H-benzo[b]pyrans. MCM-41 was synthesized in nanosize by the sol–gel method and then SO4 2−/MCM-41 samples with different calcination temperatures were prepared and characterized by XRD, FT-IR, SEM, and BET techniques. The characterization results show the insertion of sulfate in the mesoporous structure of MCM-41 and the catalytic performance experiments show that SO4 2−/MCM-41 with a calcination temperature of 550 °C has the best catalytic activity. The reusability experiments show that the catalyst is reusable with moderate decrease in activity.

Copper(I)‐N2S2‐salen type complex covalently anchored onto MCM‐41 silica: an efficient and reusable catalyst for the A3‐coupling reaction toward propargylamines

Abstract: The immobilization of copper complexes by covalent anchoring of the ligand on the surface of mesoporous MCM-41 has been described. Bis[2-(phenylthio)benzylidene]-1,2-ethylenediamine as a new N2S2 donor salen-type ligand was covalently anchored onto nanopores of MCM-41 coordinated with copper (I) halide. The organic–inorganic hybrid material was achieved readily using 3-mercaptopropyltrimethoxysilane as a reactive surface modifier. 2-Nitrobenzaldehyde was reacted smoothly with the thiol moieties in order to form functionalized nanoporous silica with carbaldehyde groups. The resulting supported organic moieties were converted to thiosalen ligand and coordinated with CuX (X = CN, Cl, Br, I). Characterization of the heterogeneous catalyst by X-ray diffraction, N2 sorption, FT-IR, diffuse reflectance UV-visible and TGA techniques indicated successful grafting of the copper complex inside the nano-channels of MCM-41. The heterogenized catalyst was evaluated by the Mannich condensation reaction of aldehydes, amines and alkynes. In this reaction, the corresponding propargylamines were obtained as single products in good to excellent yields. Factors such as reaction temperature, solvent, catalyst loading, leaching and reusability of the catalyst also were discussed. The use of MCM-41 as support permits an easier separation and recycles with only a marginal decrease in reactivity. Copyright © 2013 John Wiley & Sons, Ltd.

One-step room-temperature synthesis of [Al]MCM-41 materials for the catalytic conversion of phenylglyoxal to ethylmandelate

Abstract: Mesoporous MCM-41 materials are silica-based systems with hexagonally arranged mesopores with long-range order, which were initially developed in 1992. Generally, the ordered mesopores are formed through the condensation of silicates around the self-assembled micelles by surfactant molecules or through liquid-crystal phases influenced by the silicate. During the past decades, numerous routes for the synthesis of MCM-41 materials have been developed. With modification of the synthesis conditions, such as the type of solvents, silica sources, addition of other metal species (e.g. , Al), surfactant type and relative concentration, pH value, synthesis temperature, aging and drying conditions, etc. , the morphology and catalytic properties of the obtained MCM-41 materials can be controlled. Among them, the direct room-temperature synthesis of siliceous MCM-41 f, h,4] has drawn great interest as it is a rapid method under mild conditions with less energy and time consumed compared with classic hydrothermal synthesis (heating normally required at 60–150 8C for 1–6 d). 5] Huo et al. synthesized mesoporous silica spheres by using different silica sources under basic conditions with stirring for 15–30 h at room temperature. They found that lower alkoxysilanes, such as tetramethyl orthosilicate (TMOS) and tetraethyl orthosilicate (TEOS), yielded only small MCM-41 particles, whereas higher alkoxysilanes, such as tetrabutyl orthosilicate (TBOS), led to larger MCM-41 spheres. These spheres were obtained at a low stirring speed ( 450 rpm). Cai et al. and Grun et al. synthesized siliceous MCM-41 particles in a diluted solution of surfactants with tetraethoxysilane under basic conditions at room temperature with stirring for 2 h. The resulting particle size was in the range of micrometers (1 mm) to nanometers (100 nm) controlled by using different basic additives (NaOH/NH4OH) [3c] and surfactants (n-hexadecyltrimethylammonium bromide and nhexadecylpyridiniumchloride monohydrate). Recently, Pescarmona and co-workers synthesized [Ti]MCM-41 materials with particle sizes of 80–160 nm by using TEOS, cetyltrimethylammonium bromide (CTAB), NaOH, and titanium(IV) isopropoxide with stirring at room temperature for 2 h and found that Mesoporous [Al]MCM-41 materials with nSi/nAl ratios of 15 to 50 suitable for the direct catalytic conversion of phenylglyoxal to ethylmandelate have been successfully synthesized at room temperature within 1 h. The surface areas and pore sizes of the obtained [Al]MCM-41 materials are in the ranges of 1005– 1246 mg 1 and 3.44–3.99 nm, respectively, for the different nSi/nAl ratios. For all [Al]MCM-41 catalysts, most of the Al species were tetrahedrally coordinated with Si in the next coordination sphere of atoms. H and C magic-angle spinning NMR spectroscopic investigations indicated that the acid strength of the SiOH groups on these [Al]MCM-41 catalysts and the density of these surface sites are enhanced with increasing Al content in the synthesis gels. These surface sites with enhanced acid strength were found to be catalytically active sites for phenylglyoxal conversion. The [Al]MCM-41 material with nSi/ nAl=15 showed the highest phenylglyoxal conversion (93.4%) and selectivity to ethylmandelate (96.9%), whereas the [Al]MCM-41 material with nSi/nAl=50 reached the highest turnover frequency (TOF=99.3 h ). This is a much better catalytic performance than that of a dealuminated zeolite Y (TOF= 1.7 h ) used as a reference catalyst, which is explained by lower reactant transport limitations in mesoporous materials than that in the microporous zeolite.

Air stable ligandless heterogeneous catalyst systems based on Pd and Au supported in SiO2 and MCM-41 for Suzuki–Miyaura cross-coupling in aqueous medium

Abstract: Palladium and palladium-gold containing siliceous-MCM-41 and sol–gel palladium and palladium-gold silica composites have been prepared. The catalytic performance of incorporated Pd/MCM-41, Au-Pd/MCM-41 and Pd and Au-Pd/SiO2 sol–gel catalysts for the Suzuki–Miyaura cross-coupling reaction was determined and the influence of the matrix and the catalyst composition on the catalytic activity were also studied. The catalysts were characterized by N2 physisorption (BET/BJH methods), X-ray diffraction, temperature programmed reduction analysis, H2 chemisorption, atomic absorption spectrophotometry and Raman spectroscopy. The silica-containing palladium and palladium-gold catalysts prepared using the MCM-41 matrix showed greater catalytic activity than using the conventional sol–gel method; however, gold had a significant influence on this reaction. The catalyst did not undergo metal leaching and could be easily recovered and re-used (reused).