Micelle templating

Stack and coworkers immobilized phenantrohne derivative 16 on micelle-templated silica SBA-15 (Scheme 8) [55,56]. The system showed more selective and efficient catalytic activity for olefin epoxidations with peracetic acid than the analogous homogeneous catalyst. 

Most examples discussed so far made use of amorphous inorganic supports or sol-gel processed hybrid polymers. Highly disperse materials have recently become accessible via standard processes and, as a result, materials with various controlled particle size, pore diameter are now available. Micelle-templated synthesis of inorganic materials leads to mesoporous materials such as MCM-41, MCM-48, MSU, and these have been extensively used as solid supports for catalysis [52]. Modifications of the polarity of the material can increase the reactivity of the embedded centre, or can decrease its susceptibility to deactivation. In rare cases, enhanced stereo- or even... 

Figure 9.1. Scheme of micelle templating. The circular objects correspond to micelles and the gray color to the condensed inorganic oxide network. 

Similarly, Hg(n) binding to thiol-functionalized mesoporous silica for which effective access to all the binding sites (100% of SH groups com-plexed with Hg(n) was achieved in micelle-templated mesostructures with pore diameters larger than 2.0 nm, whereas incomplete filling was always observed with corresponding amorphous silica-based adsorbents.37... 

Ordered mesoporous materials of compositions other than silica or silica-alumina are also accessible. Employing the micelle templating route, several oxidic mesostructures have been made. Unfortunately, the pores of many such materials collapse upon template removal by calcination. The oxides in the pore walls are often not very well condensed or suffer from reciystallization of the oxides. In some cases, even changes of the oxidation state of the metals may play a role. Stabilization of the pore walls in post-synthesis results in a material that is rather stable toward calcination. By post-synthetic treatment with phosphoric acid, stable alumina, titania, and zirconia mesophases were obtained (see [27] and references therein). The phosphoric acid results in further condensation of the pore walls and the materials can be calcined with preservation of the pore system. Not only mesoporous oxidic materials but also phosphates, sulfides, and selenides can be obtained by surfactant templating. These materials have pore systems similar to OMS materials. 

Fig. 9 Schematic representation of three approaches to generate nanoporous and meso-porous materials with block copolymers, a Block copolymer micelle templating for mesoporous inorganic materials. Block copolymer micelles form a hexagonal array. Silicate species then occupy the spaces between the cylinders. The final removal of micelle template leaves hollow cylinders, b Block copolymer matrix for nanoporous materials. Block copolymers form hexagonal cylinder phase in bulk or thin film state. Subsequent crosslinking fixes the matrix hollow channels are generated by removing the minor phase, c Rod-coil block copolymer for microporous materials. Solution-cast micellar films consisted of multilayers of hexagonally ordered arrays of spherical holes. (Adapted from [33])...

D. Brunei, N. Bellocq, P. Sutra, A. Cauvel, M. Lasperas, P. Moreau, F. Di Renzo, A. Galarneau, and F. Fajula, Transition-metal ligands bound onto the micelle-templated silica surface. Coord. Chem. Rev. 180, 1085-1108 (1998). 

Di Renzo, F., Cambon, H., and Dutarte, R. (1997) A 28-year-old synthesis of micelle-templated mesoporous silica. Microporous Mater., 10, 283-286 Chiola, V., Ritsko, J.E., and Vanderpool, C.D. (1971) Process for producing low-bulk density silica. US Patent 3,556,725, assigned to Sylvania Electric Products, Inc. 

Spherical particles in the micrometric size range of mesoporous MSU-X silica were obtained with nonionic PEO-based surfactant by a new, easy and highly reproducible synthesis pathway leading to Micelle Templated Structures (MTS) with large surface area and narrow pore size distribution. First results on their adsorption properties show that they could be used for HPLC applications. 

The mechanical properties of Micelle-Templated Silicas (MTS) are very sensitive items for industrial process applications which might submit catalysts or adsorbents to relevant pressure levels, either in the shaping of the solid or in the working conditions of catalysis or separation vessels. First studies about compression of these highly porous materials have shown a very low stability against pressure. These results concern these specific materials tested. In this study, we show very stable MTS with only a loss of 25% of the pore volume at 3 kbar. The effects of several synthesis parameters on the mechanical strength are discussed. 

Since the disclosure by Mobil of Micelle-Templated Silicate structures called MCM-41 (hexagonal symmetry) or MCM-48 (cubic symmetry) [1,2] many other structures have been synthesized using different surfactants and different synthesis conditions. All of these Micelle-Templated Silicas (MTS) have attracted much interest in fields as diverse as catalysis, adsorption, waste treatment and nanotechnology. MTS materials possess a high surface area ( 1000 m2/g), high pore volume ( 1 mL/g), tunable pore size (18-150 A), narrow pore size distribution, adjustable wall thickness (5-20 A). The silica walls can be doped with different metals for catalytic applications, like Al orTi, for acidic or oxydation reactions, respectively. 

Hence, in this work, we report the heterogeneization of this new chiral macrocycle onto micelle-templated silicate (MTS) surface by substitution of chlorine atom of previously grafted 3-chloropropyl chain. After A-alkylation of the tetraazamacrocycle with propylene oxide and metalation with Mn(lI)Cl2, the catalytic performance of the corresponding hybrid materials was evaluated in the heterogeneous enantioselective olefin epoxidation. 

A new optically active tetraazamacrocycle ligand, 27 ,37 -cyclohexano-1,4,7,10-tetra-azacyclododecane was covalently anchored on micelle-templated silicate (MTS) surface. The... 

Even though there is great interest in such systems based on polymers as supporting materials, this chapter essentially focuses on the use of minerals as support. The use of silica has been historically investigated, mainly for its large surface area. As mentioned later, micelle-templated silica (MTS) has recently been disclosed. 

Hybrid Mesoporous Micelle-templated Silicas (MTS) Containing Organic Base Moieties... 

Brunei, D. Functionalized micelle-templated silicas (MTS) and their use as catalysts for fine chemicals. Microporous Mesoporous Mater., 1999, 27, 329-344. 

Derrien, A., Renard, G. and Brunei, D. Guanidine linked to micelle-templated mesoporous silicates as base catalyst for transesterification. Stud. Surf. Sci. Catal., 1998,117, 445-452. 

Sutra, P., Fajula, F., Brunei, D., Lentz, P., Daelen, G. and Nagy, J. B. Si-29 and C-13 MAS-NMR characterization of surface modification of micelle-templated silicas during the grafting of organic moieties and end-capping, Colloids Surf., A, 1999, 158, 21-27. 

Zr-containing mesoporous silicas offer some potential for the oxidation of aniline with H2O2 as the oxidant. The Zr is introduced as Zr(OiPr)4 during the micelle-templated hydrothermal synthesis of the MCM-41-type structure (206). The materials are calcined prior to use in catalytic experiments. Azobenzene and azoxybenzene are formed ... 

The UV-visible absorption spectrum of the CdS nanotubes given in Fig. 2a shows a blue-shift in the excitonic absorption band to 460 nm. The blue-shift from the bulk value of 515 nm [12] is due to quantum confinement effects in the CdS nanotubes, the inner diameter of the nanotubes being less than the Bohr-exciton diameter of CdS (6 nm). Xiong et al. [13] have reported an absorption band at 459 nm for CdS nanotubes with an inner diameter 5 nm prepared by an in situ micelle-template-interface reaction. An absorption maximum around 450 nm has been reported in nanoparticles and hollow spheres of CdS [12,14], In Fig. 2b, we show the photoluminescence (PL) spectrum of the CdS nanotubes prepared by us, revealing a band centered at 610 nm. This band is due to charge carriers trapped at surface defects of the nanotubes [15,16],... 

Some degree of success in supported enantioselective catalysis was accomplished by using functionalisation of mineral support. Due to their unique textural and surface properties, mesoporous micelle-templated silicas are able to bring new interesting properties for the preparation of optically active solids. Many successfully examples have been reported for enantioselective hydrogenation, epoxidation and alkylation. However, the stability of the immobilised catalysts still deserves efforts to allow industrial development of such attractive materials. 

In this work, the synthesis of high surface densities of chlororopropyl groups covalently grafted on mesoporous micelle templated aluminosilicates (Al-MTS) of various initial pore diameters is presented. The hybrid chiral materials resulting from halogen substitution are applied in the enantioselective addition of diethylzinc to benzaldehyde. 

An other approach was followed with a micelle-templated silica of the MCM-41 type. These mesoporous carriers were first grafted with the chlorosilane 7 and then aminated with a guanidine such as TBD 2 11 (Figure 8). 

GUANIDINE CATALYSTS SUPPORTED ON SILICA AND MICELLE TEMPLATED SILICAS. NEW BASIC CATALYSTS FOR ORGANIC CHEMISTRY... 

Guanidine Catalysts Supported on Silica and Micelle Templated Silicas... 

Fig. 2.10 Synthesis of mesoporous, micelle-templated molecular sieves.

Fig. 2.40 Methods for attachment of organic bases to micelle templated silicas.

Huang H, Remsen EE, Kowalewski T, Wooley KL (1999) Nanocages derived from shell cross-linked micelle templates. J Am Chem Soc 121(15) 3805-3806... 

Cauvel, A., Brunei, D., and Di Renzo, F., Hydrophobic and hydrophilic behavior of micelle-templated mesoporous silica, Langmuir, 13, 2113, 1997. 

Fig. 24 Schematic illustration of the synthetic pathway for hoUow square particles derived from polysilane shell cross-Unked micelles templates. Reproduced with permission from [50] Sanji et al. (2000) Macromolecules 33 8524. American Chemical Society...

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