Micelle templated silica

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. 

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. 

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. 

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. 

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 ... 

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. 

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

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

The present report focuses on the intrusion-extrusion characteristics of grafted silica-based materials conventional chromatography adsorbents and Micelle-Templated-Silica materials (MCM-41) [3]. Finally, the mechanisms of energy dissipation will be analyzed in terms of general thermodynamic considerations. 

In conclusion, the study of the influence of grafted chain length on the hydrophobicity of silica gel allowed us to choose a convenient surface treatment, which was successfully transposed to MCM-41 materials. These former materials were demonstrated to be particularly suitable for the considered new field of applications, and to present advantages compared to silica gels. Finally, Micelle-Templated-Silica materials represent a class of useful models for a comprehensive study of the mechanisms of energy dissipation during forced intrusion and more generally of the physical chemistry of surfaces. 

The overall performance of a catalyst is known to depend not only on the inherent catalytic activity of the active phase but also on the textural properties of the solid. The ability to control the specific surface area and the pore size distribution during the synthesis of amorphous silica-aluminas has been described for both surfactant micelle templated syntheses (M41-S (1), FSM-16 (2), HMS (3), SBA (4), MSU (5), KIT-1 (6)) and cluster templated sol-gel syntheses (MSA (7), ERS-8 (8)). 

Figure 37. Nitrogen adsorption-desorption isotherms of parent mesoporous material MTS (solid line), Cl-MTS (dashed line) and tSalpr-MTS (dotted line). MTS = micelle templated silica, Cl-MTS = MTS modified by 3-chloropropylsilane and tSalpr-MTS = MTS modified with Mn(III) iV,iV -bis[3-(3,5-di-ieri-butylsalicylidenamino)propyl]amine.

M.F. Ottaviani, A. Galarneau, D. Desplantier-Giscard, F. Di Renzo, and F. Fajula, EPR Investigations on the Formation of Micelle-templated Silica. Microporous Mesoporous Mater., 2001, 44, 1-8. 

Galameau, A. et al., Kinetics of formation of micelle-templated silica mesophases monitored by electron paramagnetic resonance, J. Colloid Interface Set, 201, 105, 1998. 

Ottaviani, M.F. et al., EPR investigations on the formation of micelle-templated silica, Microporous Mesoporous Mater., 44, 1, 2001. 

In this respect, the recently discovered family of materials synthetized by silicate condensation around surfactant micelles (Micelle-Templated Silica, MTS) provides unique inorganic support [11,12] due to their regular arrays of uniformly sized channels in the mesopore range of 20-100 A. This solid was recently impregnated with cesium oxides with the aim to obtain superbase catalysts [13]. Nevertheless, the leaching of the basic particles cannot be excluded. In view to avoid such possible phenomena, we have studied the covalent attachment of basic functions such as amino groups on the MTS surface... 

The synthesis and characterization of a chiral amino-alcohol ((1R-2S)-ephedrine) immobilized on MCM-41 type mesoporous silicas (MTS Micelle Template Silicas) are described. The activity of these supported catalysts in the enantioselective addition of diethylzinc to benzaldehyde are reported, and compared with those obtained with the corresponding silica gel supported catalysts. The observed differences are discussed in terms of the nature of the grafting which depends on the support structure. 

The new generation of MCM-41 type mesoporous silicas (MTS Micelle Template Silicas) which are characterized by a regular porosity, consisting of uniformly sized channels with pore diameters within a mesoporous range of 20-100 A [8] have not been used in this type of enantioselective catalysis. Taking into account their characteristic structure, the insertion and grafting of functional molecules is possible as it has been shown recently in this laboratory [9]. 

The time from discovery to process for synthetic zeolites has been about ten years. This lag has already elapsed since the discovery of the ordered mesoporous materials and times seem ripe for their industrial development. The main obstacle towards viable applications is the presence on the market of much cheaper amorphous alternatives, mainly based on silica gels. Micelle-templated materials has to compete for new applications, to obtain results that can be achieved only thanks to their narrow pore size distribution. 

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