Mesoporous ordered

The mesoporous ordered silicas of different type represent the new generation of materials with unique properties. The discovery of these materials became basis for creation of new catalysts, adsorbents, sensors and supporter for other molecules. The most important way of the modifying physical and chemical properties of mesopurous silicas consist in organic components incorporation on the silica surface as part of the silicate walls or their insertion within channels of the mesopores. This ensured that interest in synthesis and study of functionalized mesoporous materials shai ply grew. In spite of it, these materials are studied insufficiently. 

Grosso, D. Boissiere, C. Nicole, L. Sanchez, C. 2006. Preparation, treatment and characterisation of nanocrystalline mesoporous ordered layers. /. Sol-Gel Sci. Technol. 40 141-154. 

Several examples exist of the application of chiral natural N-compounds in base-catalyzed reactions. Thus, L-proline and cinchona alkaloids have been applied [35] in enantioselective aldol condensations and Michael addition. Techniques are available to heterogenize natural N-bases, such as ephedrine, by covalent binding to mesoporous ordered silica materials [36]. 

All of these mesoporous materials are characterized by having narrow pore size distributions comparable to microporous materials, and extraordinary hydrocarbon sorption capacities. These materials are important mostly because of their exceptional ordered mesopore structure, which is not common for other adsorbent materials. As a result, mesoporous-ordered silica has been proposed as a reference material for the study of adsorption processes in mesopores [16]. 

For this reason, recent attention has been dedicated to micro- and meso-porous materials (MMM), and also for their possible use as shape-selectivity controlled reactions (space-restricted transition states, preferential diffusion and back-diffusion). Even if the latter aspects are better known regarding the performances of microporous materials, other aspects can be evidenced. In fact, also in mesoporous materials, where the dimensions of the channels are larger, as required for shape-selectivity effects, a change of reactivity of molecules inside the channels could be present due to confinement effects [281]. Therefore, the catalytic reactivity shown by basic sites located inside mesoporous channels could differ from that of the same sites located instead on the external surface of the mesoporous ordered material. 

Vapor-phase epoxidation of propylene using H2 and O2 was carried out over gold catalysts supported on mesoporous ordered (MCM-41) and disordered titanosilicates prepared hydrothermally or by modified sol-gel method. Gold nanoparticles were homogeneously dispersed on the titanosilicate supports by deposition-precipitation (DP) method. The catalysts and support materials were characterized by XRD, UV-Vis, surface area measurements (N2 adsorption) and TEM. NaOH was found to be the best precipitant to prepare Au catalysts with optimum propylene oxide yields and H2 efficiency. The extent of catalysts washing during preparation was found to affect the activity of the catalyst. The activity and hydrogen efficiency was found to depend on the type of mesoporous support used. 

The synthesis and characterization of a mesoporous silicoalumino phosphate are given employing typical structure directing reagent viz. cetyltrimethyl ammonium bromide. The Si MAS NMR showed that silicon is found in coordination with 1, 2, 3 and 4 A1 ions through oxygen bridges. The sorption characteristics of this new mesoporous SAPO material are also presented. Keywords Silico aluminophosphate, Mesoporous, ordered molecular arrays, MAS NMR. 

Figure 2. Grafting and coating of a mesoporous ordered Si02 with mercaptopropyl groups (R = Me, Et).

SBA-15 is a mesoporous ordered silica with promising properties as a catalyst support [1], where functionalization of the siliceous carrier with an active component can be achieved through a number of methods [2]. In this study we describe the use of the deposition-precipitation technique (DP) employed to functionalize the SBA-15 with Pt. The use of the DP method on the SBA class of materials has not been studied so far, excluding a few studies dealing with deposition of gold on titania-modified SBA-15 [3, 4]. The method... 

A. Diaz, T. Lopez, J. Manjarrez, E. Basaldella, J. M. Martinez-Blanes, J. A. Odriozola Growth of hydroxyapatite in a biocompatible mesoporous ordered silica. Acta Biomaterialia, 2,173 (2006). 

The p (f) vector corresponds to the maximum entropy principle of the/-order. This procedure was used to modify the CONTIN algorithm (CONTIN/MEM-/, where / denotes the order of p (f)). A self-consistent regularization procedure (starting calculations were done without application of MEM) with an unfixed regularization parameter (for better fitting) was used on CONTIN/MEM-/ calculations, which were applied for mesoporous ordered silicas (vide infra). 

Grunenwald, A., Ayral, A., Albouy, P.-A. et al. 2012. Hydrophobic mesostructured organosUica-based thin films with tunable mesopore ordering. Micropor. Mesopor. Mater. 150 64-75. 

Iron-containing mesoporous materials have been widely studied due to the unique catalytic performance of selective reduction, hydrocarbon oxidation, and acylation and alkylation reactions (Vinu et al. 2007). Thus, Tanglumlert et al. (2008) were interested in the room temperature synthesis of Fe-SBA-1 using FeCl3 via the sol-gel process. The results illustrated that up to 6 wt% Fe could be contained in the SBA-1 framework without destroying the mesopore order. Nevertheless, extraframework FeOg clusters were also found, as suggested by electron spin resonance (ESR) spectroscopy. The BET surface area was 1062 m /g, with a pore diameter around 2.1 nm. 

L. Malfatti, et al.. Nanocomposite mesoporous ordered films for lab-on-chip intrinsic surface enhanced Raman scattering detection. Nanoscale 3 (2011) 3760-3766. 

Finally, it has been indicated that the use of mesoporous ordered siUca materials as supports for metal oxides exhibited higher catalytic activity compared to microporous zeolite catalysts for catal3dic combustion of toluene in the presence of excess oxygen, and furthermore coke formation could be effectively minimised. 

LEEB, in fact, supplies highly efficient electron beam into films thinner than 30 pm, allowing a complete modification of their chemical structure. In addition, LEEB emits no infrared rays, and therefore it does not heat the samples, whereas the low electron energy generally prevents irradiation damage to the substrate. This approach has been used to pattern both silica- and titania-based mesoporous ordered films without affecting the pore order and microfebricating squareshaped patterns composed of 25 X 25 pm features over an area of several centimeters [106,107]. 

The possibihty of obtaining nanopartides upon exposure to hard X-rays is not restricted to metallic nanopartides, in fact oxide nanopartides within a mesopo-rous ordered matrix have been also obtained. One example is ceriimi oxide nanopartides within a titania mesoporous ordered film to produce ceria NPs, the titania mesopores have been impregnated with a ceria precursor solution and then exposed to hard X-rays. Crystalline cerium oxide NPs with an average size of 4 nm have been grown within the mesopores, and different patterns with spatial control of the nanoparticle growth on the micrometer scale have been obtained [121]. 

Malfatti, L., Falcaro, P., Marmiroli, B., Amenitsch, H., Piccinini, M., Falqui, A., and Innocenzi, P. (2011) Nanocomposite mesoporous ordered films for lab-on-chip intrinsic surfeice enhanced Raman scattering detection. Nanoscale, 3, 3760-3766. 

Figure 33. HRTEM images of a SrTiOj mesoporous ordered network (a-c) before crystallization, obtained at 590 °C, and (d-e) after crystallization, obtained at 630 °C[233].

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