Mesoporous materials synthesis parameters

The synthesis procedure for mesoporous material is simple, and synthesis parameters can be controlled easily. The simple procedure does not mean that the reactions or interactions among reactants in the synthesis system are simple. Many complicated reactions, interactions, and assemblies occur in the mesoporous material synthesis system. The synthesis involves three main components Inorganic species for the formation of the inorganic wall template (surfactant in most cases) whose assembly will guide the formation of mesophase the reaction media (solvent). Figure 8.3 shows the interactions between the three main components.[59] These interactions play the key roles during synthesis. The surfactant molecules in the solution will self-assemble into a micelle or liquid-crystal phase of course, various factors can affect the assembly process,... 

It is important to emphasize that the situations described above are different synthesis strategies that expectedly lead to composite and porous materials that have distinctly different properties. In the preparation of mesoporous materials, procedural variables define a very complex system in which kinetic parameters (time, basic operations sequence) may play a determinant role. 

Alumina and amorphous silica-alumina are usually mesoporous materials with a wide distribution of pore sizes. The surface area, pore size and pore volume of alumina and amorphous silica-alumina depend greatly on the preparation method, hence their textural properties can be controlled to a certain extent by changing the synthesis conditions. These parameters are also highly relevant in determining the catalytic properties of these materials. 

A comparison study on the synthesis of mesoporous materials from Triton X-lOO/Na-metasilicate and CTAB/TEOS was performed and their textural and structural parameters were characterized by XRD, N2 adorption and TEM. The CTAB/TEOS solids presented high surface mesopore areas, exceeding 1100 m /g, while the Triton X-lOO/Na-metasilicate presented areas from 1200 up to 1467 m /g. The analysis of the textural data indicated that upon calcination pore sintering occurs in the Triton /Na-metasilicate solids, while it does not occurs in the CTAB/TEOS system. This is probably due to the different packing effective factor of the surfactant molecules. 

Titanium has also been incorporated into ordered mesoporous silicas of the SBA-15 type (126). The influence of synthesis parameters on the properties of titanium-substituted SB A-15 silicas prepared by a direct one-step synthesis (cocondensation) was systematically investigated (127) through characterizing the products by N2 physisorption, XRD, diffuse reflectance UV-vis spectroscopy, and elemental analysis. The results showed that when a low titanium precursor concentration (i.e., less than 0.05 mol/1) was used in the initial synthesis gel, incorporation of titanium into the solid was not completed. Under these conditions, titanium ions were well dispersed in the silica framework and present mainly in tetrahedral coordination in the product. When the isolated titanium species present in the gel reached a critical concentration, an increase in titanium incorporation into the sofid was observed as a consequence of the formation of anatase clusters on the material s surface. The titanium loading at which anatase formation was observed was found to he strongly influenced by the synthesis conditions. Moreover, when the formation of anatase takes place, the amorphous titanium species... 

MCM-41 is the well known model mesoporous material containing extended hexagonal arrays of parallel tubular pores separated by amorphous silica (Fig. 1.). This is a common description, on the heise of most studies to interpret adsorption phenomenon results. However, the structural and chemical parameters of the host porous material have a crucial influence on the adsorption mechanism. Actually each synthesis produces MCM-41 sample with its own silica wall and porosity. Our MCM-41 (19 A < 0 < 40 A) samples have been extensively characterized by sorption isotherm, microcalorimetry and neutron diffraction measurements... 

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