Solid mesoporous materials

The TS-l/MCM-41 catalysts were synthesized in two steps [8]. The first step was involved with the preparation of TPAOH impregnate mesoporous materials and the second stq) was the DGC process. The TPAOH impregnated H-MCM-41 was prepare with calcine Ti-MCM-41, TPAOH (1 M solution of water) and ethanol under stirring by impregnation method. The parent gels were prepared with a TPAOH/Ti-MCM-41 ratio of 1/3 by weight. After 4 h, ethanol and water were removed in a rotary evaporator at room temperature and solid products were dried in a convention oven at 373 K for 48 h. The DGC process was carried out at 448 K for 3 h to obtain TS-1/MCM-41-A and for 6 h to obtain TS-1/MCM-41-B. However, the mesoporosity of Ti-MCM-41 was lost when the DGC process was carried out for 9 h. 

Zeolites form a class with tremendous variety. Besides the microporous solids described in the above, mesoporous materials have been synthesized. A breakthrough were the MCM-41 mesoporous zeolites with pores of typically 3 nm. Later, many related materials have been reported allowing fine-tuning of pore sizes. A recent example is the synthesis of materials with pores in the lOnm range with satisfactory uniformity and stability (Sun etai, 2001). 

In order to overcome these problems, attention was focused on the use of heterogeneous catalysis. We have found that functionalized solid materials, e.g., ionic liquids or tin triflates immobilized into mesoporous materials, can be used in N-acylation reactions as environmentally friendly replacements for traditional homogeneous acids which are useful but environmentally unacceptable catalysts [17, 18]. They had comparable activity to homogeneous reagents but can offer greater stability, safer and easier handling and can be... 

Microporous nanoparticles with ordered zeolitic structure such as Ti-Beta are used for incorporation into walls or deposition into pores of mesoporous materials to form the micro/mesoporous composite materials [1-3], Microporous particles need to be small enough to be successfully incorporated in the composite structure. This means that the zeolite synthesis has to be stopped as soon as the particles exhibit ordered zeolitic structure. To study the growth of Ti-Beta particles we used 29Si solid-state and liquid-state NMR spectroscopy combined with x-ray powder diffraction (XRPD) and high-resolution transmission electron microscopy (HRTEM). With these techniques we monitored zeolite formation from the initial precursor gel to the final Ti-Beta product. 

Mesoporous materials (SBA-15 and Al-SBA-15 with various Si/Al ratios) were synthesized and investigated in relation to their capacity to be used as adsorbents for depollution of the contaminated air or wastewater. The compositional and the structural properties were determined by XRD, N2 isotherms, NMR, chemical analysis and XPS. The acidity and adsorption properties of the solids were checked by adsorption microcalorimetry using various basic or polluting molecules in gas phase. 

Keywords Catalysis Mesoporous materials Solid state NMR Zeolites 27A1 ... 

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... 

Pores are found in many solids and the term porosity is often used quite arbitrarily to describe many different properties of such materials. Occasionally, it is used to indicate the mere presence of pores in a material, sometimes as a measure for the size of the pores, and often as a measure for the amount of pores present in a material. The latter is closest to its physical definition. The porosity of a material is defined as the ratio between the pore volume of a particle and its total volume (pore volume + volume of solid) [1]. A certain porosity is a common feature of most heterogeneous catalysts. The pores are either formed by voids between small aggregated particles (textural porosity) or they are intrinsic structural features of the materials (structural porosity). According to the IUPAC notation, porous materials are classified with respect to their sizes into three groups microporous, mesoporous, and macroporous materials [2], Microporous materials have pores with diameters < 2 nm, mesoporous materials have pore diameters between 2 and 50 nm, and macroporous materials have pore diameters > 50 nm. Nowadays, some authors use the term nanoporosity which, however, has no clear definition but is typically used in combination with nanotechnology and nanochemistry for materials with pore sizes in the nanometer range, i.e., 0.1 to 100 nm. Nanoporous could thus mean everything from microporous to macroporous. 

Gas adsorption (physisorption) is one of the most frequently used characterization methods for micro- and mesoporous materials. It provides information on the pore volume, the specific surface area, the pore size distribution, and heat of adsorption of a given material. The basic principle of the methods is simple interaction of molecules in a gas phase (adsorptive) with the surface of a sohd phase (adsorbent). Owing to van der Waals (London) forces, a film of adsorbed molecules (adsorbate) forms on the surface of the solid upon incremental increase of the partial pressure of the gas. The amount of gas molecules that are adsorbed by the solid is detected. This allows the analysis of surface and pore properties. Knowing the space occupied by one adsorbed molecule, Ag, and the number of gas molecules in the adsorbed layer next to the surface of the solid, (monolayer capacity of a given mass of adsorbent) allows for the calculation of the specific surface area, As, of the solid by simply multiplying the number of the adsorbed molecules per weight unit of solid with the space required by one gas molecule ... 

In the following section, we restrict our discussion to templated mesoporous solids that are of potential interest as battery electrodes, including many transition-metal oxides and carbon. This slice of the literature still points the interested reader to many articles on the synthesis and physical characterization of relevant mesoporous materials. A much smaller number of electrochemical studies with templated mesoporous electrodes have been published, and these studies in particular will be noted. 

Fig. 1. Nitrogen adsorption-desorption isotherms at -196 C for the mesoporous material OH-02-600 and its precursory synthetic hectorite H-02-300. Open symbols adsorption. Solid symbols desorption.

The mesoporous solids have great potential for use as heterogeneous catalysts, which have the advantage of being simpler to use than homogeneous catalysts as they can be separated by filtration at the end of a reaction. A great deal of research has gone into various modifications of the structure to make them suitable for particular reactions. The aluminosilicate walls of mesoporous materials can be modified in various ways ... 

The silica forms of MCM-41, MCM-48, KIT-1, HMS, and SBA-1 were prepared by hydrothermal synthesis following the methods reported in the literature [1,2,3,4,7]. The calcined mesoporous materials were slurried in absolute isopropyl alcohol solution containing TIPOT (10wt%) with magnetic stirring at room temperature for 3h. The solid products obtained were then washed with absolute isopropyl alcohol, dried and calcined in air at 823K... 

Synthesis of solid state materials using surfactant molecules as template has been extensively used in this decade. Among the advantages of the use of amphiphilic molecules, the self-assembling property of the surfactants can provide an effective method for synthesising ceramic and composite materials with interesting characteristics, such as nanoscale control of morphology, and nano or mesopore structure with narrow and controllable size distribution [1-5]. 

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