Mesoporous solids structure determination

The main properties of these materials were characterized by means of x-ray diffraction (Siemens D-500 with A.Cu radiation of 1.54 A), Transmission Electron Microscopy (Phillips-CM200) and N2 adsorption (Micromeritics ASAP-2000), 29Si-NMR(MAS). As the textural properties of the catalytic materials, for example the inner pore structure, is a key parameter for their performance, in the present work the N2 adsorption isotherms of the calcined mesoporous Si02-based solids were determined. The solids were prepared using different CTAB surfactant and some co-surfactants based in the light alcohols, i.e. MeOH, EtOH and PrOH. Thus, Figure 15.5 shows the isotherms of the mesoporous solids prepared with MeOH (co-surfactant). In all... 

Consider a sorption experiment, where a mesoporous solid, denoted hereafter as S, is progressively loaded by a condensable gas or vapour. Initially, a layer of adsorbate L is building up on the walls of the pores. When condensation occurs, all the pores with radii smaller than a critical value, given by the Kelvin equation, are progressively blocked, and the adsorbate is in equilibrium with its vapour, V. The distribution of the condensed phase in a reconstructed Vycor structure for a given degree of pore filling (saturation), is determined by... 

The Type IVa isotherm is given by a well-defined mesoporous solid having a fairly narrow distribution of pore size. In the monolayer and initial multilayer region (i.e. up to p/p 0.4) this isotherm follows the same path as the corresponding Type Ila isotherm determined on the equivalent area of a non-porous surface of similar structure. In this case capillary condensation is responsible for the upward deviation of the isotherm in the multilayer region. Such isotherms are obtained only with those mesoporous solids having uniform pore structures. 

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. 

Many reactions taking place within catalyst or absorbent pellets in industrial plants are diffusion-limited. Under the typical operating conditions for many absorbents, diffusion of gases into the porous solid occurs in the Knudsen regime. In such circumstances the rate of gas pick-up of these materials is strongly dependent on the pore structure. The pore structure for absorbent pellets that will deliver the most efficient operation of an absorbent bed requires a pervasive system of macropores which provide rapid transport of the gas flux into the centre of the pellet. A network of ramified mesopores branching off the macropores then provides extensive surface area for absorption of gas molecules. Therefore, when manufacturing an absorbent it is necessary to be able to determine the spatial distribution of the macropore network in a product to ensure that the pore structure is the most appropriate for the peirticular duty for which it is intended. 

Presented are the examinations of the multifimctional mineral-earbon and zeolite-carbon sorbents prepared from kaolinite with an admixture of carbonaceous materials industrial waste deposits, municipal sewage sludge and cellulose. The mixture of raw materials was thermally and hydrothermally pretreated in order to facilitate their specific structure. The parameters of capillary structure (micro and mesopores) were determined. For examinations of porous structure the mereury porosimetry method was used. In order to evaluate the solid phase transformation during the each step of sorbent preparation the SEM observation with quantitative X-ray mieroanalysis were made. 

Curved structures are not only limited to carbon and the dichalcogenides of Mo and W. Perhaps the most well-known example of a tube-like structure with diameters in the nanometer range is formed by the asbestos mineral (chrysotil) whose fibrous characteristics are determined by the tubular structure of the fused tetrahedral and octahedral layers. The synthesis of mesoporous silica with well-defined pores in the 2-20 nm range was reported by Beck and Kresge [215]. The synthetic strategy involved the self-assembly of liquid crystalline templates. The pore size in zeolitic and other inorganic porous solids is varied by a suitable choice of the template. However, in contrast to the synthesis of porous compounds, the synthesis of nanotubes is somewhat more difficult. 

Another SILP catalyst used under batch conditions employed mesoporous MCM-41 as the solid support. The catalyst was derived from [Rh(CO)2(acac)] and TPPTS (1 5 mol ratio) in the desired IL. The excellent catalytic performance of this SILP catalyst in the hydroformylation of C6-C12 linear alkenes (TOF up to 500 h ) was determined by the large surface area and uniform mesopore structure of MCM-41 and was almost independent of the type of IL used [bmim][BF4], [bmim][PF6] and 1,1,3,3-tetramethylguanidinium lactate. 

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