Pore mesopores

Chong, A.S.M. and Zhao, X.S. (2004) Design of large-pore mesoporous materials for immobilization of penicillin G acylase biocatalyst. Catalysis Today, 93-95, 293-299. 

Figure 1.31P and 27A1 NMR spectra of F127- and F108-templated large-pore mesoporous... 

Figure 2.31P and 27AI MAS NMR spectra of F127- and FI 08-templated cubic large-pore mesoporous aluminophosphate thin films. 

Yang, P. D. Zhao, D. Y. Margolese, D. I. Chmelka, B. F. Stucky, G. D. 1998. Generalized syntheses of large-pore mesoporous metal oxides with semicrystalline frameworks. Nature 396 152-155. 

The importance of framework density and molar volume is evident also for large pore, mesoporous silica [33] and for AIPO4 polymorphs [34], Data for the latter are included in Figure 7.19. For mesoporous silica a transition from a regime where cages and pores affects the energetics to one in which the large pores act as inert diluent is reported. A further increase in pore diameter does not appear to increase the enthalpy of the compound [33], The similarity in enthalpy of many different structures shows that the synthesis of metastable microporous framework... 

The greater activity of Ti-beta (vs. TS-1) in the oxidation of the bulky cyclohexane was noted in the previous section. Table IX provides a comparison of the conversion and epoxide selectivity in the reaction catalyzed by TS-1 and three large-pore/mesoporous Ti-silicates in the epoxidation of a single, linear allyl alcohol (pentenol). 

DEALUMINATIQN OF ZEOLITE Y Dealumination is an important process to improve the thermal stability and resistance to acid of zeolite. This is one of the main techniques for preparing zeolite catalysts (US-Y). New pores (mesopores) have been introduced during hydrothermal treatment (Fig.4), which were directly confirmed by electron microscopy. The density of mesopores depended on the degree of dealumination and the size distribution of mesopores... 

Whole pore Mesopore Micropore Mesopore Increment... 

Poly(oxyethylene) oleyl ethers as templating agents for the synthesis of large pore mesoporous materials... 

The bulkier 1,3,5 TIPB showed about one order of magnitude faster diffusion in Si-MCM-41 than in NaX zeolite (16). Moreover, contrary to prevalent expectation, this molecule shows higher diffusivity than the smaller xylene isomers. These observations are indicative of the diffusion occurring in larger cylindrical pores (mesopores) of the Si-MCM-41 sample. However, diffusivity values of 1,3,5 TIPB, as well as PFTBA, are of the 10 9 cm2/s order, which is more typical of diffusion in zeolites and other microporous materials. The relatively slow diffusion of these molecules in the larger mesopores could be related to some hindrance effects resulting from structural defects and/or from the presence of extra-framework materials in the cylindrical mesopores. 

Figure 1.2,Si NMR spectra of functionalized mesoporous silica, (a) Large pore mesoporous silica (50 A) with low degree of hydration and low coverage (25%). (b) Large pore mesoporous (50 A) with a higher degree of hydration and a higher coverage, (c) Small pore mesoporous silica (20 A).

Synthesis Pore Width BET SSA Total Pore Mesopore Micropore ... 

FABRICATION OF THREE-DIMENSIONAL LARGE-PORE MESOPOROUS CHANNELS BASED ON ORDERED MESOPOROUS SILICA MATERIALS... 

The synthesis of molecular sieves with large pores is of great importance for many applications such as catalysis, separation, adsorption and fabrication of various quantum materials [1-7]. With the recent discovery of hexagonal and cubic large pore mesoporous materials (SBA-15, SBA-16, FDU-1) [2,3], block copolymers have turned out to be valuable supramolecular templates for the synthesis of ordered large pore mesoporous materials because of their facile structure-directing ability, low-cost commercial availability and biodegradability. 

In this paper, we demonstrate a novel method to generate 3D large-pore mesoporous channels, which involved the introduction of organic co-solvents followed by a high... 

The pores carbon phase indicate hydrophobic properties, responsible for the affinity for particles of organic compounds. Due to low specific surface of macropores (0.5 - 2 mVg), their adsorption capacity is considered negligible. However they play the role of the transportation routes, enabling the difiusion of adsorbed substances to narrower pores. The similar function can be attributed to intermediate pores - mesopores with the specific surface in the range of 10 - 400 m /g. 

In the case of the smallest pores (mesopores and micropores), the developed area is very large and the permeability is very low. Thus the thickness of the separative layer must be thin enough to reach attractive fluxes with experimentally acceptable transmembrane pressure. On the other hand, the mechanical strength of the membrane must be large enough to withstand the applied pressure. These considerations led to the concept of asymmetric structure based on macroporous support and successive layers with decreasing thickness and pore size (Table 25.3 Figure 25.1). 

When the catalyst is immobilized within the pores of an inert membrane (Figure 25.13b), the catalytic and separation functions are engineered in a very compact fashion. In classical reactors, the reaction conversion is often limited by the diffusion of reactants into the pores of the catalyst or catalyst carrier pellets. If the catalyst is inside the pores of the membrane, the combination of the open pore path and transmembrane pressure provides easier access for the reactants to the catalyst. Two contactor configurations—forced-flow mode or opposing reactant mode—can be used with these catalytic membranes, which do not necessarily need to be permselective. It is estimated that a membrane catalyst could be 10 times more active than in the form of pellets, provided that the membrane thickness and porous texture, as well as the quantity and location of the catalyst in the membrane, are adapted to the kinetics of the reaction. For biphasic applications (gas/catalyst), the porous texture of the membrane must favor gas-wall (catalyst) interactions to ensure a maximum contact of the reactant with the catalyst surface. In the case of catalytic consecutive-parallel reaction systems, such as the selective oxidation of hydrocarbons, the gas-gas molecular interactions must be limited because they are nonselective and lead to a total oxidation of reactants and products. For these reasons, small-pore mesoporous or microporous... 

In summary, one can see that separation selectivity for gas and vapor molecules depends on the category of pores (mesopores, supermicropores, and ultramicropores) and on the related transport mechanisms. Either size effect or preferential adsorption effect (irrespective of molecular dimension) is involved in selective separation of multicomponent mixtures. The membrane separation selectivity for two gases is usually expressed either as the ratio between the two pure gas permeation fluxes (ideal selectivity) or between each gas permeation flux measured from the mixture of the two gases (real selectivity). More detailed information on gas and vapor transport in porous ceramic membranes can be found in Ref. [24]. 

Use of mixture of surfactant (e.g., C18-3-1 and CTAB for MCM-41, Gemini surfactant mixture for MCM-48) as template and post-synthesis hydrothermal treatment.[1] This method can give high-quality and large-pore mesoporous silica materials. 

Block copolymers are valuable supramolecular templates for the synthesis of ordered large-pore mesoporous silica and other metal oxides because of their simple templating ability, low-cost commercial availability, and biodegradability. 

P.D. Yang, D.Y. Zhao, D.I. Margolese, B.F. Chmelka, and G.D. Stucky, Generalized Syntheses of Large-pore Mesoporous Metal Oxides with Semicrystalline Frameworks, Nature (London), 1998, 396, 152-155. 

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