Mesoporous sieves

Since the first synthesis of siliceous mesoporous molecular sieves described in the literature in 1992 [1], several mesoporous materials possessing various T atoms together with Si in the lattice have been prepared. The synthesis and properties of niobium- and siliceous-containing mesoporous sieves of MCM-41 type were first time described by our group [2,3] and almost parallely, Nb-doped mesoporous sieves were synthesized by Zhang and Ying [4]. 

As example, Figure 4 displays H2-TPR profiles of A1MCM-41 mesoporous sieves modified in various ways with nickel [12]. Two samples were impregnated by Ni(NC>3)2 (profiles a and... 

Nb-containing mesoporous sieves are hydrothermally and mechanically more stable than A1MCM-41. 

B. J. Melde, B. T. Holland, C. F. Blanford, and A. Stein, Mesoporous sieves with unified hybrid inorganic/organic frameworks, Chem. Mater. 11, 3302-3308 (1999). 

Another limitation in the industrial application of peroxidases is the low stability to H202 (see Chap. 12). Here, an improvement for H202 inactivation through the physical immobilization of CPO on the mesoporous sieve SBA-15 of 130 A for the oxidation of indole to 2-oxoindole has been reported [8]. The performance of the immobilized enzyme was enhanced to that of the native CPO with respect to maximum conversion. According to the authors, the superior performance of... 

According to the data from calorimetric investigations of the adsorption of ammonia, unlike silica gel, the pure-silica mesoporous sieve MCM-41 possesses specific although weak acidity. The introduction of titanium or zirconium, and parhcularly aluminum, ions into the structure of this sieve substantially increases the acid strength of the sorbent [120, 121]. 

This material was able to act as a solid Bronslcd base catalyst and accelerated the Knoevenagel condensation of ethyl cyanoacetate with benzaldehyde better than basic forms of mesoporous sieves and zeolite catalysts. It was found that this carboxylate-functionafized LLC material exhibited enhanced basicity due to the ordered nanostructure, and that the LLC pores were capable of substrate molecular size exclusion [114],... 

Recently, mesoporous sieve-materials such as MCM-41 and FSM-16 have been synthesized by using different micelle surfactant templates such as alkyltrimethyl ammonium salts. - " These materials consist of ordered mesoporous channels of 20 100 A diameter, which are much larger than those in the conventional zeolites such as ZSM-5, AlPO-5, and NaY, as depicted in Fig. 2. They are potential hosts for the inclusion of organometallic complexes and nanoparticles that will align with the ordered channels of the mesoporous materials and are accessible to larger substrates in the catalytic reactions. 

Compared to layered clay, the mesoporous sieves (e.g., SBA-15, MCM-41) have large pore volume for loading guest molecular [99-101]. Introducing PANI into mesopores of mesoporous sieves have also attracted a significant attention [99]. The schematic diagram of a PANI/MCM-41 particle is... 

What is very promising is the possibility to synthesize t irge-pore titanium-containing molecular sieves. The crux of the synthesis of these mesoporous sieves is to avoid the hydrolysis of the titanium component (such as tetrabutyl orthotitanate) to large titania particles. The performed syntheses of mesoporous titanosilicates have proved that the hydrolysis of TBOT to larger titania particles can be prevented. 

Neutral route - various amines, triblock copolymers, and alkyl-ethylene oxides are used for preparation of different hexagonal mesoporous sieves, SBA-15, SBA-16, or OMAs. 

In the J. Heyrovsk Institute we performed a detailed study of (a) M0O3 supported on siliceous mesoporous sieves of several types and (b) rhenium (VII) oxide supported on organized mesoporous aluminas in order to (i) verify positive effect of these supports on catalyst activity, (ii) to find out the most convenient way for catalyst preparation, (iii) to receive detailed information about their catalytic activity and selectivity, and (iv) to show the applicability of these catalysts in different types of metathesis reaction. 

Properties of M0O3 supported on siliceous mesoporous sieves... 

Molybdenum and rhenium oxide eatalysts based on siliceous mesoporous sieves and OMA, respectively, proved enhanced catalytic activity in comparison witii corresponding catal) using conventional supports. The origin of tiiis enhanced activity is not completely clear and is still a subject of discussions and continuous research. The better accessibility of catalysts site located in mesopores undoubtedly represents tire essential contribution to the increased catalytic activity. Rhenium (VII) oxide on organized mesoporous alumina preserves known tolerance of Re catalysts to the polar-substituted olefins. The presence of cocatalysts like Mc4Sn is essential similarly as for conventional systems. However, tire catalysts with higher pore size were found to deliver better results. 

Lanthanum as additives was used for the modification of zeolite to improve their catalytic performance. In addition, lanthanum-containing microporous and mesoporous molecular sieves are synthesized using for many kinds of catalytic reactions. That is to say, the addition of lanthanum into molecular sieves contains the two types one is lanthanum used as skeleton atom the other is as non-skeleton atom. But for the applications of molecular sieves as catalytic materials in heterogeneous catalysis, it s generally accepted that the molecular sieves are divided into the microporous and mesoporous sieves. Herein, we adopt the latter method of dividing the lanthanum modified molecular sieves into lanthanum modified microporous and mesoporous molecular sieves. 

While most solid-polymer mixed-matrix membranes rely on sieve micropores to generate high selectivities within the membrane by discriminating between gas penetrants, mesoporous molecular sieves have been studied as well. These mesoporous sieves arc used to increase permeabUity in mixed-matrix membranes, instead of enhancing selectivity. Mesoporous MCM-41 incorporated into a polysulfone matrix improved membrane permeability for aU gases tested. The selectivity of pure polysulfone was maintained, as expected. Mesoporous sieves are an excellent material for highly selective polymer membranes that require increased productivity however, nanoscopic-scale crystals will probably be required to enable accommodation within the submicron selective layer typical for high-performance asymmetric membranes in use today. 

Feng C, Li Y, Liu X (2012) Photocatalytic degradation of imidacloptid by phosphotungstic acid supported on a mesoporous sieve MCM-41. Chin J Chem 30 127-132... 

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