Mesopore structure

CNFs, preparai by proper choice of foe synthesis conditions, were supported palladium and used for CTA hjfoogenation. Results indicated that Pd/CNF catalysts behave satisfectorily. The conversion of 4-CBA reached 98.3% with our novel Pd/CNF catalyst, while 90% with commercial Pd/C under similar evaluation conditions. This may attribute to foe unique mesoporous structure of CNF support r ucing foe diflusion resistance. 

The mechanical incorporation of active nanoparticles into the silica pore structure is very promising for the general synthesis of supported catalysts, although particles larger than the support s pore diameter cannot be incorporated into the mesopore structure. To overcome this limitation, pre-defined Pt particles were mixed with silica precursors, and the mesoporous silica structures were grown by a hydrothermal method. This process is referred to as nanoparticle encapsulation (NE) (Scheme 2) [16] because the resulting silica encapsulates metal nanoparticles inside the pore structure. 

Bhattacharya and Gedanken [11] have reported a template-free sonochemical route to synthesize hexagonal-shaped ZnO nanocrystals (6.3 1.2 nm) with a combined micro and mesoporous structure (Fig. 8.1) under Ar gas atmosphere. The higher porosity with Ar gas has been attributed to the higher average specific heat ratio of the Ar which leads to higher bubble collapse temperatures. With an intense bubble collapse temperature, more disorder is created in the product due to the incompleteness of the surface structure that led to greater porosity. Importance of gas atmosphere has been noted when the same process was carried out in the presence of air which results in the formation of ZnO without any porosity. 

Rana RK, Zhang L, Yu JC, Mastai Y, Gedanken A (2003) Mesoporous structures from supramolecular assembly of in situ generated ZnS nanoparticles. Langmuir 19(14) 5904—5911... 

As seen in the comparison of mesoporous silica and PMO in protein adsorption behavior, the nature of the framework of mesoporous materials has unavoidable influence on the protein adsorption. Therefore, adsorption of protein on mesoporous structures composed of hydrophobic materials such as carbon is worthy of detailed investigation. In this section, systematic research on protein adsorption on mesoporous carbon materials by Vinu and coworkers is mainly introduced. 

Encapsulation via the layer-by-layer assembly of multilayered polyelectrolyte (PE) or PE/nanoparticle nanocomposite thin shells of catalase in bimodal mesoporous silica spheres is also described by Wang and Caruso [198]. The use of a bimodal mesoporous structure allows faster immobilization rates and greater enzyme immobilization capacity (20-40 wt%) in comparison with a monomodal structure. The activity of the encapsulated catalase was retained (70 % after 25 successive batch reactions) and its stability enhanced. 

In this paper, the bulk material was obtained by impregnation of the silica host with GFP solution and nanosised by sonication, preserving the features of both the biomolecule and the mesoporous structure. An exhaustive physical chemical characterisation of the nanosized materials was performed by structural (X-Ray Diffraction, Transmission Electron Microscopy), volumetric and optical (photoluminescence spectroscopy) techniques. 

GFP/SBA-15 has shown a greater stability compared to pure GFP. The secondary structure of GFP/SBA-15 resists until 30 min of heating at 100°C, whereas that of pure GFP is wrecked after only 10 min of heating at 89°C. Then, the confinement inside a mesoporous structure strengthen also the physical properties of the protein. 

The aluminum is incorporated in a tetrahedral way into the mesoporous structure, given place to Bronsted acidic sites which are corroborated by FTIR using pyridine as probe molecule. The presence of aluminum reduces the quantity of amorphous carbon produced in the synthesis of carbon nanotubes which does not happen for mesoporous silica impregnated only with iron. It was observed a decrease in thermal stability of MWCNTs due to the presence of more metal particles which help to their earlier oxidation process. 

Figure 1 shows that the catalysts maintain their mesoporous structure with type IV isotherm. It can be observed a reduction in surface area, pore volume and pore diameter and slight increase in textural porosity as the concentration of aluminum increases (Table 1), due to the increase in the wall thickness in the mesoporous material as we have found previously [3],... 

In fact, after 5 reaction cycles the entrapped lipase shows a residual activity of the 60%, with respect to the total leaching that occurs after 3 or 2 reaction cycles for the adsorbed enzyme (Figure 2). Moreover, with respect to the biodiesel total productivity of the free lipase, the entrapped RML shows, after 5 reaction cycles, a value that is almost 6 times higher (1.62 mg FAME /mg Enz h and 0.28 mg FAME /mg Enz h, respectively for entrapped and free lipase). Concerning the stability of the inorganic matrix that covers the enzyme, after tested reaction cycles (five), mesoporous structure remains unaltered an stable (Figure 3). This indicates that the lipase leaching is due to the enzyme release and not to the collapse of matrix. 

Nickel containing MCM-36 zeolite was used as new catalyst in the ethylene oligomerization reaction performed in slurry semi-batch mode. This catalyst, with micro-mesoporous structure, mild acidity and well balanced Ni2+/acid sites ratio, showed good activity (46 g of oligomers/gcataLh) and selectivity (100% olefins with even number of carbon atoms). The NiMCM-36 behaviour was compared to those obtained with NiMCM-22, NiY, NiMCM-41 and NiMCM-48 catalysts. 

The development of composite micro/mesoporous materials opens new perspectives for the improvement of zeolytic catalysts. These materials combine the advantages of both zeolites and mesoporous molecular sieves, in particular, strong acidity, high thermal and hydrothermal stability and improved diffusivity of bulky molecules due to reduction of the intracrystalline diffusion path length, resulting from creation of secondary mesoporous structure. It can be expected that the creation of secondary mesoporous structure in zeolitic crystals, on the one hand, will result in the improvement of the effectiveness factor in hydroisomerization process and, on the other hand, will lead to the decrease of the residence time of products and minimization of secondary reactions, such as cracking. This will result in an increase of both the conversion and the selectivity to isomerization products. 

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