Aerogels skeletal

Table 13.3 summarizes the polymeric systems that have been applied to silica. In effect, the underlying inorganic framework plays the role of a structure-directing agent (template). The mechanical property improvement is attributed to reinforcement of the interparticle necks, which are the weak points of the aerogel skeletal framework. In turn, the stabilization provided by the crosslinking polymer is attributed to the extra chemical bonds created by the interparticle polymeric tethers. 

To date, metal-doped carbon aerogels and xerogels have been used as catalysts in different reaction types, which can be grouped into environmental and fuel cell applications, C=C double-bond hydrogenation, skeletal isomerization, hydrodechlorination, and other reactions, including synthesis of methyl... 

In the case of catalysts supported on carbon, Moreno-Castilla et al. [42] prepared a WO3/C aerogel by the one-step method. That catalyst was used in the skeletal isomerization of 1-butene for which it exhibited a good selectivity in isobutene, an easy diffusion of reactants and products, as well as a low deactivation with reaction time thanks to an adequate pore structure. 

C. Moreno-CastUla, F. J. Maldonado-H6dar, J. Rivera-UtriUa, and E. Rodriguez-Castellon, Group 6 Metal Oxide-Carbon Aerogels. Their Synthesis, Characterization and Catalytic Activity in the Skeletal Isomerization of 1-Butene, Appl. Catal. A, 183, pp. 345-56, 1999. 

Silica aerogels are amorphous materials. They have a skeletal density, as measured by Helium pycnometry [102] 2 g cm, close to that of amorphous silica (2.2 g cm ). They typically have a pore volume above 90% of their whole monolith volume. Some ultraporous... 

Ayral A, Phalippou A, Woignier T (1992) Skeletal density of silica aerogels determined by helium pycno-metry. J Materials Science 27 1166-1170... 

Flguro 13.2. Scanning electron micrographs iSEM) at random spots in the interior of a riactuied native silica aerogel monolith (A., pb = 0.169 gem ) and after the skeletal network was coated (crosslinked) widi Desmodur N3200-derived polyurea (B., Pb = 0.380 g cm ). 

Figure 13.20. A. Poly[acrylonitrile]-crossliiiked silica decorated with Si-AIBN (pt = 0.47 gcm", 60%, w/w, polymer, 228 g 60%, v/v, empty space). B. Pure silicon carbide aerogel by pyrolysis of the poly[acrylonitrile]-crosslinked silica shown in A. (pi, = 0.97 gcm, skeletal density Ps = 3.12 gcm , 39 g" , 69%, v/v, empty...

Sisk C N, Hope-Weeks J (2008) Copper(II) aerogels via 1,2-epoxide gelation. J Mater Chem 18 2607-2610 Leventis N, Vassilaras P, Fabrizio E F, Dass A (2007) Polymer nanoencapsulated rare earth aerogels chemically complex but stoichiometrically similar core-shell superstructures with skeletal properties of pure... 

RF-MOx wet gels have been dried either in an autoclave with SCF CO2 to yield native RF-MOx aerogels or under ambient pressure and temperature to produce RF-MOx xerogels. Alternatively, the RF-MOx skeletal framework was coated conformally (crosslinked) with a polyurea (PUA) derived by polymerization of a triisocyanate (Desmodur N3300A from Bayer) in an analogous fashion to what has been described for the RF and the MOx networks... 

Single sample, average of 50 measurements in brackets calculated skeletal densities based on the thermogravimetric analysis data of the next column and the skeletal densities of native MOx, RF and polyurea (PUA) aerogels prepared independently (see text). 

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