Iron silica aerogel

Some work has also been achieved with heterogeneous catalysis. These catalysts include Amberlyst-15, Nafion-H, montmorillonite KSF clay, ferrihydrite silica gel aerogels containing 11-13% iron, silica sulfuric acid, and zeolites. ... 

Since 1905, when Coblentz obtained the first IR spectrum, vibrational spectroscopy has become an important analytical research tool. This technique was then applied to the analysis of adsorbates on well-defined surfaces, subsequently moving towards heterogeneous reaction studies. Terenin and Kasparov (1940) made the first attempt to employ IR in adsorption studies using ammonia adsorbed on a silica aerogel containing dispersed iron. This led to a prediction by Eischens et al. from Beacon Laboratories in 1956 that the IR technique would prove to be extremely important in the study of adsorption and catalysis. For an excellent review article in IR spectroscopy, see Ryczkowski and references therein and for a more recent review with applications, see Topsoe. ... 

The Y value of the as-prepared aerogels was found to be 9.6 x 10 and 2.6 x 10 times smaller than those of Iron and Indium, respectively. The Y values of these aerogels are closer to those of rubber when compared with the metals mentioned above. It is only 2.6 X 10 times smaller than the Y value of rubber which is quite rarely observed in case of silica aerogels. This improvement in elastic modulus of superhydrophobic flexible aerogels with those of native silica aerogels is roughly two orders of magnitude. 

Figure 16.4. XRD patterns of iron oxide-silica aerogels obtained by soaking (Al) and by cogelation (B400) (reproduced from [10] by permission of Springer).

Casas LI, Roig A, Rodriguez E, MoUns E, Tejada J, Sort J (2001) Silica aerogel-iron oxide nanocomposites structural and magnetic properties. J Non-Cryst Solids 285 37-43... 

Casas LI, Roig A, Molins E, Greneche JM, Asenjo J, Tejada J (2002) Iron oxide nanoparticles hosted in silica aerogels. Appl Phys A 74 591-597... 

Finally, a very detailed EPR study of iron oxide-silica aerogels has been carried out by Fabrizioli et alP The CW X-band EPR spectra were very complex, and a multitude of signals were observed and assigned to isolated iron, tetrahedrally coordinated iron, iron oxide clusters and superparamagnetic iron oxide clusters. The g values ranged from 10 to 2.0, and all the spectra are thoroughly discussed, referenced and interpreted in this excellent paper." ... 

Iron oxide silica aerogel composites have been prepared by the sol-gel method followed by supercritical drying [6] and are found to be two or three orders of magnitude more reactive than the conventional iron oxide. The increase in reactivity was attributed to the large surface area of iron oxide nanoparticles supported on the silica aerogel. 

Magnetic silica aerogels generated from both pure ferric nitrate and its mixture with an iron complex exhibit low saturation magnetization values of 14 and 8.5 emu g , respectively [6], in comparison with bulk maghemite values of 74-76 emu g . The low magnetization values suggest lack of crystal order. These materials may still be useful in catalysis and other applications. 

Wang and Willey (260) report the oxidation of methanol in SCCO2 over pure and mixed oxide (Fe, Si, and Mo) aerogel catalysts. Selective oxidation products of dimethyl ether, methyl formate, and formaldehyde were found from 200°C to 300°C, and the selectivity depended on the catalyst used. Pure iron oxide favored dimethyl ether (80% yield), low levels of iron oxide on silica favored... 

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