In the present review, aerogels designate dried gels with a very high relative pore volume. These are versatile materials that are synthesized in a first step by low-temperature traditional sol-gel chemistry. However, while in the final step most wet gels are often dried by evaporation to produce so-called xerogels, aerogels are dried by other techniques, essentially supercritical drying. As a result, the dry samples keep the very unusual porous texture which they had in the wet stage. In general these dry solids have very low apparent densities, large specific surface areas, and in most cases they exhibit amorphous structures when examined by X-ray diffraction (XRD) methods. In addition, they are metastable from the point of view of their thermodynamic properties. Consequently, they often undertake a structural evolution by chemical transformation, when aged in a liquid medium and/or heat treated. As aerogels combine the properties of being highly divided solids with their metastable character, they can develop very attractive physical and chemical properties not achievable by other means of low temperature soft chemical synthesis. In other words, they form a new class of solids showing sophisticated potentialities for a range of applications. These applications as well as chemical and physical aspects of these materials were regularly detailed and discussed in a series of symposia on aerogels,1-5 the last of them being held in Albuquerque in 2000.6 Reviews were also regularly published, either on both xerogels and aerogels7 or more focused on the applications of aerogels.8-13 The particularly interesting properties of aerogels arise from the extraordinary flexibility of the solgel processing, coupled with original drying techniques. The wet chemistry is not basically different for making xerogels and aerogels. As this common basis has been extensively detailed in recent books,14 it does not need to be reviewed. Compared to traditional xerogels, the originality of aerogels comes from * To whom all correspondence should be addressed. † Institut de Recherches sur la Catalyse. ‡ Laboratoire d’Application de la Chimie à l’Environnement. 4243 Chem. Rev. 2002, 102, 4243−4265

https://is.muni.cz/el/1431/podzim2006/C7780/um/Read/2711172/aerogel_Pajonk_ChRev02_4243.pdf

Chemistry of Aerogels and Their Applications

Aerogels, which are nanoscale mesoporous materials of low density
and high surface area, have been well studied as thermal insulators, heterogeneous
catalysts, and novel particle or radiation detectors. Now, electrically conducting
oxide aerogels are being explored as new materials in electrochemistry and
for their innate ability to amplify the nature of the surfaces of technologically
relevant conducting oxides in batteries, ultracapacitors, and fuel cells.
Recent results are reviewed in which the mixed electron- and cation-conducting
transition metal oxides of vanadium, molybdenum, ruthenium, and manganese
have been prepared as low density, highly porous, and high surface area aerogels
and then studied as charge-storage electrode materials. These materials challenge
the standard ways in which electrochemically active oxides are conceived,
studied, and used.

Electrically conductive oxide aerogels: newmaterials in electrochemistry

The oxidative upgrading of amines offers great opportunities for the sustainable production of key N-containing building-blocks for the modern chemical industry. Compared to other oxyfunctionalizations, and despite their potential, amine oxidation reactions are barely explored in the literature. This review aims at drawing attention to this important area and highlights both the major achievements and the challenges that still remain.

Developments in the Aerobic Oxidation of Amines

Introduction Aerogels offer interesting opportunities for catalysis due to their unique morphological and chemical properties. These properties originate from their wet-chemical preparation by the solution-sol-gel (SSG) method and their subsequent liberation from the solvent via critical-point drying or supercritical (or hypercritical) drying (SCD). Due to the “structure-preserving” ability of SCD, the usually oxidic (or metallic) aerogels are solids of high porosity and specific surface area.

P.M. Zambri

Papers

Aerogels as hydrogenation catalysts

The selective oxidation of cyclohexylamine to its oxime