Special Issue "Aerogel Catalyst"
Deadline for manuscript submissions: closed (30 September 2012).
Interests: membrane reactors; carbon membranes; carbon dioxide capture; hydrogen
Special Issues and Collections in MDPI journals
The term aerogel describes a material obtained by supercritical extraction of the liquid of a gel, itself consisting of a solid three-dimensional network that ensnares a liquid medium. Drying by transition from the liquid to the supercritical phase does away with the capillary forces, which act in evaporation and cause partial or total collapse of the pore network. Hence, supercritical drying leads to materials with low density, high specific surface area, large pore volume and very versatile pore size. The first aerogels were produced from silica gels in 1937. Since then, the sol-gel technique has expanded to other inorganic materials such as alumina or titanium oxide, for instance, then to carbon in the late 1980s.
Extending the original definition, literature includes in aerogel-like materials a large variety of nanostructured porous solids. One can cite, for instance, materials obtained by supercritical drying of precipitates, which maintain a loose structure with non-agglomerated primary particles. Cryogels synthesized by freeze-drying of gels, or xerogels, i.e. materials prepared via subcritical drying but that nevertheless maintain a substantial fraction of the original gel pore texture, constitute an interesting alternative to the (costly) supercritical drying.
The inherent properties of aerogels and aerogel-like supports render them very attractive in catalytic applications, as shown by the constantly renewed interest of research groups for this technology through the years. Besides high dispersion of the active phase, made possible by high surface areas, the high pore volume and tunable pore size of aerogels lead to the possibility of designing catalyst supports that facilitate the diffusion of reactants and products to and from the active sites. The indubitable improvements in catalytic performance obtained through use of aerogel supports should of course outweigh their higher processing cost. To this end, the development of efficient manufacture processes is crucial and should constitute the last step towards large-scale use of catalysts supported on these fascinating engineered supports.
Dr. Theophilos Ioannides
Dr. Nathalie Job
- catalyst supports
- nanostructured materials