Aerogel powders consisting of small, highly porous, high surface area particles, which offer an easy accessibility to reaction sites, are excellent candidates as catalyst. These catalysts are mostly produced by supercritical drying from organic solvents or liquid carbon dioxide, but aerogel-like powders can also be prepared from aqueous gels by freeze-drying which is safer and permits the use of inexpensive precursors. The preparation method based on freeze-drying and the characteristics of resulting alumina and chromia powders are described. These powders, cryogels, are characterized by properties very similar to those of aerogels: bulk densities <200 kg/m(3), specific surface areas >250 m(2)/g, large interparticle macropore volumes (>5 cm(3)/g). These properties are the consequence of a fractal, nearly two-dimensional morphology of individual particles.