Metallic oxides are widely used as catalysts because of their high surface area and low particle size. The most common method of synthesis to obtain such materials is the sol-gel technique. We describe the synthesis of nanoscaled high surface area aluminum and alumina materials of various shapes by adsorption of a precursor solution on various substrates, followed by controlled calcinations.
The adsorption of a 0.3 mol L-1 aluminum hydride solution in diethyl ether on fibrous carbonaceous substrate (cellulose fibers, carbon fibers or felts), followed by a calcination (Ar, 250C) led to the thermolysis of the hydride and the formation of metallic particles (~ 300 nm, s.a. : 30 - 90 m2 g-1) on the surface of the fibers. Aluminum microtubes composed of similar sizes particles and of equivalent surface areas were obtained by oxidation of the substrate at 600C. By heating treatments at higher temperatures, both γ and α alumina phases respectively crystallized. Microtubes are formed of agglomerated particles, the surface area of the α phase obtained at 1600C is about 40 m2 g-1.
Lamellar aluminas (s.a. ~ 80 to 250 m2 g-1) of extremely low apparent density (15 g dm-3) were synthesized by immersion of exfoliated or exfoliated-recompressed graphite (Papyex) in 1 mol L-1 aluminum trichloride solutions in diethylether. In a first step, after a partial calcination (exfoliated graphite) or a pseudo-exfoliation (Papyex), a carbon / aluminum oxichloride composite was obtained. Its subsequent calcination (O2, 1200C) led to the crystallization of α - alumina sheets with nanometric thicknesses (ca. 10 nm). After dispersion in water, these latter were divided into nanometric pulverulent fragments by the mechanical effect of ultra sounds.
Similar methods were used for the synthesis of other metallic particles (Co, Ag) and oxides (Co3O4, TiO2, HfO2, CeO2...) that are reported as catalytic materials.