Gamma Alumina Spherical Nanopowder by Homogeneous Precipitation

The gamma alumina is frecuently used as a catalyst and catalytic supports due to its great specific surface area, chemical activity and low cost. g-alumina is generally derived from pseudoboehmite because it tranforms to gamma alumina at low temperatures without decreasing its specific surface area.

In this work homogeneous precipitatión was used to prepare amorphous spherical basic aluminum sulfate and this was tranform into aluminum hydroxide by topotactic neutralization with hydroxide ammonium solution. This hydroxide was dried by spray drying (SD), freeze drying (FD) and normal drying (ND) to obtain PB. Finally, PB was calcined to transform it to g-alumina. On the other hand, effects of starch and chitosan on g-alumina´s texture were studied adding these polymers during homogeneous precipitation.

A weight loss with a broad endothermic peak below 450 °C corresponding to OH elimination was observed by the thermal analysis of PB. The PB calcined at 450 °C for 3 hours is g-alumina according to powder XRD. The morphology of g-alumina was an agglomerate with spherical nano particles (f=30 nm) by SEM. This nanoparticles was indeed conformed with nonofibers (f=2 nm, l=10 nm) after observed by TEM.

Texture of SD derived g-alumina was: S_BET=384 m²/g; f_pore=76.8 Å; and V_pore=0.73 cm³/g.  g-alumina prepared by FD and ND had a slightly lower S_BET (350 and 332 m²/g, respectively). On the other hand, the starch increased the f_pore up to 151 Å and V_pore to1.02 cm³/g, in contrast the chitosan decreased the f_pore to 80 Å and V_pore to 0.66 cm³/g.