Ammonium aluminium carbonate hydroxide NH4Al(OH)2CO3 as an alternative route for alumina preparation: Comparison with the classical boehmite precursor

Abstract

Ammonium aluminium carbonate hydroxide (AACH) is a promising alternative precursor for preparation of alumina with high purity and original textural properties. In this paper, both boehmite (classical alumina precursor) and AACH were precipitated in a stirred tank reactor with close process parameters. Preparation protocols were thus compared. Main differences between both protocols were pointed out (reactant molar ratio influence, alumina concentration, filtration/washing step). This study helps for the choice of the appropriate preparation route for alumina precursor synthesis. As-synthesized boehmite and AACH precursors were then calcined between 500°C and 1000°C. The textural properties of the corresponding aluminas were characterized. At 500°C, AACH-derived alumina revealed to be particularly porous, with larger mean pore diameter (ca. 29nm) than boehmite-derived alumina (ca. 6nm). Moreover, AACH-derived alumina exhibited a high surface area. However, a more accurate analysis revealed that this high specific surface area (407m2·g−1) is mostly due to microporosity formation during the calcination step. At higher calcination temperature, boehmite and AACH-derived aluminas exhibited different behaviors against sintering. In particular, the latter showed an interesting ability to maintain a constant mean pore diameter, regardless of the calcination temperature.