Effect of La addition on thermal microstructural evolution of macroporous alumina monolith prepared from ionic precursors

Abstract

Porous alumina monoliths with high thermal stability have been prepared using sol-gel processing from ionic precursors. Samples were synthesized from AlCl3·6H2O and LaCl3·7H2O dissolved in a H2O/etanol solution containing poly(ethylene oxide) (PEO) via propylene oxide (PO) involved sol-gel reaction accompanied by phase separation. The heat-treated gels consist of controllable size of macropores and La-doped alumina skeletons. Doped lanthanum ions are homogeneously embedded in the gel matrix, which retards the phase transition from γ-alumina to α-alumina during the sintering. The 3 mol% La-doped aluminate exhibits the BET surface area of 55.3 m2/g, after the heat treatment at 1100°C for 24 h. Drying condition are also related to the thermal stability of obtained gels. Aluminate aerogels show higher thermal stability than corresponding xerogels due to relatively large mesopore size and high porosity. As a result, the 3 mol% lanthanum doped aluminate aerogel shows BET surface area as high as 82.5 m2/g even after heat treatment at 1100°C for 24 h.