Macroporous alumina with three-dimensionally interconnected pore structure: Synthesis, characterization and transformation mechanism

Amorphous macroporous alumina with three-dimensionally interconnected pore structure was prepared by phase separation technique. The macroporous morphology was modified significantly by hydrothermal treatment with ammonia. There are many plate-like aggregates of alumina with a size of 50-300 nm at the edge of wall; the product is still characterized by the worm-like three-dimensional penetration and uniform spatial distribution, whereas the size of macropores decreases from 430 to 250 nm. The modified alumina material was converted into high crystallinity gamma alumina by calcination at 550℃, which displays a specific surface area of up to 331 m²/g and pore size distributions con-centrated at 8.9 and 250 nm; meanwhile, the Lewis acidity and crushing strength are also improved. It was speculated that the amorphous hydrated hydroxyaluminium ion polymer rehydrated to form boehmite intermediate and transformed into gamma state at low calcination temperature; the AlOOH particles at the edge of macropore wall were then rearranged from inside to outside with NH₄⁺ as template, fabricated into plate-like aggregates.