Transformation process of boehmite to γ-Al₂O₃ induced by high-energy ball milling

In its nanoparticulate form, active alumina (gamma-Al2O3) exhibits promising potential as a catalyst support material for diverse applications. We report a simple synthesis of nano-crystalline grain gamma-Al2O3 by the mechanochemical dehydration of boehmite (gamma-AlOOH) at room temperature. The results showed that well-crystalline gamma-Al2O3 could be obtained by high-energy milling for more than 32 h via amorphous boehmite. The BET specific surface area (S-BET) decreased from 228.10 m(2) g(-1) to 136.15 m(2) g(-1), accompanied by a significant decrease in the pore volume (V-t) from 0.264 cm(3) g(-1) to 0.16 cm(3) g(-1). Interestingly, the relative percentage of AlO6 decreased to 85.78%, and the number fraction of AlO4 reached a value of approximately 14.22% in this process. But, the AlO5 disappeared completely with the increase in milling time. The amorphous boehmite was generated through dehydration and dehydroxylation of boehmite precursors during the ball milling process, accompanied by the appearance of high content of the AlO5. Several structural rearrangements from boehmite precursors to gamma-Al2O3 could be governed by the interconversion between the AlO6, AlO5 and AlO4. Revealing the intricate formation mechanism of gamma-Al2O3 through high-energy ball milling facilitates the target-oriented design of alumina materials.