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

Abstract

In its nanoparticulate form, active alumina (γ-Al₂O₃) exhibits promising potential as a catalyst support material for diverse applications. We report a simple synthesis of nano-crystalline grain γ-Al₂O₃ by the mechanochemical dehydration of boehmite (γ-AlOOH) at room temperature. The results showed that well-crystalline γ-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 m² g⁻¹ to 136.15 m² g⁻¹, accompanied by a significant decrease in the pore volume (V_t) from 0.264 cm³ g⁻¹ to 0.16 cm³ 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 γ-Al₂O₃ could be governed by the interconversion between the AlO₆, AlO₅ and AlO₄. Revealing the intricate formation mechanism of γ-Al₂O₃ through high-energy ball milling facilitates the target-oriented design of alumina materials.