High specific surface area inherited from sea-urchin-like AACH clusters prepared by a novel spray precipitation

High specific surface of (α/γ)-Al 2 O 3 powder is essential for its applications in adsorbents, catalysts or ceramic raw materials. However, the phase transformation from precursor to oxide powder inevitably experiences the high-temperature calcination process which coarsens or agglomerates the particles, and then loses the high dispersity and activity. In this study, a novel spray precipitation operation was employed to synthesize the nanostructured ammonium aluminum carbonate hydroxide (AACH) and boehmite (γ-AlOOH) precursors in single precipitation method just depending on pH values. The high specific surface area (250.34 m 2 ·g −1 ) and high pore volume (0.96 ml·g −1 ) of as-prepared γ-Al 2 O 3 powder were inherited from fresh sea-urchin-like AACH precursor prepared at pH = 9. The sequential hydrolysis effect accelerated the unstable AACH precipitate to evolve into nearly spherical γ-AlOOH at a lower pH = 5. The special nano-clusters of AACH effectively reduced the phase transformation temperature of γ-Al 2 O 3 . In addition, the precipitation, nucleation and growth mechanisms and phase transformation sequences from different precursors to oxide powders were further proposed. Therefore, this work shows how pH value driving spray precipitation leads to a provisional change in morphology of precursors, but also to a permanent change in dispersion state of powders. It significantly affects the catalysis properties of Al 2 O 3 powders and its performance in adsorbent or electronic ceramics. These results are crucial for advancing Al 2 O 3 -supported technologies. Graphical abstract