Synthesis of hierarchically structured aluminas under controlled hydrodynamic conditions

Aluminas having hierarchical bimodal pore structures with regular arrayed macropores interconnected with mesopores were synthesized in a cone/plate apparatus that provided well-defined hydrodynamic conditions. A parametric synthesis study was performed to better understand the synthesis conditions required to form the hierarchical structures. The synthesis experiments demonstrated that the hierarchnical structure could only be formed under limited mixing conditions. The mesoporous structure, which was created by interstitial porosity between boehmite nanoparticles, was formed independently of the macropores and was not significantly impacted by the use of a surfactant, whereas the formation of the macropores required the presence of an alkoxide droplet within the synthesis mixture and the surfactant played no role other than to influence the hydrodynamic conditions during synthesis.