Self-functionalization of cellular alumina monoliths in hydrothermal conditions

Alumina-based open cellular microstructures with highly interconnected porosity attract much interest as supports for catalytic applications, with emphasis on petroleum and automotive sector. This work reports a novel route for in-situ functionalization of the sintered porous α-Al2O3 ceramics by micro/nano structures of boehmite (γ-AlOOH), promoted by hydrothermal treatment in alkaline conditions. The mechanism of the process includes slow dissolution of the matrix, which acts as an aluminum precursor, and transport of Al-containing species inside the pores, resulting in growth of boehmite fibers and clusters of various morphologies, as confirmed by combined SEM/EDS/XRD/FTIR. These results suggest that deliberate variation of the pH and ionic strength of the hydrothermal medium may represent a promising strategy for controlling the spatial distribution, morphology and dimension scale of the grown boehmite. A complementary approach implies pre-treatment of cellular monoliths in highly-reducing conditions to increase the concentration of surface defects and dangling bonds, facilitating the matrix dissolution and probably acting as nucleation centers, and thus to boost the functionalization level.