Self-functionalization of cellular alumina monoliths in hydrothermal conditions

Abstract

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 alpha-Al2O3 ceramics by micro/nano structures of boehmite (gamma-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. (C) 2015 Elsevier Ltd. All rights reserved.