Alumina ceramic foams as catalyst supports

Ceramic foams have a wide range of potential applications in biomedicine, thermal insulation, filtration of molten metal alloys, adsorption of environmental pollutants, catalyst supports, etc. Since the physical properties of the foams do not fully meet the requirements in some applications, improvement of conventional fabrication methods or totally new techniques are of interest. Herein, three main methods of manufacturing ceramic foams are introduced with the main emphasize on the replica technique. Furthermore, different techniques for improving structural properties of ceramic foams are reviewed. The focus of this review is on fabrication of macro-porous alumina foams with high interconnected porosity. In addition, experimental data for manufacturing of ceramic foams via the replica technique are presented along with literature surveys. Slurries consisted of alumina powder mixed in aqueous solutions of polyvinyl alcohol (PVA) and magnesia and titania as sintering aids. The foams were produced by tuning different processing parameters to give properties suited for catalyst supports. These parameters included pore size of the polyurethane (PU) foam used as a template, parameters in the PU foam pretreatment, particle size of alumina powder in the slurry, slurry loading and drying of the green alumina coated PU foam. Finally, the key factors for optimizing ceramic foams in terms of mechanical strength and interconnectivity are introduced together with an outlook for future advances in ceramic foams as catalyst supports.