Reticulated Alumina Replica Foams with Additional Sub‐Micrometer Strut Porosity

Ceramic alumina foams are suitable catalyst supports with high temperature stability used, for example, in catalytic cracking processes or combined heat and power units. Herein, such replica foams are generated from macroporous α‐Al₂O₃ powder synthesized by a sol–gel process. The foam windows, constituting intrinsic (macroscopic) foam porosity, are supplemented by an additional porosity within the struts of the foams. These pores, originating from the sol–gel process, are preserved during sintering at 1350 °C. This results in less dense foams compared with foams from conventional alumina powders. Foams sintered at 1350 °C exhibit an increased strut porosity of ≈62%, of which ≈84% are open, with pore diameters in the range of 200–500 nm and a compressive strength of 0.2 MPa. Foams sintered at 1600 °C or higher possess an almost tenfold compressive strength but no additional strut porosity. Due to the use of carboxylic acids as porogenes in the sol–gel process, all samples generated from sol–gel‐derived alumina powder exhibit significantly higher porosity values than the respective reference foams made from commercial alumina powder. Although specific surface areas of ≈3 m² g⁻¹ are still small, this value is significantly improved by additional strut porosity.