Synthesis and characterization of aerogel-derived cation-substituted barium hexaaluminates Original Research Article

New methods have been demonstrated for the synthesis of high surface area cation-substituted hexaaluminates. These materials hold promise for use as catalysts in high temperature combustors. The hexaaluminates were prepared by calcining high surface area aerogels at temperatures up to 1600°C. In comparing unsubstituted and cation-substituted hexaaluminates, we found that phase transformations for the cation-substituted materials were more direct. Small amounts of BaCO3 and BaAl2O4 were observed during transformation of the unsubstituted materials, while the cation-substituted materials transformed directly from an amorphous phase to crystalline hexaaluminate. The presence of substitution cations also caused the transformation to occur at lower temperatures. Manganese appears to be a better substitution cation than cobalt since BaMnAl11O19−α exhibited higher surface areas and methane combustion reaction rates than BaCoAl11O19−α. A doubly substituted material, BaMn0.5Co0.5Al11O19−α, was more active than its singly substituted counterparts. This result suggests a synergy between Mn and Co in the barium hexaaluminates.