Synthesis and Processing of Barium Hexaaluminogallates

Barium hexaaluminogallate was synthesized by the mixed-oxide method and the coprecipitation method. Barium hexaaluminate and barium hexagallate were found to form barium hexaaluminogallate, Ba(Al,Ga)₁₂O₁₉, at 1400°C. BaCo(Al,Ga)₁₁O₁₉ of magnetoplumbite structure was formed from a mixture of metal oxides at 1200°C for 6 h. Co was successfully introduced to barium hexaaluminogallate, although the synthesis of BaCoAl₁₁O₁₉ is quite difficult via solid-state reaction of oxide powders. Anisotropic BaCo(Al,Ga)₁₁O₁₉ particles crystallized at 1100°C for 2 h through the coprecipitation method using metal nitrates and ammonium carbonate. BaCo(Al,Ga)₁₁O₁₉ supported on a cordierite honeycomb had the ability to reduce NO _x with methane over 500°C in the presence of excess oxygen.