Abstract:
High-surface area (25 m(2) g(-1)) Mn-doped barium hexa-aluminates with compositions BaMnAl11O19 and BaMn2Al10O19 were prepared by a combination of hydrothermal precipitation-calcination route. The precursors of the above two compounds were obtained by hydrolyzing a mixture of aqueous solutions of Ba, Al, and Mn at 180 degreesC for 1 h in the presence of urea. The analysis of the hydrothermally prepared samples showed the presence of carbonate and/or hydroxide phases of Ba and Mn and boebmite. Barium mono-aluminate (BaAl2O4), Ba-beta(II)-Al2O3, gamma-Al2O3, and a small fraction of MnO2 were observed after calcination of these hydrothermally prepared precursors at 1200degreesC. A mixture of Ba-beta(1)-Al2O3 and Ba-beta(II)-Al2O3 phases were found after calcination at 1400degreesC for 2 h with no other oxide phases of Ba, Al or Mn. (C) 2003 Elsevier B.V. All rights reserved.