Formation of Lanthanoid-β-alumina and Its Thermal Properties

Abstract

The preparation and properties of, a support material consisting of lanthanoid oxides and alumina have been studied for use as combustion catalysts at high temperatures. Mixtures of lanthanoid oxides and alumina were prepared by means of coprecipitation method. The specific surface area of the support with La content of 5 mol% was 37 m²/g when calcined at 1200°C for 2 h (Fig.1), and the only product identified by X-ray diffraction analysis was lanthanum β-alumina (La₂O₃.11-14 Al₂O₃) (Fig.4). Addition of Pr or Nd into Al₂O₃ gave rise to the formation of β-Al₂O₃-type compounds having specific surface area of about 20 m²/g (Fig.10). La, Pr, or Nd addition retarded the transformation of γ-Al₂O₃ to α-Al₂O₃ and associated sintering. However, addition of Y, Sm, Gd or Dy mainly gave perovskite type compounds, having specific surface area of less than 10 m²/g.
β-Al₂O₃-type compounds showed high surface area and were resistant to the thermal sintering above 1000°C.