SURFACE-AREA STABILITY AND CHARACTERIZATION OF A NOVEL SULFATE-BASED ALUMINA MODIFIED BY RARE-EARTH AND ALKALINE-EARTH IONS

The properties of a novel alumina prepared by decomposition of aluminium sulfate at 1000-degrees-C have been investigated. The surface area following heat treatment at 1200-degrees-C is more than a factor of two greater than that of conventional aluminas. Diffuse reflectance infrared spectroscopy measurements show that the types of hydroxyl groups present on the surface of the novel alumina differ from those of a conventional gamma-alumina. It appears that the surface of the former may be predominantly of a type which contains aluminium ions in octahedral sites alone. This may be a factor in the enhanced sintering resistance. Inclusion of some rare earth and alkaline earth oxides enhances sintering resistance in the usual way. The extent of improvement correlates with cation size, with La3+ and Ba2+ showing the greatest effect. Barium loadings of ca. 5 mol-% are required to maximise retained area but X-ray photoelectron spectroscopy measurements show that the near surface Ba/Al ratio does not exceed 0.02. X-ray diffraction patterns of highly loaded samples show the presence of two types of barium aluminate. A barium carbonate-like surface layer is formed on equilibration with air.