The influence of phosphate and sulphate ions on the surface texture of alumina

The impact of the addition of phosphate and sulphate salts to aluminas, viz. gamma-alumina and dried alumina gel, on their surface textures is described. This has been achieved through an analysis of nitrogen adsorption data for structurally characterised test samples. Modification through impregnation by phosphate and sulphate salts did not result in detectable bulk changes, the structure remaining very similar to that of gamma-alumina in all cases. However, as far as the texture was concerned, the addition of both phosphate and sulphate salts resulted in a ca. 15% reduction in the S-BET value for gamma-alumina due to changes in the porosity. Modified alumina gel exhibited a higher surface area than either pure or modified gamma-alumina. Thus, for the purposes of obtaining catalytically important acidified aluminas with higher surface areas, it is recommended that phosphates or sulphates be added to the parent alumina gel prior to calcination.