Influence of surface area and additives on the thermal stability of transition alumina catalyst supports. I: Kinetic data

Abstract

The influence of surface area and additives on the transformation of transition aluminas into alpha alumina was studied using differential thermal analysis and by measuring the rate of transformation by X-ray diffraction of samples calcined at numerous intervals during a 50 hour period. Four transition alumina samples of different specific surface area ranging from 80 to 130 m 2 g −1 were used. The transformation was found to be facilitated by a high surface area of the initial transition alumina. Initially the surface area decreased very rapidly from its starting value until about 60 m 2 g −1 then more slowly and also linearly with respect to the amount of alpha phase in the sample. The influence of additives was followed by adding Mg 2+, Ca 2+, Ga 3+, In 3+, La 3+, Zr 4+ and Th 4+ cations by the dry impregnation method with nitrate salts. The influence of the method of preparation was determined by using the same procedure for aluminium nitrate. By comparison with pure alumina and in order of increasing effect. In 3+, Ga 3+, Al 3+ and Mg 2+ were found to be accelerators, whereas Zr 4+, Ca 2+, Th 4+ and La 3+ were found to be inhibitors. The influence of adding an ion to different initial aluminas was investigated in the case of Mg 2+.