Phase-Transformation of Gamma-Allumina to Alpha-Alumina as an Industrial Catalyst Support

Abstract

The phase transformation of aluminum hydrates yields various forms of alumina (d, q, K) and eventually alpha-alumina. The decrease in the specific surface area of alumina upon heat treatment is due to changes in crystalline structure and hence a decrease in the porosity of the material, Although the conversion of gamma-alumina to alpha-structure takes place with a lowering in surface area and pores, the use of such a material as a catalyst support yields high selectivity where the acidity is lowered and the surface area is maintained to some extent sufficiently low in catalyst preparation. The yield of alpha-alumina formation on the surface of starting material (gamma alumina) was investigated by the application of the final product in catalytic dehydration of methanol to dimethyl ether via kinetics measurements. The study of phase-transition kinetics and the influence of the effective factors leads to the possibility of selecting the desired process conditions for production of high selectivity alumina support. The activity, mechanical strength and stability of the catalyst supports are desired for application in certain chemical processes. While the low specific surface area alumina is produced, the porosity may be maintained high under firing conditions the favorable characteristics for appropriate industrial catalyst supports. The improvement of activity and selectivity of such supports is the main point of consideration.