Influence of a partial dissolution of alumina during the preparation of iron catalysts on their catalytic properties for Fischer-Tropsch synthesis

Abstract

Three iron-alumina catalysts were prepared by different methods: ammonia precipitation, impregnation and mechanical mixture. Their reactivity was studied under pressure in the carbon monoxide hydrogenation reaction. Important differences were observed both in activity and selectivity. Their characterization was made by magnetization measurements and by CO adsorption-thermodesorption. The results were interpreted in terms of a partial dissolution of alumina when it is put in contact with an acid solution and the subsequent reprecipitation to form a superficial solid solution with Fe 3+. These Fe 3+ ions would be more difficult to reduce and would lead to less active sites in the H 2 + CO reaction. This hypothesis was verified on a series of iron catalysts precipitated on different aluminas. An inverse relation was found between the Fischer-Tropsch activity and the concentration of soluble alumina.