Surface Area and Porosity Changes in Iron Catalysts During Activation and Initial Use in the Fischer-Tropsch Synthesis

Abstract

The impact on iron Fischer-Tropsch catalysts of the variables controlling the initial precipitation, subsequent aging and drying conditions has been detailed. Heat treatment of iron oxyhydroxides causes the surface area to decrease and the major pore size to increase as the temperature increases, both in air and in an inert atmosphere. A shift toward higher temperature stability is seen for the same iron oxyhydroxide when co-precipitated with 6% Al 2 O 3 , SiO 2 , or ZrO 2 . Samples for characterization are withdrawn from the reactor at increasing time intervals during pretreatment and exposure to synthesis gas. Surface area decrease and pore size increase are also observed during pretreatment with CO at 260°C and 100 psi. and during the initial days of reaction under CO/H 2 . The major changes appear to occur during pretreatment and in the very early stages of the reaction. The effects of added promoter (s) also impact the area and/or porosity of the materials. The area and pore size distributions have shown systematic changes during increasing exposure to synthesis gas.