PRETREATMENT EFFECT STUDIES WITH A PRECIPITATED IRON FISCHER-TROPSCH CATALYST

A doubly promoted precipitated iron catalyst (100 Fe/0.3 Cu/0.8 K by m ass) was characterized after different pretreatment conditions and aft er Fischer-Tropsch (FT) synthesis in a fixed bed reactor. The BET surf ace area of the catalyst decreased markedly after pretreatments with h ydrogen, carbon monoxide and synthesis gas (H-2/CO 0.67 and 2). Calcin ed catalyst was in the form of alpha-Fe2O3, which was converted to eit her metallic iron (alpha-Fe) or a mixture of alpha-Fe and Fe3O4 after hydrogen reductions. During FT synthesis the alpha-Fe was carburized t o iron carbides (chi-carbide or epsilon'-carbide) or oxidized to Fe3O4 . After carbon monoxide or syngas pretreatments, the chi-carbide was t he most dominant phase. During FT synthesis this carbide was partially or completely converted to epsilon'-carbide, Fe3O4, and/or FeCO3. Hyd rogen reductions resulted in stable or increasing catalyst activity wi th time on stream and the reduction conditions had a strong effect on the subsequent catalyst activity. The carbon monoxide and syngas pretr eated catalysts deactivated with time. The hydrogen reduced catalysts produced more methane and gaseous hydrocarbons than the carbon monoxid e or the syngas pretreated catalysts, and favored secondary hydrogenat ion and isomerization reactions.