Pretreatment effect studies with a precipitated iron Fischer-Tropsch catalyst

Abstract

A doubly promoted precipitated iron catalyst (100 Fe/0.3 Cu/0.8 K by mass) was characterized after different pretreatment conditions and after Fischer-Tropsch (FT) synthesis in a fixed bed reactor. The BET surface area of the catalyst decreased markedly after pretreatments with hydrogen, carbon monoxide and synthesis gas ( H CO 0.67 and 2). Calcined catalyst was in the form of α-Fe 2O 3, which was converted to either metallic iron (α-Fe) or a mixture of α-Fe and Fe 3O 4 after hydrogen reductions. During FT synthesis the α-Fe was carburized to iron carbides (χ-carbide or ϵ′-carbide) or oxidized to Fe 3O 4. After carbon monoxide or syngas pretreatments, the χ-carbide was the most dominant phase. During FT synthesis this carbide was partially or completely converted to ϵ′-carbide, Fe 3O 4, and/or FeCO 3. Hydrogen reductions resulted in stable or increasing catalyst activity with time on stream and the reduction conditions had a strong effect on the subsequent catalyst activity. The carbon monoxide and syngas pretreated catalysts deactivated with time. The hydrogen reduced catalysts produced more methane and gaseous hydrocarbons than the carbon monoxide or the syngas pretreated catalysts, and favored secondary hydrogenation and isomerization reactions.