Fischer-Tropsch synthesis: activity and selectivity of chi-Fe5C2 and circle minus-Fe3C carbides

Abstract

Two different iron carbides, Hägg (χ-Fe5C2) and cementite (ϴ-Fe3C) for Fischer-Tropsch synthesis (FTS) was investigated. Both iron carbides were oxidized to Fe3O4 ​during FTS. Hägg carbide (χ-Fe5C2), initially exhibits higher FT and WGS activity compared to cementite (ϴ-Fe3C) under similar reaction conditions. However, Hägg carbide deactivates much faster rate than cementite and their FT activity was levels-off after a certain period on FTS. Under similar level of CO conversion, Hägg carbide exhibits slightly higher methane selectivity compared to cementite. The ratio of FT to WGS selectivity for Hägg carbide increases with increasing time-on-stream and it remains more or less the same over cementite. The observed FT and WGS activity correlate to the % carbide content of iron on used FT catalyst which indicates that carbide is the active form of Fe for both FT and WGS reaction.