Reactivity of surface carbonaceous intermediates on an iron-based Fischer–Tropsch catalyst

Abstract

The reactivities of surface carbonaceous intermediates on both a freshly reduced and a carbided iron-based Fischer–Tropsch catalyst were characterised using isotopic transient kinetic analysis (SSITKA), isothermal hydrogenation, and temperature programmed surface reactions. On both catalysts, carbon deposition occurred to the same extent but water formation and methane formation were faster on the carbided catalyst. More reaction intermediates for C 2 hydrocarbon formation were detected at the start of the Fischer–Tropsch reaction on the freshly reduced catalyst. However, the CH s intermediate for methane formation and the CCH s intermediate for C 2 hydrocarbon formation were found to be the most stable surface intermediates on both catalysts. Surface carbon ( 13C s), deposited via the Boudouard reaction using 13CO, was active and was detected in the C 2+ hydrocarbon products as the result of a coupling reaction with 12C s rather than with 13C s. Six distinct carbon pools (C α1, C α2, C β1, C γ1, C γ2, and C δ1) were identified during isothermal and temperature programmed surface reactions. Graphitic carbon (C δ1) has the highest coverage of all the surface carbonaceous species on the end of the run sample.