Carbon Pathways, Sodium-Sulphur Promotion and Identification of Iron Carbides in Iron-based Fischer-Tropsch Synthesis

Abstract

Fisher-Tropsch Synthesis (FTS) is industrially used for converting a carbon-containing feedstock, such as coal, natural gas, biomass, and municipal waste, via the production of synthesis gas (a mixture of CO+H2) into hydrocarbons. This review article focuses on Fe-based FTS catalysis, thereby focusing on the process conditions available for steering the various carbon pathways from input CO and their associated reactions. We will also discuss the effects of alkali-sulphur chemical promotion and the identification of the FTS reaction active Fe carbides, which are assigned with precise crystal structures and nomenclature. Each observed Fe carbide crystal structure is further assigned with corresponding Mössbauer Absorption Spectroscopy (MAS) hyperfine fields. The expected formation temperatures and experimental conditions for the identified Fe carbides encountered in FTS research, namely ϵ-Fe3C, η-Fe2C, χ-Fe5C2, θ-Fe3C and θ-Fe7C3, are reviewed.