The effect of altering CO2-conversion on iron-based direct CO2-hydrogenation

Abstract

Direct CO₂-hydrogenation to liquid hydrocarbons is seen as a valuable reaction pathway for using hard-to-mitigate CO₂ emissions to synthesize drop-in sustainable fuels. CO₂-hydrogenation is a complex reaction with much dispute over the reaction mechanism, viz., whether a dual or only a single active site is needed. The conversion-selectivity relationship within direct CO₂-hydrogenation in a slurry phase reactor over an iron-based catalyst is reported on and the prevalence of a single catalytically active site is shown. The effect of conversion on the reaction selectivity can be utilised to maximise the yield of the desired C₂₊ hydrocarbons. Rate-based insights are provided, most notably the strong inhibition of the reaction rate by water formed in-situ, which may be used to further understand and improve the reaction performance. Finally, it is shown that operating a fixed bed reactor outperforms the performance in a slurry phase in terms of catalyst bed activity more than expected based on the flow profile.