In Situ Raman Spectroscopic Studies on Iron‐Based Catalysts During CO2 Fischer–Tropsch Synthesis

Abstract

AbstractKnowledge about dynamic changes of the phase composition during catalytic reactions is indispensable for gaining a better understanding of catalyst structure‐reactivity relationships. For this purpose, in situ Raman spectroscopic experiments were conducted to monitor the structural changes of ferrous oxalate without and with an alkali metal promoter during CO2 hydrogenation to C2+‐hydrocarbons under realistic reaction conditions (340 °C, 15 bar). The kind of promoter had no significant influence on the thermal transition of iron oxalate into the magnetite (Fe3O4) phase as the major phase under inert gas. In contrast, the promoters did have a substantial impact on the phase composition during CO2 hydrogenation. The Raman spectroscopic results obtained, underpinned with X‐ray diffraction measurements, demonstrated a much stronger development of carbon‐containing species, notably iron carbides (FeCx) and carbon deposits, when using the alkali metal‐promoted catalysts. The formation of carbon deposits may indirectly indicate the occurrence of carbidization, however, no quantitative correlation was discovered. It was also found that the presence of alkali metal promoters hampered the reoxidation of FeCx toward Fe3O4 with water vapor.