Dynamics of Reaction‐Induced Changes of Model‐Type Iron Oxide Phases in the CO2‐Fischer‐Tropsch‐Synthesis
Aleks, Arinchtein; Meng‐Yang, Ye; Qingxin, Yang; Carsten, Kreyenschulte; Andreas, Wagner; Marvin, Frisch; Angelika, Brückner; Evgenii, Kondratenko; Ralph, Kraehnert
Iron-based catalysts are employed in CO2-FTS due to their ability to convert CO2 into CO in a first step and their selectivity towards higher hydrocarbons in a second CO hydrogenation step. According to the literature, iron carbides represent the active phase for hydrocarbon formation and are claimed to emerge in the presence of CO. We propose nanostructured FeOx films as model systems to assess information about the complex phase transformations during CO2-FTS. Mesoporous hematite, ferrihydrite, maghemite, maghemite/magnetite films were exposed to CO2-FTS atmospheres at 20 bar and 300 °C. Up to three distinct phases were observed depending on the time-on-stream (TOS): a sintered maghemite/magnetite phase, a carbidic core-shell structure, and a low-crystalline, needle-type oxide phase. Our findings indicate that the formation of an intermediary maghemite/magnetite phase, predominant after short TOS (30 h), precedes the evolution of the carbide phase. Yet, even after prolonged TOS (185 h), no full conversion into a bulk carbide is observed.
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