CO2 Hydrogenation on Carbides Formed in situ on Carbon‐Supported Iron‐Based Catalysts in High‐Density Supercritical Medium

CO₂ conversion via hydrogenation over iron‐based catalysts on non‐carbon supports produces mainly CO or methane by the Sabatier reaction, while the formation of C₂₊ hydrocarbons is of greatest interest. C_xH_y production from CO₂ may be considered as a two‐step process with the initial formation of carbon monoxide by the reverse water gas shift reaction followed by the Fischer‐Tropsch synthesis (FTS). In the present work CO₂ hydrogenation over iron‐based catalysts (Fe, FeCr, FeK) deposited on a carbon carrier has been studied. The catalyst structure has been investigated by XRD, TEM, XPS, Mössbauer spectroscopy and in situ magnetometry. Spinel‐type oxide phases (magnetite Fe₃O₄; maggemite γ‐Fe₂O_3, and, in the case of FeCr/C catalyst, iron chromite Fe_1+xCr_2‐xO₄) are formed on the catalysts, and they contribute exclusively to the CO production. Iron carbides, active in FTS, are formed on Fe‐ and FeK‐catalysts during pre‐activation in reducing environment and then during the reaction. The reaction over the 20Fe1K/C catalyst in supercritical high‐density CO₂/H₂ substrate (400 °C, 8.5 MPa) leads to 72 % selectivity for C₁–C₁₂₊ hydrocarbons (alkanes and alkenes). Under the same conditions, iron carbides do not form on the FeCr/C catalysts, and CO₂ hydrogenation results in the CO formation with the selectivity of 90–100 %.