CO₂ Hydrogenation on Carbides Formed in situ on Carbon-Supported Iron-Based Catalysts in High-Density Supercritical...

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 %.