Hydrogenation of CO2 to Valuable C2-C5 Hydrocarbons on Mn-Promoted High-Surface-Area Iron Catalysts

Abstract

Mn-promoted bulk iron catalysts with a high specific surface area (82–211 m2·g−1) were synthesized by coprecipitation followed by drying under supercritical conditions. The catalysts were tested in the CO2 hydrogenation to valuable C2-C5 hydrocarbons. The Mn-promoted iron catalysts exhibited better textural properties than the bare Fe2O3 catalyst, allowing better dispersion of the active phase, easier reduction and carburization of iron oxides and, consequently, resulting in higher catalytic activity than the bare Fe2O3 catalyst. The best activity results were obtained by catalyst promotion with a very low amount of Mn (Mn/Fe atomic ratio of 0.05). Upon steady state conditions (T = 340 °C, total pressure of 20 bar and H2/CO2 = 3), this catalyst exhibited high CO2 conversion (44.2%) and selectivity to C2-C4 hydrocarbons (68%, olefin to paraffin ratio of 0.54), while the selectivity to C5+ hydrocarbons, CH4 and CO was about 3.2, 38.5 and 5%, respectively. A close correlation was found between catalyst textural properties and CO2 conversion. The most active MnFe-0.05 catalyst exhibited high stability during 72 h of reaction related to a low amount of soft coke formation and catalyst activation through the formation of the χ-Fe5C2 phase during the on-stream reaction.