Tuning the hydrogenation of CO2 to lower olefins: Impact of Pt in K–doped Fe–Mn catalysts

Fe-based catalysts are promising for the hydrogenation of CO₂ to olefins, contributing to the mitigation of CO₂ emissions. Low-pressure conditions (∼1 MPa) are preferred for the selective synthesis of lower olefin because these conditions suppress carbon chain growth and olefin re-absorption which leads to hydrogenation of olefins to paraffins. In this study, K-doped Fe–Mn–Pt/Al₂O₃ catalysts that could react at 1 MPa were prepared, with a focus on the role and position of Pt active sites. K–Fe₁₇Mn₂/Pt₁/Al₂O₃ was prepared by first supporting Pt on Al₂O₃ followed by Fe–Mn oxide; it exhibited the highest C_2–5 olefin selectivity of 28 %. Pt promoted the reverse water-gas shift reaction, and in combination with Mn, facilitated iron oxide reduction and Fe₅C₂ formation, enhancing the C_2–5 olefin selectivity. Compared with the Pt active sites in K–Pt₁/Fe₁₇Mn₂/Al₂O₃, which was prepared by first supporting Fe–Mn oxide on Al₂O₃ followed by Pt, those in K–Fe₁₇Mn₂/Pt₁/Al₂O₃ existed around the Fe–Mn active sites. Pt continued to contribute to the Fe species reduction and the stable supply of CO, leading to improved C_2–5 olefin selectivity.