Ambient-Pressure CO2 Hydrogenation to Olefins over Ag-Tailored CoFe2O4 Catalyst Powered by Natural Sunlight

Abstract

Direct hydrogenation of carbon dioxide (CO2) to light olefins using renewable H2 offers a promising route to complement petroleum-based olefin production. Atmospheric-pressure operation is particularly attractive because it reduces the compression requirements associated with high-pressure CO2 hydrogenation. However, coupling the reverse water-gas shift (RWGS) reaction with Fischer–Tropsch synthesis (FTS) remains challenging under atmospheric pressure. Here, we report an Ag-modified cobalt-iron oxide catalyst (Ag/CoFe) that enables CO2 hydrogenation to light olefins (C2=–C4=) at atmospheric pressure. Mechanistic investigations indicate that Ag incorporation enhances the availability of RWGS-derived CO, which facilitates Fe carburization and Fe5C2 formation. The resulting Fe5C2 phase promotes C–C coupling and chain propagation, thereby shifting the hydrocarbon product distribution from methane toward light olefins. At 320 °C and 0.1 MPa, the optimized Ag/CoFe catalyst achieves 34.4% CO2 conversion, with C2=–C4= and CH4 accounting for 64.4 and 31.2%, respectively, of the hydrocarbon products. Under photothermal operation driven by natural sunlight, the catalyst delivers 31.6% CO2 conversion, with C2=–C4= accounting for 62.7% of the hydrocarbon products, without external electrical heating. These results demonstrate atmospheric-pressure solar photothermal CO2 hydrogenation to light olefins and identify the coupling of RWGS-derived CO supply with Fe carburization as an effective strategy for promoting RWGS–FTS tandem catalysis under atmospheric pressure.