Revealing the Effects of χ-Fe ₅ C ₂ Species on CO ₂ Hydrogenation to Olefins

The conversion of CO 2 to olefins using iron-based catalysts has garnered significant interest due to its potential in reducing CO 2 emissions. Herein, a Na-promoted ZnFe 2 O 4 catalyst exhibits a high CO 2 conversion (36.0%) and olefin selectivity (81.0%). Based on the combined results of various characterization techniques, including XPS, Mössbauer spectroscopy, XAS, and DFT calculations, the ZnFe 2 O 4 catalyst induces a relatively electron-deficient state in the χ-Fe 5 C 2 species compared with Zn-promoted iron oxide catalyst, thereby promoting olefin formation during CO 2 hydrogenation. DFT calculations show that the ZnFe 2 O 4 catalyst demonstrates a favorable capability for CH 2 coupling to form olefins. The Na promoter enhances CO 2 adsorption, thereby reducing the H/C ratio on the catalyst surface and promoting the formation of olefins. The synergistic effect between the Na promoter and the relatively electron-deficient χ-Fe 5 C 2 species on the 0.5Na/ZnFe 2 O 4 catalyst results in the highest observed olefin selectivity during CO 2 hydrogenation.