Synergistic Surface and Bulk Engineering Enables Optimal χ-Fe5C2/Fe3O4 Interfaces on FeAlK Catalysts for Efficient CO2 Hydrogenation to Heavy Olefins

Abstract Catalytic hydrogenation of CO2 with renewable H2 to heavy olefins (C5+=), which are traditionally produced from petroleum resources, offers a promising route for carbon-neutral and long-chain hydrocarbons production. However, achieving efficient conversion of CO2 to heavy olefins over Fe-based catalysts remains a great challenge, primarily due to the difficulty in controlling the dynamic structural evolution of catalysts during the reaction. Herein, K and Al co-promoted FeAlKx catalysts were fabricated, and in situ formed χ-Fe5C2/Fe3O4 interfaces were subsequently constructed for CO2 hydrogenation to heavy olefins. A high C5+= space-time yield of 453.7 mg·gcat−1·h−1 was achieved over the FeAlK8 catalyst under the reaction conditions of 330 °C, 2.0 MPa, and 20,000 mL·gcat−1·h−1. The dynamic structural evolution of the FeAlKx catalysts was elucidated by in situ X-ray diffraction, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe Mössbauer spectroscopy characterizations. Operando diffuse reflectance infrared Fourier transform spectroscopy, H2/D2 isotope exchange, and C3H6 and CO pulse probing hydrogenation experiments also helped to reveal the reaction mechanism and the structure−performance relationship of the catalysts. The optimal χ-Fe5C2/Fe3O4 interfaces and abundant bulk χ-Fe5C2 species are responsible for highly efficient CO2 hydrogenation to heavy olefins. In addition, the FeAlK8 catalyst presented a high thermal stability during an 800 h long-term test, demonstrating a promising industrial application for CO2 hydrogenation to heavy olefins. This study also provides a facile strategy for developing Fe-based catalysts with dynamical structural evolution toward efficient CO2 hydrogenation.