Deciphering the structural evolution and real active ingredients of iron oxides in photocatalytic CO2 hydrogenation

Photocatalytic CO₂ hydrogenation reactions can produce high-value-added chemicals for industry, solving the environmental problems caused by excessive CO₂ emissions. Iron oxides are commonly used in photocatalytic reactions due to their various structures and suitable band gaps. Nevertheless, the structural evolution and real active components during photocatalytic CO₂ hydrogenation reaction are rarely studied. Herein, a variety of iron oxides including α-Fe₂O₃, γ-Fe₂O₃, Fe₃O₄ and FeO were derived from Prussian blue precursors to investigate the CO₂ hydrogenation performance, structural evolution and active components. Especially, the typical α- and γ-Fe₂O₃ are converted to Fe₃O₄ during the reaction, while Fe/Fe_xO_y remains structurally stable. Meanwhile, it is confirmed that Fe₃O₄ is the main active component for CO production and the formation of hydrocarbons (CH₄ and C₂–C₄) are highly dependent on the Fe/Fe_xO_y heterojunctions. The optimal yields of CO, CH₄ and C₂–C₄ hydrocarbons over the best catalyst (FeFe-550) can achieve 4 mmol g⁻¹ h⁻¹, 350 μmol g⁻¹ h⁻¹ and 150 μmol g⁻¹ h⁻¹, respectively due to their suitable metal/oxide component distribution. This work examines the structural evolution of different iron oxide catalysts in the photocatalytic CO₂ hydrogenation reaction, identifies the active components as well as reveals the relationship between components and the products, and offers valuable insights into the efficient utilization of CO₂.