In situ probes into the structural changes and active state evolution of a highly selective iron-based CO2 reduction photocatalyst

Harnessing solar energy for CO2 conversion to fuels presents a sustainable alternative to fossil fuels. However, finding an economical, stable, non-toxic nanomaterial catalyst poses a significant challenge. Understanding the catalyst's active state is vital for optimal performance due to potential structural changes during reactions. Herein, we employ various in situ characterizations to detail δ-FeOOH's structural evolution during hydrogen activation, identifying its active phase while catalyzing the heterogeneous reduction of CO2 by H2. Using in situ environmental transmission electron microscopy, δ-FeOOH is first dehydrated to α-Fe2O3, then reduced to Fe3O4, and finally to α-Fe. Other in situ characterizations revealed that the active state of the catalyst (Fe-350-H2) is a mixture of Fe3O4 and α-Fe. A detailed investigation into the photocatalytic CO2 reduction using batch, flow, and LED reactors unveiled that the Fe-350-H2 catalyst exhibits superior activity and selectivity in activating the reverse water gas shift reaction compared with similar iron-based catalysts.