Ultralow loading atomically dispersed Fe on N-doped carbon hollow shells for efficient CO₂ cycloaddition

Developing highly efficient single-atom catalysts (SACs) with optimal active-site utilization remains challenging. In this study, a hollow macroporous-mesoporous catalyst composed of iron single atoms supported on nitrogen-doped carbon (Fe/NC) was synthesized using silica microspheres as a sacrificial template and dopamine hydrochloride as a bifunctional C/N source and iron-anchoring ligand, and applied to the CO₂ cycloaddition reaction. According to the experimental results, the Fe/NC catalyst demonstrates exceptional performance in the cycloaddition reaction of styrene oxide with CO₂, achieving a high yield of 97.45 ± 0.33% (turnover frequency (TOF) = 38.19 h^-1), despite having an extremely low iron loading of only 1.36 ± 0.01 wt%. This is attributed not only to the superior intrinsic catalytic activity of the FeN₄ active sites but also to the hollow mesoporous structure with a high specific surface area, which provides stable metal anchoring sites to effectively suppress iron atom aggregation, promotes continuous release of substrates and CO₂, enhances product diffusion, and thereby improves catalytic efficiency. In addition, the Fe/NC catalyst demonstrates excellent cycling stability, maintaining a high conversion efficiency of 93.26 ± 0.52% after five consecutive recycling tests while preserving its structural integrity. Moreover, the Fe/NC catalyst exhibits broad substrate compatibility. This work provides a theoretical basis for synthesizing porous C/N materials with single-atom loading to achieve efficient catalytic conversion of carbon dioxide.