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.