Design of bifunctional single-atom catalysts NiSA/ZIF-300 for CO₂ conversion by ligand regulation strategy

Carbon-supported noble-metal-free single-atom catalysts (SACs) have aroused widespread interest due to their green chemistry aspects and excellent performances. Herein, we propose a “ligand regulation strategy” and achieve the successful fabrication of bifunctional SAC/MOF (MOF = metal–organic framework) nanocomposite (abbreviated NiSA/ZIF-300; ZIF = ZIF-8) with exceptional catalytic performance and robustness. The designed NiSA/ZIF-300 has a planar interfacial structure with the Ni atom, involving one S and three N atoms bonded to Ni(II), fabricated by controllable pyrolysis of volatile Ni-S fragments. For CO₂ cycloaddition to styrene epoxide, NiSA/ZIF-300 exhibits ultrahigh activity (turnover number (TON) = 1.18 × 10⁵; turnover frequency (TOF) = 9830 mol_SC·mol_Ni⁻¹·h⁻¹; SC = styrene carbonate) and durability at 70 °C under 1 atm CO₂ pressure, which is much superior to Ni complex/ZIF, NiNP/ZIF-300, and most reported catalysts. This study offers a simple method of bifunctional SAC/MOF nanocomposite fabrication and usage, and provides guidance for the precise design of additional original SACs with unique catalytic properties.