Encapsulation of Single Iron Sites in a Metal-Porphyrin Framework for High-Performance Photocatalytic CO2 Reduction.

Efficient CO2 reduction with earth-abundant photocatalysts is a highly attractive but very challenging process for chemists. Herein, we synthesized an indium-porphyrin framework, In(H2TCPP)(1-n)[Fe(TCPP)(H2O)](1-n)[DEA](1-n) (In-FenTCPP-MOF; H2TCPP = tetrakis(4-benzoic acid)porphyrine; DEA = diethylamine), with a porphyrin ring supporting the single-site iron for the high-performance visible-light-driven conversion of CO2 to CO. A high CO yield of 3469 μmol g-1 can be achieved by a 24 h photocatalytic reaction with a high CO selectivity (ca. 99.5%). This activity was much higher than that of its cobalt analogues or the Fe-free indium-based metal-organic framework (MOF). Systematic experimental and theoretical studies indicate that the porphyrin-supported iron centers in the MOF matrix serve as efficient active sites, which can accept electrons from the photoexcited MOFs in order to mediate CO2 reduction.