Tandem Photocatalysis of CO₂ to C₂H₄ via a Synergistic Rhenium-(I) Bipyridine/Copper-Porphyrinic Triazine Framework

Abstract

The photocatalytic conversion of CO₂ into C₂₊ products such as ethylene is a promising path toward the carbon neutral goal but remains a big challenge due to the high activation barrier for CO₂ and similar reduction potentials of many possible multi-electron-transfer products. Herein, an effective tandem photocatalysis strategy has been developed to support conversion of CO₂ to ethylene by construction of the synergistic dual sites in rhenium-(I) bipyridine <i>fac</i>-[Re^I(bpy)(CO)₃Cl] (Re-bpy) and copper-porphyrinic triazine framework [PTF(Cu)]. With these two catalysts, a large amount of ethylene can be produced at a rate of 73.2 μmol g^-1 h^-1 under visible light irradiation. However, ethylene cannot be obtained from CO₂ by use of either component of the Re-bpy or PTF(Cu) catalysts alone; with a single catalyst, only monocarbon product CO is produced under similar conditions. In the tandem photocatalytic system, the CO generated at the Re-bpy sites is adsorbed by the nearby Cu single sites in PTF(Cu), and this is followed by a synergistic C-C coupling process which ultimately produces ethylene. Density functional theory calculations demonstrate that the coupling process between PTF(Cu)-*CO and Re-bpy-*CO to form the key intermediate Re-bpy-*CO-*CO-PTF(Cu) is vital to the C₂H₄ production. This work provides a new pathway for the design of efficient photocatalysts for photoconversion of CO₂ to C₂ products via a tandem process driven by visible light under mild conditions.