Photoexcited Single-Electron Transfer for Efficient Green Synthesis of Cyclic Carbonate from CO2

It is attractive but challenging to produce high-value-added cyclic carbonates at ambient condition by the 100% atom-economic photocatalytic cycloaddition of CO2, which is limited by the insufficient understanding of the catalytic mechanism. Here, by taking Mg-MOF-74 as a model system, we propose the photoexcited catalyst can generally activate CO2 via single-electron-transfer mechanism, leading to the rapid formation of ()CO2- radical. Subsequently, beneficial for the activation of inert CO2, the energy barrier of the rate-determining step (RDS) of the whole cycloaddition, i.e., the CO2 attacking step, significantly decreases, resulting in the feasible synthesis of cyclic carbonates under ambient condition. With the combination of synchrotron radiation in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), in situ electron spin resonance (ESR) spectroscopy, and the density functional theory calculation, the reaction process and corresponding key intermediates are systematically investigated, revealing the CO2 activation to be the most energy consumption steps in cyclic carbonate production, rather than the ring-opening of epoxide, thus furnishing new insights into photocatalytic CO2 cycloaddition.

Automated summary

By studying the Mg-MOF-74 model system, we found that the photoexcited catalyst can activate CO2 through a single-electron-transfer mechanism, forming ()CO2- radical, thereby reducing the energy barrier of the cycloaddition reaction and enabling the synthesis of cyclic carbonates at ambient temperature.