Porphyrin-based metal-organic framework catalysts for photoreduction of CO2: understanding the effect of node connectivity and linker metalation on activity

Three zirconium-porphyrin based MOFs with different linker connectivity, PCN-222, PCN-223 and PCN-224, and their Zn(ii) ion metalated analogues, were prepared and used as catalysts for the photoreduction of CO(2)under visible-light irradiation. Before metalation with Zn(2+)in the porphyrin linkers, the lowest linker-connected PCN-224 (6-fold) exhibited a higher formate yield rate of 45.2 mu mol g(-1)h(-1)compared to PCN-222 and PCN-223. However, after the incorporation of Zn(2+)into the porphyrin, PCN-222-Zn showed the highest formate yield rate of 120.2 mu mol g(-1)h(-1). The density functional theory (DFT) computational results revealed that the catalytic activity correlated with the CO(2)adsorption affinity. The CO(2)adsorption energy on PCN-222-Zn (294.4 kJ mol(-1)) was the highest among all of the samples. The overall catalytic performance was affected by the Zr-6-oxo cluster connectivity and the introduced dual reaction sites when the porphyrin linkers were metalated with Zn(ii) ions.