Visible-Light-Driven Conversion of CO2 to CH4 with an Organic Sensitizer and an Iron Porphyrin Catalyst

摘要： Using a phenoxazine-based organic photosensitizer and an iron porphyrin molecular catalyst, we demonstrated photochemical reduction of CO2 to CO and CH4 with turnover numbers (TONs) of 149 and 29, respectively, under visible light irradiation (λ > 435 nm) with a tertiary amine as sacrificial electron donor. This work is the first example of a molecular system using an earth-abundant metal catalyst and an organic dye to effect complete 8e-/8H+ reduction of CO2 to CH4, as opposed to typical 2e-/2H+ products of CO or formic acid. The catalytic system continuously produced methane even after prolonged irradiation up to four days. Using CO as the feedstock, the same reactive system was able to produce CH4 with 85% selectivity, 80 TON and a quantum yield of 0.47%. The redox properties of the organic photosensitizer and acidity of the proton source were shown to play a key role in driving the 8e-/8H+ processes.