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

Abstract

A photochemical reduction of CO2 to CO and CH4 was shown using the iron porphyrin catalyst Fe(pTMAPP)Cl5 in combination with the phenoxazine photosensitizers 5,10-Di(2-naphthyl)-5,10-dihydrophenazine and 3,7-Di((1,1'-biphenyl)-4-yl)-10-(naphthalen-1-yl)-10H-phenoxazine. Turnover numbers (TONs) up to 149 for CO and 29 for CH4 were reached. The experiments were conducted under visible-light irradiation (λ > 435 nm) with a tertiary amine (see section SEDs below) as sacrificial electron donor.

Advances and special progress

The first demonstration for the reduction of CO2 to CH4 (complete 8e–/8H+ reduction) by a combination of an earth-abundant metal catalyst and an organic dye. So far, similar systems were shown to induce 2e–/2H+ reduction of CO2 to CO or formic acid.

Additional remarks

Methane was produced continuously (even after irradiation up to 4 days). The 8e–/8H+ reduction efficiency strongly depends on the redox properties of the organic photosensitizer and acidity of the proton source.

In additional experiments, CO was used as the gas resource. The system consisting of iron porphyrin catalyst Fe(pTMAPP)Cl5 in combination with the phenoxazine photosensitizer 5,10-Di(2-naphthyl)-5,10-dihydrophenazine and 3,7-Di((1,1'-biphenyl)-4-yl)-10-(naphthalen-1-yl)-10H-phenoxazine was able to produce CH4 with a TON of 80 (85% selectivity, quantum yield: 0.47%).

Catalysts

Fe(pTMAPP)Cl5

Photosensitizers

5,10-Di(2-naphthyl)-5,10-dihydrophenazine 3,7-Di((1,1'-biphenyl)-4-yl)-10-(naphthalen-1-yl)-10H-phenoxazine

Investigations

1. REDIRECT Photocatalytic reduction of CO2

Investigation-Name: Table 1Export

The article contains additional information on CO-reduction with the same system as additional information. The system gives higher conversion rates to CH4 and is not added here yet.

Sacrificial Electron Donor

In this study, the experiments were done with the sacrificial electron donors DIPEA (DIPEA), TEOA (TEOA), BIH (BIH), and TEA (TEA).

Additives

In this study, different additives were used. As depicted in the investigation table, water (H2O,) phenol (PhOH), and trifluoroethanol (TFE) were used.