Visible-Light-Driven Conversion of CO2 to CH4 with an Organic Sensitizer and an Iron Porphyrin Catalyst
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Abstract
Summary
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 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%).
Content of the published article in detail
The article contains results for the reduction of CO2 and CO as feedstock gases. The catalytic system performs best (referring to the TON of CH4 production) for CO as a feedstock.
Catalysts
Photosensitizers
5,10-Di(2-naphthyl)-5,10-dihydrophenazine
3,7-Di((1,1'-biphenyl)-4-yl)-10-(naphthalen-1-yl)-10H-phenoxazine
Investigations
| cat | cat conc [µM] | PS | PS conc [mM] | e-D | e-D conc [M] | solvent A | additives | . | . | λexc [nm] | . | TON CO | TON CH4 | TON H2 | . | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1. | 0.01 | 1 | 0.1 | > 435 | 50 | 8 | 8 | |||||||||
| 2. | 0.01 | 1 | 0.1 | TFE | > 435 | 71 | 14 | 10 | ||||||||
| 3. | 0.01 | 1 | 0.1 | TFE | > 435 | 140 | 29 | 23 |
| cat | cat conc [µM] | PS | PS conc [mM] | e-D | e-D conc [M] | solvent A | additives | . | . | λexc [nm] | . | TON CH4 | TON H2 | . | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1. | 0.01 | 1 | 0.1 | Visible light (>435) | 10 | 21 | |||||||||
| 2. | 0.01 | 1 | 0.1 | TFE | Visible light (>435) | 45 | 7 | ||||||||
| 3. | 0.01 | 1 | 0.1 | TFE | Visible light (>435) | 21 | 9 | ||||||||
| 4. | 0.01 | 1 | 0.1 | TFE | Visible light (>435) | 39 | 7 | ||||||||
| 5. | 0.01 | 1 | 0.1 | TFE | Visible light (>435) | 46 | 8 | ||||||||
| 6. | 0.01 | 1 | 0.1 | TFE | Visible light (>435) | 80 | 14 | ||||||||
| 7. | 0.01 | 1 | 0.1 | TFE | Visible light (>435) | 27 | 17 | ||||||||
| 8. | 0.01 | 1 | 0.1 | TFE | Visible light (>435) | 17 | 37 | ||||||||
| 9. | 0.01 | 1 | 0.1 | water | Visible light (>435) | 10 | 5 | ||||||||
| 10. | 0.01 | 1 | 0.1 | water | Visible light (>435) | 12 | 6 | ||||||||
| 11. | 0.01 | 1 | 0.1 | PhOH | Visible light (>435) | 26 | 44 |
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.
Investigations
- Photocatalytic reduction of CO (Molecular process, Photocatalytic CO2 conversion experiments)
- Photocatalytic reduction of CO2 (Molecular process, Photocatalytic CO2 conversion experiments)
