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

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

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

	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.	Fe(pTMAPP)Cl5	0.01	Molecule:100493	1	TEA	0.1	DMF				> 435		50	8	8
2.	Fe(pTMAPP)Cl5	0.01	Molecule:100493	1	TEA	0.1	DMF	TFE			> 435		71	14	10
3.	Fe(pTMAPP)Cl5	0.01	Molecule:100493	1	TEA	0.1	DMF	TFE			> 435		140	29	23

Investigation-Name: Photocatalytic reduction of CO2Export

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.