Light-Driven Reduction of CO2 to CO in Water with a Cobalt Molecular Catalyst and an Organic Sensitizer

Abstract

Summary

A photochemical reduction of CO₂ to CO was shown using the cobalt complex [Co(qpy)(H2O)2][ClO4]2 (100788) as a catalyst in combination with the organic, water soluble triazatriangulenium photosensitizer (100797). Turnover numbers (TONs) up to 19000 and selectivity of 93% for CO were reached in acetonitrile with 20% of water. The experiments were conducted under visible-light irradiation (λ > 450 nm) using tertiary amines or BIH as sacrificial reductants (see section SEDs below). The photoreduction could also be shown in pure water.

Advances and special progress

The photoreduction of CO₂ to CO could be shown in 100% water with a TON of 2600 and a selectivity of 94% without any noble metals or rare materials.

Additional remarks

In initial experiments, CO and formate were first produced with a total TON >3700 upon irradiation in CO₂-saturated CH₃CN solution with visible light. The addition of water enhanced the catalysis and directed it toward CO production (19,000 TON, 93% selectivity).

Content of the published article in detail

The article contains results for the reduction of CO₂ to CO under visible-light catalysis using a cobalt complex as a catalyst. The catalytic system performs best (referring to the TON of CO production) in acetonitrile with 20% water using BIH and TEOA.

Catalyst

[Co(qpy)(H2O)2][ClO4]2 (100788) CoCl2 (100798)

Photosensitizer

(100797)

Investigations

		cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	.	.	additives	λexc [nm]	TON CO	TON H2	TON HCOOH	.	.
(edit)	1.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1	MeCN				450	2332	106	1370
(edit)	2.			Molecule:100797	0.2	BIH	0.1	MeCN				450	0	0	0
(edit)	3.	[Co(qpy)(H2O)2][ClO4]2	0.002			BIH	0.1	MeCN				450	0	0	0
(edit)	4.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2			MeCN				450	950	86	316
(edit)	5.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1	MeCN				450	107	7	5
(edit)	6.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1	MeCN			Argon atmosphere	450	0	7	0
(edit)	7.	CoCl2	0.005	Molecule:100797	0.2	BIH	0.1	MeCN				450	0	159	0
(edit)	8.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1	MeCN			Hg (0.1 mL)	450	1880	255	1973

Investigation-Name: Visible-Light Driven CO2 Reduction with 1/TATA+/BIH + TEOA under Various Conditions

		cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	.	.	solvent A	.	.	additives	λexc [nm]	TON CO	TON H2	TON HCOOH	.	.
(edit)	1.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN				450	2332	106	1370
(edit)	2.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN				450	6228	304	2441
(edit)	3.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN				450	14691	283	1097
(edit)	4.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN				450	15822	220	1147
(edit)	5.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN				450	18989	227	1215
(edit)	6.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN			Hg	450	19646	226	415
(edit)	7.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN				450	183	9	419
(edit)	8.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN				450	612	202	51
(edit)	9.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN				450	515	253	46
(edit)	10.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN				450	3171	498	179
(edit)	11.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN				450	6331	264	179
(edit)	12.	[Co(qpy)(H2O)2][ClO4]2	0.002	Molecule:100797	0.2	BIH	0.1			MeCN			Hg	450	6286	304	97

Investigation-Name: Photocatalytic CO2 Reduction by 1 (2 μM) in CO2-Saturated Aqueous CH3CN Solutions

Sacrificial electron donor

In this study, the experiments were done with the sacrificial reductants TEOA (100507), BIH (100508), and TEA (100505).

Additives

In this study, some experiments were conducted under argon atmosphere or with the addition of Hg.