Photocatalytic Reduction of Carbon Dioxide to CO and HCO2H Using fac-Mn(CN)(bpy)(CO)3

Abstract

Summary

A photochemical reduction of CO₂ to CO or formic acid was shown and investigated using the manganese complex Mn(CN)(bpy)(CO)3 as catalyst in combination with the ruthenium-based photosensitizer [Ru(dmb)3][PF6]2. Turnover numbers (TONs) of 21 for CO and 127 for formic acid were reached, depending on the solvent mixture. CO was preferably formed in acetonitrile/TEOA, formic acid was generated as the main product in a mixture of DMF/TEOA. The experiments were conducted under visible-light irradiation (λ = 470 nm) using TEOA or BNAH as sacrificial electron donors (see section SEDs below).

Advances and special progress

The authors have expanded the knowledge on the photocatalytic reduction of CO₂ with a manganese complex and a ruthenium photosensitizer by exploring the solvent-dependent reduction to CO or formic acid and the stability of the involved complexes in these solvents.

Additional remarks

The formation of CO or formic acid could be found to be dependent on the solvent mixture and the concentrations of the catalyst and photosensitizer. Moreover, DMF was found to generate measurable amounts of formic acid in the presence of TEOA in the dark independent of the actual photocatalytic CO₂ reduction.

Content of the published article in detail

The article contains results for the reduction of CO₂ to CO or formic acid under visible-light catalysis using a manganese complex as a catalyst. The catalytic system performs best (referring to the TON of CO production) in acetonitrile/TEOA.

Catalyst

Mn(CN)(bpy)(CO)3

Photosensitizer

[Ru(dmb)3][PF6]2

Investigation

	cat	cat conc [µM]	PS	PS conc [mM]	e-D	e-D conc [M]	solvent A	.	.	λexc [nm]	.	TON CO	.	TON H2	TON HCOOH	.	.	.
1.	Mn(CN)(bpy)(CO)3	0.1	[Ru(dmb)3][PF6]2	0.1	BNAH	0.1	DMF			470		3.9		0.64	36
2.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF			470		3.2		0.45	21
3.	Mn(CN)(bpy)(CO)3	1	[Ru(dmb)3][PF6]2	1	BNAH	0.1	DMF			470		2.3		0.37	9.5
4.	Mn(CN)(bpy)(CO)3	0.1	[Ru(dmb)3][PF6]2	0.1	BNAH	0.1	DMF			470		2.8		0.2	16
5.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF			470		0.92		0.25	11
6.	Mn(CN)(bpy)(CO)3	1	[Ru(dmb)3][PF6]2	1	BNAH	0.1	DMF			470		0.83		0.0073	5.2
7.	Mn(CN)(bpy)(CO)3	0.1	[Ru(dmb)3][PF6]2	0.1	BNAH	0.1	MeCN			470		7.9		0.56	4.5
8.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	MeCN			470		5.9		0.24	2.1
9.	Mn(CN)(bpy)(CO)3	1	[Ru(dmb)3][PF6]2	1	BNAH	0.1	MeCN			470		3.2		0.17	1.2
10.	Mn(CN)(bpy)(CO)3	0.1	[Ru(dmb)3][PF6]2	0.1	BNAH	0.1	MeCN			470		4.7		0.27
11.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	MeCN			470		3.4		0.14
12.	Mn(CN)(bpy)(CO)3	1	[Ru(dmb)3][PF6]2	1	BNAH	0.1	MeCN			470		3.1		0.14
13.	Mn(CN)(bpy)(CO)3	0.1	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF			470		9.1		1.2	130
14.	Mn(CN)(bpy)(CO)3	0.1	[Ru(dmb)3][PF6]2	1	BNAH	0.1	DMF			470		7.1		1.6	130
15.	Mn(CN)(bpy)(CO)3	1	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF			470		3		0.24	5.8
16.	Mn(CN)(bpy)(CO)3	0.1	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	MeCN			470		19		1.4	8.1
17.	Mn(CN)(bpy)(CO)3	0.1	[Ru(dmb)3][PF6]2	1	BNAH	0.1	MeCN			470		21		1.3	9
18.	Mn(CN)(bpy)(CO)3	1	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	MeCN			470		4.2		0.8	1.4

Experiment-Name: Table 1Export

	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	.	.	.
1.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2		BNAH	0.1	DMF				470		2.1			1.9
2.	Mn(CN)(bpy)(CO)3		[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF				470		1.5		2.8	5.7
3.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF				470		5.8		0.26
4.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF			Argon gas	470					2.6
5.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF			Argon gas	470		1.5		7.8	3.8
6.	Mn(CN)(bpy)(CO)3		[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF			Argon gas	470		0.87		1.3	3.2
7.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2		BNAH	0.1	DMF			Argon gas	470		2.3			2.2
8.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF			Argon gas	470		2.4		1.4
9.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2		BNAH	0.1	DMF				470		2
10.	Mn(CN)(bpy)(CO)3		[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF				470		0.60		1.2	0.72
11.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF				470		2.2
12.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF			Argon gas	470		2.2		4.4	0.55
13.	Mn(CN)(bpy)(CO)3	0.5	[Ru(dmb)3][PF6]2	0.5	BNAH	0.1	DMF			Argon gas	470		2.4		1.4

Experiment-Name: Table 2Export

Sacrificial electron donor

In this study, the experiments were done with the sacrificial electron donors TEOA (100507) and BNAH (BNAH).

Additives

In this study, control experiments under argon atmosphere were conducted.