Toward Visible-Light Photochemical CO2‑to-CH4 Conversion in Aqueous Solutions Using Sensitized Molecular Catalysis

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DOI 10.1021/acs.jpcc.8b00950
Authors Heng Rao, Julien Bonin, Marc Robert,
Submitted 28.04.2018
Published online 28.04.2018
Licenses -
Subjects Surfaces, Coatings and Films, Physical and Theoretical Chemistry, General Energy, Electronic, Optical and Magnetic Materials
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Abstract

Summary

A photochemical reduction of CO2 was achieved using an iron porphyrin catalyst and an iridium complex as the photosensitizer. Carbon monoxide, produced with a TON of 178 under optimized conditions, was the main product, methane was produced in a substantial amount with the TON of 32, while hydrogen was formed as a minor byproduct. The experiments were performed under irradiation with λ > 420 nm in acetonitrile and in the presence of various amines as sacrificial electron donors.

Advances and special progress

The catalytic reduction of CO2 could also be realized under aqueous conditions (acetonitrile/water 3:7 v:v), yielding carbon monoxide as the main product while methane was produced with selectivity up to 10% (3 TON).

Additional remarks

Among the various amines employed as sacrificial electron donors, TEA appeared as the best choice to maximize CO2 product formation.

Content of the published article in detail

The article contains results for the reduction of CO2 to CO as the main product under visible-light irradiation using iron porphyrin complex Fe(pTMAPP)Cl5 (Fe(pTMAPP)Cl5) as the catalysts, an iridium complex as the photosensitizer and various amines as the sacrificial electron donor. The catalytic system performs best (referring to the TON of CO production) with Ir(ppy)3 (Ir(ppy)3) as the photosensitizer and TEA as the sacrificial electron donor.

Catalyst

Fe(pTMAPP)Cl5

Photosensitizer

[Ir(ppy)2(bpy)][PF6] Ir(ppy)3

Investigation

catcat conc [µM]PSPS conc [mM]e-De-D conc [M]solvent A.additives..λexc [nm].TON COTON CH4TON H2.
1.

Fe(pTMAPP)Cl5

0.002

[Ir(ppy)2(bpy)][PF6]

0.2

TEA

0.05

MeCN

> 42017832103
2.

Fe(pTMAPP)Cl5

0.002

[Ir(ppy)2(bpy)][PF6]

0.2

TEOA

0.05

MeCN

> 4201342367
3.

Fe(pTMAPP)Cl5

0.002

[Ir(ppy)2(bpy)][PF6]

0.2

DIPEA

0.05

MeCN

> 4201512477
4.

Fe(pTMAPP)Cl5

0.002

[Ir(ppy)2(bpy)][PF6]

0.2

TEA

0.05

MeCN

> 4202435
5.

Fe(pTMAPP)Cl5

0.002

[Ir(ppy)2(bpy)][PF6]

0.2

TEOA

0.05

MeCN

> 4201934
6.

Fe(pTMAPP)Cl5

0.002

[Ir(ppy)2(bpy)][PF6]

0.2

DIPEA

0.05

MeCN

> 4202034
7.

Fe(pTMAPP)Cl5

0.002

Ir(ppy)3

0.2

TEA

0.05

MeCN

> 4201983124
8.

Fe(pTMAPP)Cl5

0.002

Ir(ppy)3

0.2

TEA

0.05

MeCN

> 4208918
9.

Fe(pTMAPP)Cl5

0.002

Ir(ppy)3

0.2

TEA

0.05

MeCN

TFE> 42010019
10.

Fe(pTMAPP)Cl5

0.002

Ir(ppy)3

0.2

TEA

0.05

MeCN

TFE> 42019545
analyteanl conc [mM]reduction potentialsolventelectrolyte..gas.WE..RE.
1.

[Ir(ppy)2(bpy)][PF6]

0.5

-2.0 , -1.4

MeCN

TBAPF6

argonglassy carbonSCE
2.

[Ir(ppy)2(bpy)][PF6]

0.5

-2.0, -1.4

MeCN

TBAPF6

COglassy carbonSCE
3.

[Ir(ppy)2(bpy)][PF6]

0.5

-2.0, -1.4

MeCN

TBAPF6

COglassy carbonSCE
4.

[Ir(ppy)2(bpy)][PF6]

0.5

-2.0, -1.4

MeCN

TBAPF6

COglassy carbonSCE
5.

[Ir(ppy)2(bpy)][PF6]

0.5

-2.0

MeCN

TBAPF6

COglassy carbonSCE

The results show an increase in current when the solution is irradiated and triethylamine (TEA) is added (see condition column).

Sacrificial electron donor

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

Additives

In some experiments described in this study, TFE (TFE) was used as an additive.

Investigations