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

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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

1. REDIRECT Photocatalytic reduction of CO2: conditions optimization

Experiment-Name: Table 1Export

1. REDIRECT Toward Visible-Light Photochemical CO2‑to-CH4 Conversion in Aqueous Solutions Using Sensitized Molecular Catalysis/Cyclic voltammetry in various conditions

Experiment-Name: Table 2 - CVExport

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.