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Fighting climate change: Ruthenium complexes for carbon dioxide reduction to valuable chemicals

A novel technology facilitates hydride transfer to carbon dioxide, converting it into formic acid at a high turnover number

Date:
February 9, 2023
Source:
罗切斯特理工学院的航拍sumeikan University
Summary:
Excessive use of fossil fuels leads to undesired carbon dioxide (CO2) generation, accelerating climate change. One way to tackle this is by converting CO2 into value-added chemicals. On this front, researchers have recently utilized a novel redox couple, for the purpose.
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FULL STORY

气候变化是一个全球性的环境问题。A major contribution to climate change comes from excessive burning of fossil fuels. They produce carbon dioxide (CO2), a greenhouse gas responsible for global warming. In this light, governments globally are framing policies to curb such carbon emissions. However, merely curbing carbon emissions may not be enough. Managing the generated carbon dioxide is also necessary.

On this front, scientists have suggested chemically converting CO2into value-added compounds, such as methanol and formic acid (HCOOH). Producing the latter requires a source of hydride ion (H-), which is equivalent to one proton and two electrons. For instance, the nicotinamide adenine dinucleotide (NAD+/NADH) reduction-oxidation couple is a hydride (H-) generator and reservoir in biological systems.

Against this backdrop, a group of researchers led by Professor Hitoshi Tamiaki from Ritsumeikan University, Japan, have now developed a novel chemical method that reduces CO2to HCOOH using NAD+/NADH-like ruthenium complexes. Their work was published in the journalChemSusChemon 13 January 2023.

Prof. Tamiaki explains the motivation behind their research. "Recently, a ruthenium complex with an NAD+model -- [Ru(bpy)2(pbn)](PF6)2-- was shown to undergo photochemical two-electron reduction. It produced the corresponding NADH-type complex [Ru(bpy)2(pbnHH)](PF6)2under visible light irradiation in the presence of triethanolamine in acetonitrile (CH3CN)," he elaborates. "Further, the bubbling of CO2into the [Ru(bpy)2(pbnHH)]2+solution regenerated [Ru(bpy)2(pbn)]2+and produced formate ion (HCOO-). However, its yield was quite low. Therefore, transferring H-to CO2required an improved catalytic system."

Consequently, the researchers explored various reagents and reaction conditions to facilitate CO2reduction. Based on those experiments, they proposed a photoinduced two-electron reduction of the [Ru(bpy)2(pbn)]2+/[Ru(bpy)2(pbnHH)]2+redox couple in the presence of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH). Moreover, water (H2O), instead of triethanolamine, in CH3CN further improved the yield.

In addition, the researchers explored the underlying reaction mechanism using techniques like nuclear magnetic resonance, cyclic voltammetry, and UV-Vis spectrophotometry. Based on this, they proposed the following: First, the photo-excitation of [Ru(bpy)2(pbn)]2+produces [RuIII(bpy)2(pbn•?)]2+* radical, which undergoes reduction by BIH to give [RuII(bpy)2(pbn•?)]2+and BIH•+. Following this, H2O protonates the ruthenium complex, generating [Ru(bpy)2(pbnH•)]2+and BI•. The obtained product undergoes disproportionation to generate [Ru(bpy)2(pbnHH)]2+and gives back [Ru(bpy)2(pbn)]2+. Then, the former is reduced by BI• to produce [Ru(bpy)(bpy•?)(pbnHH)]+. This complex is an active catalyst and transfers H-to CO2, producing HCOO-and formic acid.

The researchers showed that the proposed reaction demonstrated a high turnover number -- moles of CO2converted by a mole of catalyst -- of 63.

Excited by these findings, the researchers hope to develop a new methodology of energy conversion (sunlight to chemical energy) for the production of novel renewable materials.

"Our method would also decrease the total amount of CO2gas on Earth and help maintain the carbon cycle. Thus, it could reduce global warming in the future," adds Prof. Tamiaki. "Further, the novel organic hydride transfer technology will provide us with invaluable chemical compounds."

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Materialsprovided by罗切斯特理工学院的航拍sumeikan University.Note: Content may be edited for style and length.


Journal Reference:

  1. Yusuke Kinoshita, Nagisa Deromachi, Takashi Kajiwara, Take‐aki Koizumi, Susumu Kitagawa, Hitoshi Tamiaki, Koji Tanaka.Photoinduced Catalytic Organic‐Hydride Transfer to CO 2 Mediated with Ruthenium Complexes as NAD + /NADH Redox Couple Models**.ChemSusChem, 2023; DOI:10.1002/cssc.202300032

Cite This Page:

罗切斯特理工学院的航拍sumeikan University. "Fighting climate change: Ruthenium complexes for carbon dioxide reduction to valuable chemicals: A novel technology facilitates hydride transfer to carbon dioxide, converting it into formic acid at a high turnover number." ScienceDaily. ScienceDaily, 9 February 2023. /releases/2023/02/230209094129.htm>.
罗切斯特理工学院的航拍sumeikan University. (2023, February 9). Fighting climate change: Ruthenium complexes for carbon dioxide reduction to valuable chemicals: A novel technology facilitates hydride transfer to carbon dioxide, converting it into formic acid at a high turnover number.ScienceDaily. Retrieved August 15, 2023 from www.koonmotors.com/releases/2023/02/230209094129.htm
罗切斯特理工学院的航拍sumeikan University. "Fighting climate change: Ruthenium complexes for carbon dioxide reduction to valuable chemicals: A novel technology facilitates hydride transfer to carbon dioxide, converting it into formic acid at a high turnover number." ScienceDaily. www.koonmotors.com/releases/2023/02/230209094129.htm (accessed August 15, 2023).

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