Succeeded in CO2 photoreduction reaction with renewable ruthenium complex at Ritsumeikan University and others

Ritsumeikan University, Kyoto University (Kyoto University), and Shizuoka Institute of Science and Technology (SIST) announced on February 3 that they have developed a renewable “organic hydride” with ligands modeled on natural redox coenzymes. It was announced that it was revealed for the first time that the “ruthenium complex” possessed by the compound can catalytically reduce carbon dioxide (CO 2 ) to the resource “formic acid” by irradiation with visible light.

Dr. Yusuke Kinoshita (Former Assistant Professor, Currently Specially Appointed Assistant Professor, Hokkaido University), Graduate School of Life Science, Ritsumeikan University, Specially Appointed Professor Koji Tanaka, Institute for Advanced Research, Kyoto University A joint research team including Professor Takeaki Koizumi of the SIST Advanced Instrument Analysis Center. The details were published in “ChemSusChem”, an academic journal that deals with the impact of chemistry on climate change in general, published by Chemistry Europe, in which 16 chemical organizations from 15 European countries participate.

Technology to remove CO 2 from the atmosphere using sunlight and at the same time to recycle it is expected as “artificial photosynthesis”, and research is progressing. One such technique uses light irradiation to chemically reduce CO 2 to convert it into resources such as formic acid and methane.

The problem with this method is that CO 2 is an extremely stable substance, so chemically reducing it to a useful resource requires a lot of energy using conventional methods. Therefore, the research team decided to mimic photosynthesis, in which plants easily reduce CO 2 using only sunlight.

In the in vivo reduction reaction, the nicotinamide site on the nicotinamide adenine dinucleotide (NAD + ) of the coenzyme accepts one proton and two electrons by external energy, resulting in reduced NADH. This NADH gives H  to the substrate for reduction, and itself is regenerated as oxidized NAD + . In this way, the NAD + /NADH redox pair participates in many redox reactions of organic substances in vivo, and performs material conversions with high efficiency without accompanying by-products.

In this study, they used a ruthenium complex modeled on the natural redox reaction coenzyme NAD + /NADH, and decided to use visible light energy for the catalytic CO 2 reduction reaction.

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