2016 Fiscal Year Annual Research Report
Development of hybrid photocatalysts with metal complexes and semiconductor for CO2 reduction
| Project/Area Number |
16F16336
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
石谷 治 東京工業大学, 理学院, 教授 (50272282)
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| Co-Investigator(Kenkyū-buntansha) |
FABRY DAVID 東京工業大学, 理学院, 外国人特別研究員
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| Project Period (FY) |
2016-11-07 – 2019-03-31
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| Keywords | 光触媒 |
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| Outline of Annual Research Achievements |
Manganese CO2-reduction catalyst usually bear an aromatic diamine ligand that allows sensitive modification of the reaction mechanism. Typically, bipyridine allows the one-electron reduced Mn-species to dimerize, from which formic acid (HCOOH) is majorly produced. This, however, poses certain difficulties as the Mn0-Mn0 dimer absorbs in the visible light region which can lead to catalyst degradation.
To avoid any Mn-dimer formation and a simpler system to analyse, we installed sterically demanding groups on the Mn-diimine ligand periphery. This step prevents the reduced Mn-species to dimerise to a Mn0-Mn0 intermediate. Furthermore, any additional visible light absorption of Mn-catalyst would thereby be prevented.
Such a catalyst was successfully synthesized and together with a Ru-photosensitizer tested in CO2 reduction reactions. We found that in DMA-TEOA as common solvent combination the novel catalyst system produces formic acid (HCOOH) in high turn-over-numbers (TONs) reaching 100 after 6 hours, using dimethylphenylbenzimidazoline (BIH) as sacrificial electron donor. In situ FTIR-studies revealed a Mn-formate complex as key intermediate from which formate release occurs. In situ UV-Vis studies revealed that only little amount of electrons accumulated on the Ru-photosensitizer unit as one-electron reduced species (Ru-OERS) from which photosensitizer degradation occurs. This indicates that ruthenium and manganese are a suitable the combination for future supramolecular catalyst systems.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The project proceeded according to our expectations. After synthesis of the catalyst units, the photochemical performances could be analysed in short time. However, since the results indicated differences to similar catalysts performed in electrochemical fashion, more experiments were necessary to elucidate the origin of the inconsistency. Careful mechanistic studies revealed a different reaction pathway whose key intermediate could be identified and compared to previous reports. Since our catalyst apparently poses an exception to other manganese catalyst reports, this project nevertheless is of great importance to the research community.
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| Strategy for Future Research Activity |
In the previous year we could successfully show that a ruthenium photosensitizer and a bulky manganese CO2-reduction catalyst can work together for efficient CO2-HCOOH reduction with visible light. Not only high turn-over numbers around 100 after 6 hours were obtained, but in situ spectroscopy moreover revealed a stable catalyst system over the course of the reaction. As planned, the bulky substituents prevented any Mn-dimerization and a Mn-formate complex was found to be the crucial intermediate.
Having a robust photochemical system in hand, we want to extend this project to a supramolecular catalyst. In the past, our group could show with several examples that due to the direct chemical connection of both catalyst units via a bridging ligand, higher stability and efficiencies can be obtained. In the same fashion, the Ru-photosensitzer is ought to be connected to the manganese unit. Again, stabilities and photocatalytic performance shall be compared.
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