2017 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 |
Works from our group not only studied the photocatalytic behavior of Ru- or Re-complexes for CO2-reduction, we moreover reported on supramolecular photocatalysts that showed superior performance over their mononuclear pendant. Such multinuclear complexes, now consisting of various combinations of photocatalyst and CO2 reduction unit in one catalyst, enabled directed and thus enhanced electron transfers leading to higher TONs and catalyst durability.
To study the interaction of photosensitizer and CO2 reduction unit, three catalysts with different Mn-to-Ru stoichiometry were prepared: Mn, Ru-Mn, Ru2-Mn. The dinuclear Ru-Mn catalyst could improve the rate of product formation dramatically due to enhanced and stabilized electron transfers across the bridging ligand. However, incorporating two photosensitizer units led to lower stability and fast catalyst decomposition. In situ UV-Vis studies revealed that electrons accumulated on the Ru-photosensitizer unit as one-electron reduced species (Ru-OERS) that led to ligand detachment and consecutive decomposition of the dinuclear catalyst. Eventually, this process could be stabilized by adjusting the light intensity to the speed of the CO2-reduction so that all generated Ru-OERS are immediately consumed by the Mn-unit.
In summary, the synthesis and characterisation of novel supramolecular Ru(II)-Mn(I) catalysts for photocatalytic CO2-reduction was presented. Overall, better catalyst performances could be obtained from the supramolecular catalyst compared to the individual catalyst system.
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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 synthesized supramolecular Ru(II-Mn(I) catalyst is the first example of its kind. Based on our previous studies, the results show highly promising data for future applications. During the photochemical reactions, we observed a unique influence of the light intensity. In contrast to previous findings, lower light intensities stabilized the catalyst and gave higher turn-over numbers than high light intensities. This rather exceptional situation was carefully analyzed and validated by structural catalyst modifications. Eventually, a profound understanding of the catalyst and its light intensity behavior was obtained. With this understanding in mind, the next step towards a hybrid system can be made.
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| Strategy for Future Research Activity |
In the following month, the synthesis of the supramolecular catalyst with additional phosphonic acid groups will be accomplished to ensure a stable adsorption on the semiconductor. With the novel hybrid catalyst in hand, photocatalytic reactions will be performed and compared to the individual catalyst systems. Mechanistic studies will be conducted to investigate potential alterations of reaction pathways due to the semiconductor-interaction on the surface. Finally, the long-term stability of the novel system will be tested, as well as desorption effects of the molecular catalyst.
Moreover, the Ru(II)-Mn(I)-PO3H2 catalyst can be attached to electrodes to allow a photo-electrochemical transformation of CO2-HCOOH together with potential oxidation reactions. Both applications would be of high value for the research community, as the replacement of late-transition metals is of tremendous importance in the pursue to establish a sustainable fuel-production in the future.
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