Efficient and selective photocatalytic conversion of low- concentration CO 2 to CO using Mn catalysts Kei Kamogawa , Osamu Ishitani Department of Chemistry, Graduate School of Advanced Science and Engineering, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739 8526, Japan In recent years, a variety of photocatalysts for CO 2 reduction have been developed with the aim of converting CO 2 into valuable resources using light energy. However, the catalytic activity of these systems has been mostly evaluated under a pure CO 2 atmosphere. In contrast, the CO 2 concentration of exhaust gases from industries and thermal power stations ranges from a few to 20%, and enriching such dilute CO 2 requires additional cost and energy. Therefore, the development of photocatalytic systems that can maintain high activity even under low CO 2 concentrations is strongly desired. Mn is one of the most abundant metals, and fac -[Mn I (diimine)(CO) 3 L] n+ complexes have been extensively studied as electrocatalysts for CO 2 reduction. 1,2 However, their application in photocatalytic CO 2 reduction is still limited due to the formation of photochemically unstable Mn(0) dimers, [Mn 2 (diimine) 2 (CO) 6 ]. 3 As a result, the performance of Mn(I)-based photocatalytic CO 2 reduction systems has not yet been evaluated under low CO 2 concentrations. In this work, we synthesized a novel Mn(I) complex by introducing a sterically bulky mesityl group at the 6-position of the 4,4'-dimethyl-2,2'-bipyridineligand and used it as a catalyst in photocatalytic reactions. In the presence of trifluoroethanol (TFE) and diisopropylethylamine, the Mn complex captures CO 2 to form the corresponding carbonate ester complex ( MnMes-CO 2 TFE ). In combination with a TADF organic photosensitizer, MnMes- CO 2 TFE selectively reduces CO 2 to CO and demonstrates excellent photocatalytic durability owing to the complete suppression of Mn dimer formation. The turnover numberof CO formation reached a maximum of 8770 based on the MnMes-CO 2 TFE used. Furthermore, MnMes-CO 2 TFE exhibited high selectivity and catalytic rates for CO production,even at low CO 2 concentrations, attributed to the efficient CO 2 capture reaction in the presence of TFE.Under 10% and 1% CO 2 atmospheres, the turnover frequencies for CO production (TOF CO ) are 5.31 and 2.66 min ‒1 , respectively, corresponding to 88% and 44% of TOF CO under 100% CO 2 conditions (6.03 min ‒1 ).To the best of our knowledge, this is the first photocatalytic system that uses only Earth-abundant elements for the reduction of low-concentration CO 2 based on CO 2 capture by a catalyst molecule. References 1. M. Bourrez, F. Molton, S. Chardon-Noblat and A. Deronzier, Angew. Chem. Int. Ed. , 2011, 50 , 9903-9906. 2. J. M. Smieja, M. D. Sampson, K. A. Grice, E. E. Benson, J. D. Froehlich and C. P. Kubiak, Inorg. Chem. , 2013, 52 , 2484- 2491. 3. H. Koizumi, Y. Tamaki, K. Kamogawa, M. Nicaso, Y. Suzuki, Y. Yamazaki, H. Takeda and O. Ishitani, J. Am. Chem. Soc. , 2025, 147 , 6236-6248.
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