Tailor Made Heterogeneous Photocatalysts for Carbon Dioxide Reduction based on Microporous Macroligands

SSCI-VIDE+ING+FWI:JEC; International audience; Heterogeneous catalysis allows to circumvent the problem of separation of the catalyst from the products and to simplify its recyclability. The integration of the catalytically active centers into a solid support without loss of performance compared to the homogeneous analog is still a major challenge. In this context, a molecularly defined support as macroligand, i.e. a solid acting like the ligand in the corresponding molecular complex, can be considered as a key to bridge the gap between molecular and heterogeneous catalysis. In particular, porous frameworks made by the repetition of a coordinating motif, like the bipyridine motif are of a high interest as bipyridines are widely used as chelating ligand for molecular catalysts.[1]Amongst the catalytic applications, photochemical carbon dioxide reduction is of tremendous importance as routes to renewable energy sources. Here we present a series of heterogeneous catalysts based on metal-organic frameworks and microporous polymers used as macroligands for heterogenized organometallic complexes.[2] We show that both homogeneous and heterogenized catalysts follow the same linear correlation between the electronic effect of the ligand, described by the Hammett parameter, and the catalytic activity. This correlation highlights the crucial impact of the local electronic environment surrounding the active catalytic center over the long-range framework structure of the porous support. The rational design of heterogenized catalysts is demonstrated here for the photoreduction of carbon dioxide into formate with turnover frequencies up to 28 h−1, in the presence of a homogeneous photosensitizer.[2]We will also present completely heterogeneous photocatalysts to overcome the current limitation of photodegradation of the light harvesting moiety. In these systems both the photosensitizer and the catalyst are integrated into the same framework, either covalently to the backbone or by co-immobilized inside the pores. In the later case, the pores are used as nanoreactors, as the catalyst and photosensitizer are co-confined into the cavity’s nanospace and enable molecular catalysis in a heterogeneous manner.[3] This approach allows to develop a photocatalytic system that completely suppresses the hydrogen evolution typically observed as a side reaction. Finally, different photo-sensitizers will be evaluated in terms of their light absorption properties and the resulting catalytic activities.References:[1] a) A. Corma, H. García, F. X. Llabrés i Xamena Chem. Rev. 2010, 110, 4606-4655; b) C. Kaes, A. Katz, M. W. Hosseini Chem. Rev. 2000, 100, 3553-3590.[2] F. M. Wisser, P. Berruyer, L. Cardenas, Y. Mohr, E. A. Quadrelli, A. Lesage, D. Farrusseng, J. Canivet ACS Catal. 2018, 8, 1653-1661. [3] X. Wang, F. M. Wisser, J. Canivet, M. Fontecave, C. Mellot-Draznieks, ChemSusChem, 2018, 11, 3315-3322.