Luminescent Hybrid Materials for Photocatalysis and Sensing
Final Report Abstract
Microporous materials containing several active sites within one framework (multi-functionalized materials), are of tremendous importance for many applications. Especially for application in heterogeneous catalysis and sensing the rational design of those materials allow introducing a large variety of functional groups. However little is known on the influence of pore wall composition, pore geometry and pore size on the properties of a molecular species bound to the pore. The objective of this project was to understand the effects which influence the properties of bound molecules by using different cutting edge analytical techniques and to translate these findings in general rules allowing to synthesis ever better performing materials demonstrated for photochemical CO2 reduction into value-added C1-molecules. By using X-ray photoelectron spectroscopy, the electron density on the active site in Rh-functionalized microporous materials was determined and correlated to the catalytic activity of those materials in photochemical CO2 reduction. This allowed to identify the Hammett principle as important structureproperty relationship. The Hammett principle correlates directly the electron density on the active site of a catalyst with its catalytic activity. These findings necessitate a reevaluation of the understanding of microporous materials, including metal-organic frameworks and porous organic polymers, as host materials. They can no longer be seen as innocent host materials, fixing the active site and only causing confinement effects. Instead, they have to be seen as macroligands, influencing in a predictable way the electron density on the active site. This finding is backed by results from DNP SENS MAS NMR spectroscopy and PDF analysis, giving for the first time important insights into the molecular structure of heterogenized complexes within amorphous materials. Moreover, this concept allows to distinguish whether or not confinement effects have to be considered, by directly comparing the activity of heterogenized catalyst with homogeneous catalysts, and to rationally design ever better performing heterogeneous catalysts, finally with the goal to outperform standard homogeneous catalysts. Within the frame of this project this has been demonstrated for a variety of catalytic reactions such as photocatalytic CO2 reduction, transfer hydrogenation reactions or ethylene dimerization. New multi-functionalized heterogeneous catalysts for the photocatalytical reduction of CO2 were designed following the Hammett correlation for those macroligands. Porous organic frameworks were chosen as macroligands, as they have more favorable electronic donating properties as compared to metal-organic frameworks, thus resulting in higher activities of the catalyst. By integrating organic dyes as photosensitizer into the polymers backbone, for the first time a heterogeneous catalyst was obtained that produces formiate with a constant rate for up to 100 h. In the future, analytical techniques such as time resolved spectroscopy or further solid-state NMR techniques could be used to further investigate the influence of confinement on active sites inside those macroligands. Most importantly, the Hammett concept will help in the future to rationally design new macroligands, thus further reducing the gap between homogeneous and heterogeneous catalysis and finally obtaining heterogeneous catalysts as active as their well-studied homogeneous counterparts.
Publications
- “Sensitive Photo acoustic IR-Spectroscopy for the Characterization of Amino/Azido Mixed-Linker Metal-Organic Frameworks”, Chem- PhysChem 2017, 18, 2855-2858
J. Canivet, V. Lysenko, J. Lehtinen, A. Legrand, F. M. Wisser, E. A. Quadrelli, D. Farrusseng
(See online at https://doi.org/10.1002/cphc.201700663) - “Hammett parameter in microporous solids as macroligands for heterogenized photocatalysts”, ACS Catal. 2018, 8, 1653-1661
F. M. Wisser, P. Berruyer, L. Cardenas, Y. Mohr, E. A. Quadrelli, A. Lesage, D. Farrusseng, J. Canivet
(See online at https://doi.org/10.1021/acscatal.7b03998) - “Immobilization of a full photosystem in the large pore MIL‐101 Metal‐Organic Framework for CO2 reduction”, ChemSusChem
X. Wang, F. M. Wisser, J. Canivet, M. Fontecave, C. Mellot-Draznieks
(See online at https://doi.org/10.1002/cssc.201801066) - “Microporous polymers as macroligands for Cp*Rh transfer hydrogenation catalysts”, ChemCatChem 2018, 10, 1778-1782
F. M. Wisser, Y. Mohr, E. A. Quadrelli, D. Farrusseng, J. Canivet
(See online at https://doi.org/10.1002/cctc.201701836)
