POM@MOF composites for photocatalytic CO2 reduction – PMCOCAT

One of the major challenges in the field of photocatalysis is the development of noble-metal free, efficient, selective and recyclable catalysts. By combining our complementary expertise, our consortium proposes to develop, characterize and study the properties of metal-organic framework (MOF) photosensitive hybrid materials containing in their cavities polyoxometalate (POM) molecular catalysts. The aim is to develop new heterogeneous catalysts efficient to reduce CO2 in gas phase, with water vapor as electron donor. The ligands used to build these photosensitive MOFs are porphyrin derivatives, which may be metalated, or benzenedicarboxylate linkers functionalized by amino groups. Calculations will allow to complete the study of the crystal structure of the materials, to study the electronic structure and to understand the mechanism of the catalytic reduction of CO2. Beyond the optimization of the catalyst and the photosensitizer, the emphasis will also be put on the structuration of the materials (elaboration of nanocrystals and of mesoporous structures) in order to optimize their active surface and to improve the diffusion of CO2 molecules.

Task 1 concerns the synthesis and characterization of new molecular POMs which will then be immobilized in crystallites of MOFs with amino linkers or of porphyrinic MOFs to lead to POM@MOF composites. For the best candidates, we will study the effect of structuration (nano and mesostructuration) on the rate of encapsulated POMs and then on their performances. The compounds will be characterized by X-ray powder diffraction, IR spectroscopy, specific surface area measurement, elemental analysis and electron microscopy. Task 2 will consist in the study of the photocatalytic properties of molecular POMs in homogeneous solution and POM@MOF compounds in suspension, then for the best performing materials in gas phase, on the unique facility recently installed at IFPEN. Particular attention will be paid to the study of the stability of the catalysts and their recyclability. Finally, task 3 will deal with computational chemistry allowing i) to propose possible localization sites of POMs in MOF pores and to apprehend the host/guest interactions, ii) to study the electronic structure of POM@MOFs compounds in order to identify the best (POMs, linkers) couples, in a screening type approach and iii) to compute catalytic pathways for the photocatalytic reduction of CO2 in selected systems. Thus, the collaborative and multidisciplinary PMCOCAT project will provide access to a family of new POM-based materials, without noble metals and without external photosensitizer, active for the photocatalytic reduction of CO2 coupled to water oxidation, and to propose structure/properties relationships through DFT calculations.