Selective photoreduction of CO2 to CO in CO2-dissolved expanded liquid phase with heterogeneous CO2-philic Pd complex catalysts

Novel CO2-philic Pd complexes, PdCl2[4,4′-bis(RfCH2OCH2)-2,2′-bpy] (bpy: 2,2′-bipyridine) where Rf = n-C10F21, n-C11F23, were anchored onto a silica support modified with long fluorinated hydrocarbon chains (C6F13) by mixing these complex and the support in DMSO at 413 K. These immobilized Pd complex catalysts were applied for the photoreduction of CO2 in DMF or organic solvents using triethylamine as a hydrogen donor at 323 K. The rate of CO2 reduction and the selectivity to CO were observed to depend on several factors including CO2 pressure, solvent, Pd complex structure, and Pd loading. With the most active catalyst, the selective photoreduction of CO2 to CO can be achieved in DMF at a CO2 pressure of 4 MPa and the performance observed is much better compared to the literature results. The features of the supported Pd complexes and the multiphase reaction media were characterized by UV–vis absorption and others to discuss the reasons for their high performance.

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► Fluorinated Pd complexes are immobilized on the surface of fluorinated SiO2 support.
► The Pd catalysts are active for photoreduction of CO2 to CO in CO2 expanded liquids.
► The catalytic activities change depending on CO2 pressure and organic solvent used.
► The immobilized Pd complexes show the highest activity and 100% selectivity to CO.