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

Abstract

Novel CO 2 -philic Pd complexes, PdCl 2 [4,4'-bis(R f CH 2 OCH 2 )-2,2'-bpy] (bpy: 2,2'-bipyridine) where R f = n-C 10 F 21 , n-C 11 F 23 , were anchored onto a silica support modified with long fluorinated hydrocarbon chains (C 6 F 13 ) by mixing these complex and the support in DMSO at 413 K. These immobilized Pd complex catalysts were applied for the photoreduction of CO 2 in DMF or organic solvents using triethylamine as a hydrogen donor at 323 K. The rate of CO 2 reduction and the selectivity to CO were observed to depend on several factors including CO 2 pressure, solvent, Pd complex structure, and Pd loading. With the most active catalyst, the selective photoreduction of CO 2 to CO can be achieved in DMF at a CO 2 pressure of 4 MPa and the performance observed is much better compared to the literature results. The features of the supported 2 Pd complexes and the multiphase reaction media were characterized by UV-Vis absorption and others to discuss the reasons for their high performance.

Recent Advances in Heterogeneous Photocatalytic CO2 Conversion to Solar Fuels

“…Some metal (Re, Ru, Co) complexes can also act as molecular cocatalysts of semiconductors for promoting the CO 2 reduction reactions. ,,,,− In this system, the photogenerated electrons of semiconductor can migrate to the loaded Ru/Re complexes, which is followed by the CO 2 reduction process, as shown in Figure a. It is well-known that molecular catalysts, especially carbonyl metal (Re, Ru, Co, Mn) bipyridyl complexes, are already employed in homogeneous CO 2 reduction systems with high quantum efficiency, and the CO 2 conversion mechanism over center metals is also understood. , However, one disadvantage of this system is the unavailability of H 2 O as electron donor under CO 2 photoreduction conditions.…”

“…It is well-known that molecular catalysts, especially carbonyl metal (Re, Ru, Co, Mn) bipyridyl complexes, are already employed in homogeneous CO 2 reduction systems with high quantum efficiency, and the CO 2 conversion mechanism over center metals is also understood. , However, one disadvantage of this system is the unavailability of H 2 O as electron donor under CO 2 photoreduction conditions. In contrast, a semiconducting photocatalyst can use H 2 O as an electron donor under the conditions used for photocatalytic CO 2 reduction. , Also, those molecular catalysts can be immobilized on solid materials such as g-C 3 N 4 , TiO 2 , N–Ta 2 O 5 , or even organosilica as light harvester to improve the performance of CO 2 reduction. ,,− In this heterogeneous CO 2 reduction system, the LUMO position is more positive than the CB level of the semiconductor, and therefore, the photoexcited electrons from the CB of the semiconductor can transfer to the metal-complex cocatalyst to promote the selective CO 2 reduction on the metal complex. For example, Meda’s group has reported such heterogeneous system consisting of Ru complex and g-C 3 N 4 , which acts as the catalytic and light-harvesting units, respectively, for CO 2 reduction to CHOOH. , Its photocatalytic performance can be improved by promoting the injection of electrons from g-C 3 N 4 into Ru-unit, strengthening the electronic interactions between the two units and using a suitable solvent. , Similarly, the light-harvesting property and activity of homogeneous molecular catalysts such as Re, Ru, Co, Pd, or Ru–Re binuclear complexes can be improved through immobilization on metal oxide. − To strengthen the electronic interactions between the two units, 4,4′-position of bipyridyl of the Re complex is functional with phosphate group to form an ester linkage with the surface hydroxyl of photocatalysts. ,, A similar tight linkage between the two units can provide an electron transfer gallery from a semiconductor to metal complexes and enhance the CO 2 reduction activity. , …”