Photoreduction of CO₂ Using [Ru(bpy)₂(CO)L]ⁿ⁺ Catalysts in Biphasic Solution/Supercritical CO₂ Systems

Abstract

The reduction of CO 2 in a biphasic liquid-condensed gas system was investigated as a function of the CO 2 pressure. Using 1-benzyl-1,4-dihydronicotinamide (BNAH) as sacrificial electron donor dissolved in a dimethylformamide−water mixture and [Ru(bpy) 2 (CO)L]n+ as a catalyst and [Ru(bpy) 3 ]2+ as a photosensitizer, the reaction was found to produce a mixture of CO and formate, in total about 250 μmol after just 2 h. As CO 2 pressure increases, CO formation is greatly favored, being four times greater than that of formate in aqueous systems. In contrast, formate production was independent of CO 2 pressure, present at about 50 μmol. Using TEOA as a solvent instead of water created a single-phase supercritical system and greatly favored formate synthesis, but similarly increasing CO 2 concentration favored the CO catalytic cycle. Under optimum conditions, a turnover number (TON) of 125 was obtained. Further investigations of the component limits led to an unprecedented TON of over 1000, and an initial turnover frequency (TOF) of 1600 h −1.

trans‐(Cl)‐[Ru(5,5′‐diamide‐2,2′‐bipyridine)(CO)2Cl2]: Synthesis, Structure, and Photocatalytic CO2 Reduction Activity

“…It should be noted that the electrochemical reduction of the trans‐ (Cl)‐[Ru(bpy)(CO) 2 Cl 2 ]‐type complex dissociates chloride ions22 and the catalyst does not react with CO 2 until it receives a second electron 20–24. Although the evaluation of the reduction potential of the two‐electron‐reduced catalysts might be required, it is difficult to estimate the potential due to successive chemical reactions, such as dimerization and polymerization, of the reduced catalysts 22.…”

“…BNAH is known to promote the reductive quenching of the excited state of [Ru(bpy) 3 ] 2+ to generate the one‐electron reduced species of the photosensitizer ([Ru(bpy) 3 ] + ) 18. 19a, 20 Thus, two molecules of the one‐electron reduced species, [Ru(bpy) 3 ] + , would supply two electrons to the catalyst for CO 2 reduction 18. 21…”

Metal–Organic Framework (MOF) Compounds: Photocatalysts for Redox Reactions and Solar Fuel Production

“…[130] Theb ehavior of discrete molecular complexes inspired modification of MOF-253 to incorporate Ru carbonyl complex, giving MOF-253-Ru(CO) 2 Cl 2 that was tested as photocatalyst for CO 2 reduction under visible-light irradiation in am ixture of MeCN/ TEOA( 10/1). [130] Theb ehavior of discrete molecular complexes inspired modification of MOF-253 to incorporate Ru carbonyl complex, giving MOF-253-Ru(CO) 2 Cl 2 that was tested as photocatalyst for CO 2 reduction under visible-light irradiation in am ixture of MeCN/ TEOA( 10/1).…”

Photocatalytic reduction of CO 2 by Pt-loaded TiO 2 in the mixture of sub- and supercritical water and CO 2

“…Accordingly, the increase of the conversion efficiency will be expected, if the photocatalytic reduction of CO 2 is conducted in the single phase mixture of supercritical water and CO 2 . Although a few groups have reported the photocatalytic reduction of CO 2 in supercritical CO 2 or biphasic liquid/supercritical CO 2 system under gentle reaction conditions [16][17][18][19][20][21], it has never been studied in the single phase mixture of supercritical water and CO 2 . In this study, we have conducted the photocatalytic reduction of CO 2 with water by Pt-loaded TiO 2 (Pt/TiO 2 ) in the mixture of CO 2 and water as a function of temperature and pressure up to 400°C and 30 MPa beyond the critical point of water and examined whether the conversion efficiency is influenced or not by the phase state of reaction medium.…”