Photocatalytic Reduction of CO₂ to CO and Formate: Do Reaction Conditions or Ruthenium Catalysts Control Product Selectivity?

Abstract

The photocatalytic reduction of CO2 can generate a number of products with CO and HCO2 – being two of the most commonly observed. Frequently, the selective formation of one of these products is presumed to be the result of catalyst design. However, several common variables are present when exploring the photocatalytic CO2 reduction reaction. In order to better understand the origin of selectivity in this reaction, the choices of solvent, electron and proton source, photosensitizer (PS), and catalyst were evaluated in photocatalytic CO2 reduction reactions. Intriguingly, highly selective catalysts for CO or HCO2 – under one set of conditions can be transformed by these environmental choices into becoming highly selective for the opposite product while retaining high turnover numbers. This highlights the importance of carefully considering reaction conditions before ascribing catalyst selectivity to an inherent molecular design property.

Ancillary Ligand Effects on Heteroleptic IrIII Dye in Dye‐Sensitized Photocatalytic CO2 Reduction: Photoaccumulation of Charges on Arylated Bipyridine Ligand and Its Control on Catalytic Performance

“… Photo‐labilization of the bipyridyl ligand from one‐electron reduced species of [Ru(bpy) 3 ] 2+ [67–72] …”

“…Figure 10 shows that two Ru II -sensitized systemsw ere found to exhibit the relativelyl ower conversion activities than those of the IrPSs-based catalytic systems with their early leveling-off behavior at~3h.T he low performance is most likelyt ob e caused by much lower product selectivity by the formate (HCOO À )p roduction from [Ru(N^N) 2 (solvent) 2 ]s peciesw hich is generated from photodissociation of one N^N ligand via d-d state. As observed in lots of Ru II -sensitized CO 2 reduction (Figures 10 and 12), [65][66][67][68][69][70] the production of HCOO À catalyzed by [Ru(N^N) 2 (solvent) 2 ]s pecies is terminated earlier with its low structural stability,l owering the overall photocatalytic activities with the resulting low product selectivity.T his comparison reflects that the Ir III photosensitizers works as am ore suitable photosensitizer than do Ru II -based photosensitizers.…”

Impact of the Dissolved Anion on the Electrocatalytic Reduction of CO2 to CO with Ruthenium CNC Pincer Complexes

“…Quantitation of CO and CH 4 were made using an FID detector, while H 2 was quantified using a TCD detector. The CPE reactions were analyzed for formate as previously described and no appreciable amount was observed . In these studies, CO and H 2 were the only two appreciable products detected.…”

“…The study of ruthenium‐based molecular catalysts driving the CRR reaction remains an intense and attractive area of research . Recent studies on the photocatalytic CRR with [Ru II (bpy) 2 (CO) 2 ][PF 6 ] 2 ( Ru‐1 ) and a pyridinol‐derived pincer ligated ruthenium chloride complex ( Ru‐2 ) have revealed higher rates of reactivity and a higher durability of the pincer complex . Additionally, electrocatalysis appeared to be faster with Ru‐2 and halide‐free Ru‐3 (vs. Ru‐1 ) via preliminary cyclic voltammetry (CV) analysis .…”

Photocatalytic CO2 Reduction under Visible‐Light Irradiation by Ruthenium CNC Pincer Complexes

“…A similar CNC ruthenium complex, [(CNC OMe )RuCl(NCMe) 2 ]OTf, in which a 4‐methoxy group is introduced to the pyridyl moiety in CNC ligand, has been reported . The use of this complex for the photocatalytic CO 2 reduction in CH 3 CN with photosensitizer [Ir(ppy) 3 ] resulted in selective production of CO (TON CO =227; selectivity 97 %), but in DMF with photosensitizer [Ru(bpy) 3 ] 2+ production of formate was dominant (TON HCOOH =143; selectivity 90 %).…”