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

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.