Li-Promotion in Rh-Based CO ₂ Hydrogenation Catalysts to Ethanol: Enabling Carbon–Carbon Bond Formation at the Interface

Higher alcohol synthesis from syngas (CO/H₂) has attracted large research efforts in the past decades. However, the analogous reaction using CO₂ as a feedstock remains relatively underexplored. Due to the net reduction in anthropogenic CO₂ emissions that can be achieved by this approach (provided green H₂ is used), ethanol synthesis from CO₂ has become a highly desirable reaction. Nevertheless, highly active and selective catalysts for this reaction have remained elusive and poorly understood, and their development presents a formidable task. By leveraging the synthesis of a well-defined, silica-supported Rh-Li based catalyst, we have improved our understanding of the role of lithium in the formation of ethanol from CO₂. Using state-of-the-art spectroscopy, such as X-ray absorption spectroscopy, probe molecule infrared spectroscopy, and in-situ diffuse reflectance infrared spectroscopy, we were able to evidence the presence of an activated CO species at the interface of metallic Rh and Li⁺ which readily allows the insertion of -CHx species in the RhLi@SiO₂ system. Complementary computational studies indicate that the insertion of CHx into CO is drastically facilitated and that the presence of Li⁺ protects -CHx species from overhydrogenation.