Li-Promotion in Rh-Based CO2 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.