Water-Enabled CO2 Hydrogenation to Ethanol via a Mixed-Potential-Driven Mechanism.

Ethanol synthesis from CO2 and H2 is currently a hot topic of research in heterogeneous catalysis. However, the underlying mechanism has not yet been clearly elucidated. We propose that the synthesis involves several other reactions on the electrode surface, as evident by the formation of a mixed potential. In this study, we prepared solid catalysts, Ru/CoOx and CuPd/C, as the nano-anode and nano-cathode components and carried out CO2 hydrogenation in the presence of small amounts of water to facilitate ion conduction. Ethanol was produced along with CO, CH4, and methanol at reaction temperatures below 473 K in the presence of both the catalysts. The activation energy for ethanol formation with Ru/CoOx was found to be 25 ± 5 kJ mol-1, which was much lower than those for the formations of CO (44 ± 4 kJ mol-1), CH4 (77 ± 7 kJ mol-1), and methanol (81 ± 9 kJ mol-1). In addition, the production of CO was promoted by the encapsulated water. These results also suggest a mixed-potential-driven mechanism for the synthesis of ethanol.