Carbon neutral energy cycles necessitate the conversion of CO2
into other compounds.1
However, the unfavorable thermodynamics and slow kinetics of multiple proton and electron transfers makes CO2
conversion difficult. Improved insight into these processes would help elucidate reaction mechanisms that guide the development of improved and versatile photo- and electro-catalysts.2
Recent experiments have demonstrated that inorganic Ru complexes can catalyze the photo- and electro-chemical reduction of CO2 into methanol.3
These reactions involve aqueous phase aromatic N-heterocycles (ANH) in addition to complexes that contain ANH ligands themselves (e.g. phenanthroline). We previously developed4
a set of thermodynamic descriptors from quantum chemistry calculations to describe electrochemical conditions at which ANH molecules participate in energetically efficient proton and electron transfers. In this study, we report our latest efforts to provide insight into the mechanism of Ru catalyzed CO2 reduction using Pourbaix diagram descriptors. Although transition metal complexes are normally assumed to be electrochemically stable, our calculations indicate that certain environments may result in hydride transfers facilitated via the ligands of the inorganic complexes.
1. Olah, G. A., Prakash, G. K. S. & Goeppert, A. Anthropogenic Chemical Carbon Cycle for a Sustainable Future. J. Am. Chem. Soc. 133, 12881–12898 (2011).
2. Qiao, J., Liu, Y., Hong, F. & Zhang, J. A review of catalysts for the electroreduction of carbon dioxide to produce low-carbon fuels. Chem. Soc. Rev. 43, 631–675 (2013).
3. Boston, D. J., Pachón, Y. M. F., Lezna, R. O., de Tacconi, N. R. & MacDonnell, F. M. Electrocatalytic and Photocatalytic Conversion of CO2 to Methanol using Ruthenium Complexes with Internal Pyridyl Cocatalysts. Inorg. Chem. 53, 6544–6553 (2014).
4. Marjolin, A. & Keith, J. A. Thermodynamic Descriptors for Molecules That Catalyze Efficient CO2 Electroreductions. ACS Catal. 5, 1123–1130 (2015).