Conversion of CO2 to CO is a potentially useful step in the desirable transformation of the greenhouse gas to fuels. We have shown that modification of FeTPP by introduction of phenolic groups considerably speeds up catalysis of this reaction.1 The prepositioned phenol groups incorporated into the catalyst molecule induce strong stabilization of the initial Fe0CO2 adduct through H-bonding. This positive factor is counterbalanced by the necessity to inject an additional electron to trigger catalysis. The prepositioned phenol groups thus play both the role of H-bonding stabilizers and high-concentration proton donors. They play the same role in the second electron transfer step which closes the catalytic loop concertedly with the breaking of one of the two C-O bonds of CO2 and with proton transfer.2 These results will be discussed in the framework of mechanism establishment for a rational benchmarking of molecular electrocatalysts for CO2 reduction.3 In this long quest for sophisticate design of transition metal complexes for the catalytic reduction of CO2, the report that a molecule as simple as protonated pyridine acts as a molecular catalyst for the conversion of CO2 to methanol aroused considerable interest.4 Still, understanding the mechanism requires a rational analysis of experimental facts: the reaction requires a platinum electrode. It will be shown that a detailed examination of the cyclic voltammmograms reveals that the reduction of pyH+ on a platinum electrode in the presence or absence of CO2 produces H2.5 Methanol could then result from hydrogen atoms adsorbed on platinum that could behave as hydrides in their reaction with CO2.6 However repeated tries of preparative-scale electrolysis show that no methanol is in fact produced. Possible reasons for experimental data discrepancies in the literature will be discussed. 1. Costentin, C.; Drouet, S.; Robert, M.; Savéant, J.-M. Science 2012, 338, 90-94. 2. Costentin, C.; Passard, G.; Robert, M.; Savéant, J.-M. J. Am. Chem. Soc. 2014, 136, 11821-11829. 3. Costentin, C.; Passard, G.; Robert, M.; Savéant, J.-M. PNAS 2014, 111, 14990-14993. 4. Cole, E. B.; Lakkaraju, P. S.; Rampulla, D. M.; Morris, A. J.; Abelev, E.; Bocarsly, A. B. J. Am. Chem. Soc. 2010, 132, 11539. 5. Costentin, C.; Canales, J. C.; Haddou, B.; Savéant, J.-M. J. Am. Chem. Soc. 2013, 135, 17671-17674. 6. Ertem, M. Z.; Konezny, S. J.; Araujo, C. M.; Batista, V. S. J. Phys. Chem. Lett. 2013, 4, 745-748.

Molecular electrocatalytic reduction of CO2 - mechanistic insights

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.