Reduction of CO2 to CO by an Iron Porphyrin Catalyst in the Presence of Oxygen

TLDR: In this article, an iron porphyrin complex with four ferrocene groups in its distal site is demonstrated to reduce CO2 unabated in the presence of O2 as it can reduce O2 to benign H2O under the same conditions.

Abstract: Reduction of CO2 to value-added chemicals is a logical way of fixing the rising levels of CO2. Activation and reduction of CO2 requires low-valent transition metals as catalysts. A major challenge in this chemistry is sensitivity of these low-valent metal sites to more abundant O2. Since O2 is a stronger oxidant than CO2 and isolated from the obvious competitive inhibition of CO2, partial reduction of O2 leads to formation of reactive oxygen species like O2– and H2O2, which are deleterious to the catalyst itself. An iron porphyrin complex appended with four ferrocene groups in its distal site is demonstrated to reduce CO2 unabated in the presence of O2 as it can reduce O2 to benign H2O under the same conditions. Further investigations reveal that iron porphyrins, in general, reduce CO2 selectively in the presence of O2. The aforementioned selectivity is derived from a 500 times faster rate of reaction of CO2 with Fe(0) porphyrin relative to O2 despite a higher driving force for the latter.