High-yield reduction of carbon dioxide into formic acid by zero-valent metal/metal oxideredox cycles

Abstract

A strategy for reduction of CO₂ is described that produces formic acid from CO₂ (ca. 80% formic acid yield) via the oxidation of a zero-valent metal under hydrothermal conditions. The oxidized metal can be regenerated using glycerin, which produces lactic acid. Hydrogen production is demonstrated through metal oxidation in the presence of CO₂ with zero-valent Fe, Mn, Zn, and Al metals under hydrothermal conditions, where it is found that a maximum hydrogen formation yield of ca. 99.4% was achieved. The metals, once oxidized, could be readily reduced (ca. 100% for Fe) to their zero-valent state by contact with glycerin. The results demonstrate that a carbon cycle can be driven by the oxidation and reduction of commonly available metals.