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

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.