Water-Gas Shift Reaction in Deep Earth

The deep carbon cycle plays a critical role in the sustainable development of life. The change in the oxygen fugacity in Earth’s interior leads to stabilization of carbon with different oxidation states, from diamond and methane in the deep Earth to CO₂ and carbonate minerals near Earth’s surface. In the industrial water-gas shift reaction, CO is oxidized to CO₂ in the presence of water, during which formic acid is considered a short-lived intermediate. Using extensive ab initio molecular dynamics simulations, we found that at the high pressure (P) and high temperature (T) conditions as found in the deep Earth, CO reacts with water to generate formic acid as a product. We also calculated the free energy of formic acid, and predicted the possible P-T range of the existence of formic acid when carbon is not fully oxidized. Our findings have important implications for the formation of diamonds and hydrocarbon reactions inside Earth.