High-pressure reduction of carbon dioxide in reactive liquid mixtures

Density-functional theory based molecular-dynamics simulations were used to investigate high-pressure chemical reactions in liquid mixtures of ${\mathrm{CO}}_{2}$ with several elements (Si, Mn, and Fe) at high temperatures of 2000--3000 K. Our ab initio simulations indicate that these reactant elements can reduce ${\mathrm{CO}}_{2}$ to C at high pressures (20 GPa) leading to the formation of C-C chains, with Si by far the most effective carbon-reducing agent. A combined chemical analysis using Bader charge analysis and crystal orbital Hamilton population (COHP) on simulation snapshots shows that significant charge transfer from the reducing element to the C atoms creates instability in the C-O covalent bonds. COHP analysis further shows that Mn/Fe-O and Mn/Fe-C bonding interactions are weaker compared to the Si counterparts. These results further our understanding of the redox chemistry of ${\mathrm{CO}}_{2}$ at conditions relevant to planetary mantle interiors and demonstrate the effectiveness of high pressure in the reduction of ${\mathrm{CO}}_{2}$ directly to solid carbon.