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Density-functional theory based molecular-dynamics simulations were used to investigate high-pressure chemical reactions in liquid mixtures of CO2 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 CO2 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 CO2 at conditions relevant to planetary mantle interiors and demonstrate the effectiveness of high pressure in the reduction of CO2 directly to solid carbon.