Sustainable Carbon Dioxide Valorization Through Catalytic and Non-Catalytic Routes: A DFT Study

This study presents a comprehensive thermodynamic evaluation of several CO2 conversion pathways, both non-catalytic and catalyst-assisted, using density functional theory (DFT) calculations in Gaussian 16 (B3LYP/6-311++G(d,p)). In the non-catalyzed section, three key routes are examined: hydrogenation (CO2 + H2 → CO + H2O), dry methane reforming, and the reverse water–gas shift (RWGS). For the hydrogenation reaction, the Gibbs free energy change (ΔG) decreases from +0.018 to +0.005 Hartree as the temperature increases from 298.15 K to 1173.15 K, indicating a slight improvement in feasibility but still a high activation barrier of 0.326 Hartree, underscoring the need for catalysis. Dry methane reforming is both exothermic and spontaneous, with ΔG ≈ = −0.049 Hartree at 298.15 K and −0.030 Hartree at 593.15 K; however, operating under harsh conditions may accelerate degradation of reactor materials. In the catalyst-assisted section, copper surfaces and Cu3M clusters (M = Sc, V, Ni, Cu, Co and Fe) are evaluated alongside two bimetallic catalysts, Fe2 and Ni2, under electrochemical CO2 reduction (eCO2RR) conditions. Scandium- and vanadium-doped clusters exhibit significant CO2 adsorption, as evidenced by shifted vibrational frequencies between 800 and 1800 cm−1 that signal C=O bond weakening. Under the evaluated thermobarometric conditions, Ni2-containing systems displayed lower Gibbs energy values within their own optimized intermediate set and higher entropy values than the corresponding Fe2-containing set, suggesting greater configurational flexibility and favorable stabilization trends. However, because Fe2 and Ni2 systems are chemically different, absolute total energies were not used as a standalone criterion for intrinsic catalytic superiority. Overall, while some non-catalytic routes become thermodynamically more favorable only at high temperature, the explicit inclusion of catalytic models, particularly doped Cu3M clusters and Ni-containing systems, indicates enhanced CO2 activation through stronger catalyst–adsorbate interactions, vibrational weakening of C=O bonds, and favorable electronic descriptors. These results suggest that catalytic systems may enable CO2 conversion under milder conditions, although full kinetic confirmation requires comparative transition state calculations for each elementary catalytic step.