Theoretical Study on the Electroreduction of CO2 to α-Olefins by Tandem Catalysis of Polymetallic Phthalocyanine Two-Dimensional Carbon-Rich Conjugated Frameworks (CCFs)

Abstract

In the carbon dioxide reduction reaction (CO₂RR), the direct synthesis of unsaturated heavy hydrocarbons such as α-olefins is more attractive for modern society. However, the underlying reaction mechanism remains unclear because the C–C coupling towards α-olefins is difficult to control. Therefore, in order to improve the selectivity of α-olefins, a tandem catalyst is proposed based on CCFs. After detailed screening and analysis, Fe-Ti-Pc-Mo-S-CCFs composed of Fe-Ti-Pc ligand and MoS₄ node is considered to have high selectivity for CO₂RR and good inhibition of competitive HER, which is attributed to the orbital hybridization mechanism between CO₂ and Fe and Ti. The reaction mechanism and complex intermediates of the synthesis of α-olefins from the CO₂ hydrogenation reaction are systematically investigated, including four pathways. Density functional theory (DFT) simulations indicate that the asymmetric coupling of *CH₂ and *COOH forms *CH₂COOH, followed by the continuous insertion of CH₂, leading to the formation of α-olefins. This mechanism is the optimal pathway for CO₂RR. In addition, the competitiveness of C–C coupling and proton-coupled electron transfer (PCET) reactions are also discussed. The results conclude that C₁-C₂ and C₁-C₃ couplings are more advantageous. In this work, the results reveal that Fe-Ti-Pc-Mo-S-CCFs has the stability, high selectivity, and high conductivity, enables CO₂ reduction to a high-value product, and provides a novel possibility for the design of electrocatalysts for CO₂RR.

Graphical Abstract