Direct C–C Coupling of CO2 and the Methyl Group from CH4 Activation through Facile Insertion of CO2 into Zn–CH3 σ‑Bond

Conversion of CO2 and CH4 to value-added products will contribute to alleviating the green-house gas effect but is a challenge both scientifically and practically. Stabilization of the methyl group through CH4 activation and facile CO2 insertion ensure the realization of C–C coupling. In the present study, we demonstrate the ready C–C coupling reaction on a Zn-doped ceria catalyst. The detailed mechanism of this direct C–C coupling reaction was examined based on the results from density functional theory calculations. The results show that the Zn dopant stabilizes the methyl group by forming a Zn–C bond, thus hindering subsequent dehydrogenation of CH4. CO2 can be inserted into the Zn–C bond in an activated bent configuration, with the transition state in the form of a three-centered Zn–C–C moiety and an activation barrier of 0.51 eV. The C–C coupling reaction resulted in the acetate species, which could desorb as acetic acid by combining with a surface proton. The formation of acetic acid from CO2 and CH4 is a reaction with 100% atom economy, and the implementation of the reaction on a heterogeneous catalyst is of great importance to the utilization of the greenhouse gases. We tested other possible dopants including Al, Ga, Cd, In, and Ni and found a positive correlation between the activation barrier of C–C coupling and the electronegativity of the dopant, although C–H bond activation is likely the dominant reaction on the Ni-doped ceria catalyst.