DFT Study on the CO 2 Reduction to C 2 Chemicals Catalyzed by Fe and Co Clusters Supported on N-Doped Carbon.

The catalytic conversion of CO 2 to C 2 products through the CO 2 reduction reaction (CO 2 RR) offers the possibility of preparing carbon-based fuels and valuable chemicals in a sustainable way. Herein, various Fe n and Co 5 clusters are designed to screen out the good catalysts with reasonable stability, as well as high activity and selectivity for either C 2 H 4 or CH 3 CH 2 OH generation through density functional theory (DFT) calculations. The binding energy and cohesive energy calculations show that both Fe 5 and Co 5 clusters can adsorb stably on the N-doped carbon (NC) with one metal atom anchored at the center of the defected hole via a classical MN 4 structure. The proposed reaction pathway demonstrates that the Fe 5 -NC cluster has better activity than Co 5 -NC, since the carbon-carbon coupling reaction is the potential determining step (PDS), and the free energy change is 0.22 eV lower in the Fe 5 -NC cluster than that in Co 5 -NC. However, Co 5 -NC shows a better selectivity towards C 2 H 4 since the hydrogenation of CH 2 CHO to CH 3 CHO becomes the PDS, and the free energy change is 1.08 eV, which is 0.07 eV higher than that in the C-C coupling step. The larger discrepancy of d band center and density of states (DOS) between the topmost Fe and sub-layer Fe may account for the lower free energy change in the C-C coupling reaction. Our theoretical insights propose an explicit indication for designing new catalysts based on the transition metal (TM) clusters supported on N-doped carbon for multi-hydrocarbon synthesis through systematically analyzing the stability of the metal clusters, the electronic structure of the critical intermediates and the energy profiles during the CO 2 RR.