Theoretical studies on the catalytic hydrogenation of carbon dioxide by 3d transition metals single-atom catalyst supported on covalent triazine frameworks

The catalytic conversion of carbon dioxide (CO2) into value-added products is a significant emission reduction method. Among numerous catalysts, single-atom catalysts (SACs) show great potential in CO2 hydrogenation. However, it is difficult to predict the CO2 hydrogenation products because the SACs consisting of the same metal and different supports commonly show various catalytic selectivity. Here we study the catalytic mechanism of the CO2 hydrogenation process catalyzed by the SAC with 3d transition metals. The metal atoms are anchored on the covalent triazine frameworks (CTFs). We find the correlation between adsorption configuration and the selectivity of the CO2 hydrogenation. The coadsorption configuration of the H atom and CO2 molecule is favorable to forming the C-H bond in formate. A volcano relation based on activation barrier and 3d-orbital electron numbers was obtained. We found that the catalyst with Ni metal has the lowest activation barrier. We also explained the low catalytic activity of Sc, Ti, and V metals due to the inert intermediates occupying the active sites. This work may be helpful to design highly selective and highly active catalysts in CO2 hydrogenation.