Insights into the relationship between the CO activation over single-atom catalysts and the unpaired d-electronic number of doped transition metal

In order to characterize the relationship between the unpaired d-electronic number (nud) of doped transition metal and catalytic ability, CO dissociation pathway over the single-atom catalysts, graphene and N-modified graphene decorated with 3d- and 4d- transition metal, have been discussed by the density functional theory (DFT) method. It is indicated that single-atom catalysts decorated with ⅥB or ⅦB subgroup transition metal are more active than others for CO activation. From IIIB toⅠB subgroup, the activation barrier shows a clear trend of first decreasing and then increasing. Based on the d-electronic orbital arrangement of transition metal, it can be inferred that the greater the nud value of doped transition metal, the higher the catalytic ability of single-atom catalysts. Moreover, the C = O bond length when CO adsorbed on single-atom catalysts confirm this result. Meanwhile, compared with TM-C3 catalysts, N-modification can improve catalytic ability of single-atom catalysts, and the Mo-N3 catalysts is the best candidate for CO activation. Moreover, the modest d-band center (εd) and electron-enriching coordination environment are advantageous to improving the catalytic performance of single-atom catalysts. It offers theoretical guidance for the further research and design of single-atom catalysts.