The effect of coordination states of cobalt on Co-Nx co-doped graphene for selective oxidation of H2S: A DFT study

The transition metal coordinated with nitrogen atoms doped carbon catalysts shows great potential on H2S selective oxidation into elemental sulfur. Herein, we conducted CoN3 and CoN4 co-doped graphene as model materials to elucidate the regulating effect of coordination environment of Co atom on the catalytic performance by Density Functional Theory (DFT) methods. The adsorption behavior, dissociation, oxidation by atomic O and O2 have been studied in detail. The CoN3 doped graphene (PG-Co-N3) exhibits stronger affinity towards both H2S and O2 molecules with adsorption energy of −0.774 eV and −2.385 eV than CoN4 doped graphene (PG-Co-N4) (−0.426 eV, −0.690 eV). Among three possible reaction routes, the oxidation by atomic O is the most favorable reaction pathway on both PG-Co-N3 and PG-Co-N4 surfaces. In other two routes, H2S dissociation with or without O2 assisting on PG-Co-N3 demonstrates lower reaction energy barrier of the rate determining steps than on PG-Co-N4. These results could provide a new strategy to design novel catalysts for H2S selective oxidation, and reveal the effect of coordination environment of transition metal and nitrogen co-doped graphene on the mechanism of oxidation process.