Density functional theory study of nickel and copper single-atom catalysts on graphitic carbon nitride for benzene to phenol oxidation.

During the present study, single-atom catalysts (SACs) were designed by decorating graphitic carbon nitride with copper (I) and nickel (I) ions. The designed catalysts were employed for studying the possible reaction pathways for benzene to phenol oxidation. The calculations were carried out using the density functional theory (DFT) method at the M06-2X/def2-SVP level of theory. To select the catalyst among various spin multiplicities and decoration places, the relative energies, interaction energies, and energy gaps were compared, which showed the smaller spin multiplicity and center position of the decorated metal was the most suitable case for both SACs. To investigate the reaction process, two possible routes were considered and the relative energies and Gibbs free energies of all involved species in these pathways were calculated in the gas phase. The gas phase energies confirmed the reliability of the proposed routes and the higher ability of Ni-based SAC than Cu-based SAC by both thermodynamic and kinetic data. To consider the solvent effects, the polarizable continuum model(PCM) was employed using acetonitrile and methanol as two common solvents. The obtained energy values in solvents confirmed the higher potency of Ni SAC versus Cu SAC for this reaction and both solvents showed nearly similar overall barriers and thermodynamic values.