Energetics of C–N coupling reactions on Pt(111) and Ni(111) surfaces from application of density-functional theory

Abstract

We applied density-functional theory (DFT) with the projector-augmented-wave method (PAW) to investigate systematically the energetics of C–N coupling reactions on Pt(111) and Ni(111)surfaces. Our approach includes several steps: the adsorption of reactants and products (CH_x, NH_y and CH_xNH_y, x = 0–3, y = 0–2), movement of molecular fragments on the surface, and then C–N coupling. According to our calculations, the energies (ignoring the conventional negative sign) of adsorption of CH_x and NH_y on Pt(111)/Ni(111) surfaces decrease in the order C > CH > CH₂ > CH₃ and N > NH > NH₂, with values 7.41/6.91, 6.97/6.52, 4.58/4.39, 2.19/2.01 eV and 5.10/5.49, 4.12/4.79, 2.75/2.87 eV, respectively. Regarding the adsorption energies among CH_xNH_y, the adsorption energy of CNH₂ species is the highest on the Pt(111) surface, whereas on the Ni(111) surface CH₃N is the most stable. The C–N coupling barriers differ on the two metallic surfaces despite the structures of initial, transition and final states being similar. On the Pt(111) surface, the coupling reaction of CH₂ + NH₂ has the smallest barrier, whereas CH + NH₂ is the most favorable on the Ni(111) surface. The detailed local density of states (LDOS) and electron-localization functions (ELF) were investigated to rationalize the calculated outcomes.