Ab initio gas-phase bond energies of CNHx isomers and the reactivity and stability of aminomethylidyne (CNH2) on metal surfaces: UBI-QEP analysis

Energetics of reactions involving CNH2 as an intermediate on Fe, Ni, Pd, and Cu surfaces were determined with the unity bond index-quadratic exponential potential (UBI-QEP) method. The gas-phase bond energy parameters of CNHx isomers that are needed for the UBI-QEP treatment were obtained from high quality ab initio calculations. The results show that CN can dimerize to C2N2 on Pd and Cu, but the dimerization is difficult on Fe, and the polymerization of CNH2 is difficult. The N–H bond in CNH2 is more easily cleaved than the C–N bond, and CNH2 can be dissociated into CNH+H on Fe, Ni, Pd, and Cu surfaces, although it may remain on Pd and Cu metal surfaces due to CN and HCN hydrogenation. CNH2 hydrogenation leads to the formation of HCN, NH3, H2, and CH4 on those metal surfaces. The difficulty in breaking the C–N bond in CNHx isomers increases on the metal surfaces according to: Fe<Ni<Pd<Cu. The H-assisted C–N bond scission in some CNHx isomers on Fe, Ni, Pd, and Cu surfaces is discussed.