Ab initio gas-phase bond energies of CNH x isomers and the reactivity and stability of aminomethylidyne (CNH 2) on metal surfaces: UBI-QEP analysis

Abstract

Energetics of reactions involving CNH 2 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 CNH x 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 C 2N 2 on Pd and Cu, but the dimerization is difficult on Fe, and the polymerization of CNH 2 is difficult. The N–H bond in CNH 2 is more easily cleaved than the C–N bond, and CNH 2 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. CNH 2 hydrogenation leads to the formation of HCN, NH 3, H 2, and CH 4 on those metal surfaces. The difficulty in breaking the C–N bond in CNH x isomers increases on the metal surfaces according to: Fe<Ni<Pd<Cu. The H-assisted C–N bond scission in some CNH x isomers on Fe, Ni, Pd, and Cu surfaces is discussed.