Decomposition mechanism of methylamine to hydrogen cyanide on Pt(111): selectivity of the C–H, N–H and C–N bond scissions

Periodic density functional theory (DFT) calculations were performed to systematically investigate the decomposition mechanism of methylamine (CH3NH2) to hydrogen cyanide (HCN) on Pt(111). The geometries and energies for all species involved are analyzed, and the decomposition network is mapped out to elaborate the reaction mechanism. Our results show that the CH3NH2, methanimine (CH2NH) and HCN prefer to desorb, while the other species prefer to decompose; the decomposition pathway prefers the successive N-H bond scissions followed by the C-H bond scissions, that is, CH3NH2 -> CH3NH -> CH3N -> CH2N -> HCN. The electronic structure and energy barrier analysis are used to identify the initial competitive scissions of C-H, N-H and C-N bonds. The interaction between fragments and surface in the TS plays a decisive role in controlling the energy barrier of initial CH3NH2 decomposition on Pt(111). Finally, the Bronsted-Evans-Polanyi (BEP) relation identifies that the C-H and N-H bond scissions stay competitive, but the C-N bond scission is not facile to occur.