Mechanism of ammonia decomposition on clean and oxygen-covered Cu (1 1 1) surface: A DFT study

Highlights: • Dehydrogenation mechanism of NH₃ on clean and oxygen-covered Cu (1 1 1) was firstly studied using periodic DFT calculations. • The optimized structures and adsorption energies were obtained. • The results give the effect of using atomic oxygen to modify Cu (1 1 1) surface. • The energy barriers and reaction energies were calculated. • The existence of oxygen atom can reduce the energy barriers drastically and promote the decomposition of NH_x. - Abstract: Employing density functional theory (DFT), the adsorption and dehydrogenation mechanism of ammonia on clean and O-covered Cu (1 1 1) surfaces have been studied systematically. Different adsorption geometries were investigated for NH₃ and related intermediates. In addition, the stable co-adsorption configurations for the relevant co-adsorption groups were identified. The projected density of states (DOS) were calculated to understand the interaction between NH_x (x = 1, 3) species and Cu (1 1 1) surface and investigate the effect of oxygen atom on adsorption. Finally, transition states, energy barriers and reaction energies were determined to confirm the mechanism of dehydrogenation of NH₃ on clean and oxygen-covered Cu (1 1 1) surfaces. It was shown that NH is the most abundant intermediate on clean and O-covered Cu (1 1 1) surface due to the highest energy barrier, suggesting the dehydrogenation of NH group is the rate-determining step in the overall reaction. Furthermore, the existence of oxygen atom can reduce the energy barriers drastically and promote the decomposition of NH_x (x = 1–3), indicating that ammonia decomposition is more favorable on oxygen-covered Cu (1 1 1) surface