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

- 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 NHx.

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 NHx (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 NHx (x = 1-3), indicating that ammonia decomposition is more favorable on oxygen-covered Cu (1 1 1) surface.