Mechanistic insight into catalytic oxidation of ammonia on clean, O- and OH-assisted Ir(111) surfaces

Periodic DFT calculations have been performed to systematically investigate the catalytic mechanisms of ammonia (NH₃) decomposition on clean, O- and OH-assisted Ir(111) surfaces. The adsorption configurations, reaction energies and barriers, and elementary steps were elaborated. Our results show that the NH_x (x = 1-3) decomposition prefers to proceed by means of the O- and OH-assisted reaction mechanisms, NH₃+O→NH₂+OH, NH₂+OH→NH+H₂O, and NH+OH→N+H₂O, rather than the direct NH_x decomposition of NH₃→NH₂→NH→N as a result of the high energy barriers involved. The promotion effect of the O- and OH-oxidizing agents are then discussed using energy barrier analysis. The relationships between the selectivity toward the final product and coverage, O to N coverage, and reaction temperature are elucidated. Finally, we compare our results with analogous investigations of NH₃ decomposition on Pt, Rh, and Ir surfaces. © 2013 WILEY-VCH Verlag GmbH & Co.