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Mechanism of Nitric Oxide Reduction by Hydrogen on Ni(110) and Ir/Ni(110): First Principles and Microkinetic Modeling

Wen, Hong, Huai, Li-yuan, Jin, Xin, Liu, Jing-yao
Journal of physical chemistry 2019 v.123 no.8 pp. 4825-4836
alloys, catalysts, density functional theory, dissociation, energy, hydrogen, models, nickel, nitric oxide, nitrogen, nitrous oxide, physical chemistry, temperature
The nitric oxide (NO) reduction by H₂ on the pure Ni(110) and single-atom Ir-doped Ni(110) (Ir/Ni(110)) surfaces are investigated by density functional theory calculations coupled with microkinetic modeling. The stability of the single-atom alloy (SAA) Ir/Ni(110) in vacuum and under real conditions is considered. The results show that NO dissociation is very facile on the clean and H-predosed Ni(110) surface, and the dissociated N atoms is more likely to couple with the surface-adsorbed NO to produce N₂O than with the N atom to form N₂. However, the energy barrier for N₂ formation is largely lowered by the doped Ir, whereas that for N₂O formation is greatly increased. Thus, N₂ is energetically preferentially formed on the Ir/Ni(110) surface. Microkinetic calculations further demonstrate that under ultrahigh-vacuum conditions, the selectivity toward N₂O is 100% below 420 K and that toward N₂ is over 80% above 460 K, in line with the experimental observation. In contrast, Ir/Ni(110) exhibits markedly improved selectivity toward N₂ in a wide temperature range (>90% at 320 K and 100% at T ≥ 340 K). The present work shows that the SAA Ir/Ni(110) catalyst is very effective in promoting the reduction of NO into N₂ while largely suppressing N₂O formation.