The mechanism of ammonia decomposition and oxidation on Ir(110) was studied on the basis of periodic density functional theory calculations and microkinetic modeling. The results indicate that NH3dissociation is more favorable than desorption at atop site, while at top site NH3desorption and dissociation are competitive. On the other hand, when O or OH is co-adsorbed, the NH3 dehydrogenation is slightly inhibited and mainly via hydrogen abstraction reaction rather than thermal decomposition, while it is reversed for NH2 dehydrogenation. The former mechanism is favored for O assisted NH dehydrogenation, while it changed to latter one for OH. On clean Ir(110), N + NH → N2 + H pathway is the major N2 formation pathway and N + N is also involved but less competitive, while N + N becomes the predominant one and is enhanced on O-predosed Ir(110). NO formation occurs only at higher temperature when N2 is desorbed from the surface. The microkinetic analysis further confirms that the dominant product is N2 at low temperature while becomes NO as temperature increases, and the temperature of NO formation decreases when O2 partial pressure increases. The present calculation results are in good agreement with the experimental observations.
Received 11 December 2012Accepted 18 March 2013Published online 08 April 2013
This work is supported by the National Natural Science Foundation of China (NNSFC) (20973077 and 20303007) and the Program for New Century Excellent Talents in University (NCET).
Article outline: I. INTRODUCTION II. COMPUTATIONAL DETAILS III. RESULTS AND DISCUSSION A. Stepwise dehydrogenation pathways 1. Pathways on clean Ir(110) 2. Effect of predosed oxygen 3. Effect of predosed hydroxyl B. Formation of products 1. N2 formation 2. NO and N2O formation 3. H2 and H2O formation 4. Effect of predosed O on N2 and NO formation C. Understanding possible product selectivity IV. CONCLUSIONS
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48.See supplementary material at http://dx.doi.org/10.1063/1.4798970 for a description of the microkinetic model including the rate constant calculations for ten elementary steps and the coverage expressions of the surface species obtained from steady-state approximation. [Supplementary Material]