Adsorption and dissociation of NO on Ir(100): A first-principles study

Abstract

Density functional theory (DFT) and periodic slab model have been used to systemically study the adsorption and dissociation of NO and the formation of N2 on the Ir(100) surface. The results show that NO prefers the bridge site with the N-end down and NO bond-axis perpendicular to the Ir surface, and adsorption to the top site is only 0.05 eV less favorable, whereas the hollow adsorption is the least stable. Two dissociation pathways for the adsorbed NO on bridge or top site are located: One is a direct decomposition of NO and the other is diffusion of NO from the initial state to the hollow site followed by dissociation into N and O atoms. The latter pathway is more favorable than the former one due to the lower energy barrier and is the primary pathway for NO dissociation. Based on the DFT results, microkinetic analysis suggests that the recombination of two N adatoms on the di-bridge sites is the predominant pathway for N2 formation, whereas the formation of N 2O or NO2 is unlikely to occur during NO reduction. The high selectivity of Ir(100) toward N2 is in good agreement with the experimental observations. © 2011 American Institute of Physics.