Density functional theory (DFT) calculations are used to investigate the adsorption of nitrogen oxides (NOx) (x = 1,2) and oxidation reaction on Ir (1 0 0) surface. On clean surface, NO molecule energetically prefers to bond at bridge sites for all studied coverages (Theta = 0.25, 0.50, 0.75 and 1.00) monolayer (ML). An electron donation from the occupied orbitals to the d metal band and a back donation from the substrate to the 2 pi* orbital occur for adsorbed NO on Ir (1 0 0) surface, which causes an increase in N-O bond. NO2 molecule exhibits a variety of adsorption geometries; the most energetically favorable is the mu-N,O-nitrito configuration with an adsorption energy 1.91 eV. The reaction pathway and the transition state (TS) are determined using constrained minimization method. At the TS, the adsorbed oxygen (O-a) atom and NO molecule diffuse to less stable states (top). Then they react to form chemisorbed NO2 with activation energy about 1.41 eV. (C) 2012 Elsevier B.V. All rights reserved.