The surface chemistry of NOx on metal oxides is important to environmental catalysis. Here we employ plane-wave, supercell DFT calculations to characterize NOx chemistry at the RuO2(1 1 0) surface as a model of a catalytically active transition metal oxide surface. We identify a range of potential NOx intermediates, and use a thermodynamic analysis to characterize their stability as a function of gas exposure conditions. Adsorbed NO (nitrosyl) and to a lesser extent NO3 (nitrate) dominate the surface phase diagram. Computed vibrational spectra are in good agreement with observation and provide new assignments of observed surface species. NO2 is thermodynamically unstable at the surface and its desorption is never favored: in contrast to its activity towards CO oxidation, RuO2(1 1 0) is not an effective NO oxidation catalyst. Rather, it could be effective as a reversible NO adsorber. Finally, we characterize the kinetics of several NO surface reactions and identify a pathway that may contribute to the decomposition of NO to N-2 and N2O over partially reduced surfaces. (c) 2010 Elsevier B.V. All rights reserved.