Oscillatory behaviour in the NO–H2 reaction over Ir(5 1 0)

The non-linear behaviour in the NO–H2 reaction over the stepped Ir(5 1 0) was studied using mass spectrometry, LEED and AES with NO pressures between 7.7×10−8 and 7.7×10−7 mbar and H2/NO ratios ranging from 1 to 54. In addition, TDS experiments were carried out to study the interaction between the species present on the surface during the reaction. During temperature programmed heating of a NO saturated surface in the presence of a hydrogen flow an explosive formation of N2, and to a lesser extent H2O, was observed, indicative of an autocatalytic reaction. Furthermore, TDS experiments on a NO saturated surface that was precovered with O, showed that the presence of Oads lowers the NO activation energy of desorption by 12 kJ mol−1. a heating–cooling cycle an adsorbate induced lifting of the surface reconstruction was observed under similar reaction conditions at which oscillations in rate were observed. The rates of N2 and H2O formation are in-phase during these oscillations. No other products were observed under oscillatory conditions. Possible mechanisms of the oscillations are discussed. Finally, a comparison between the non-linear behaviour over Ir(5 1 0), Pt(1 0 0) and other Ir and Rh surfaces was made.