Adsorption state of NO on Ir(111) surfaces under excess O2 coexisting condition

Iridium (Ir) exhibits a good efficiency for reduction of NO under excess O-2 coexisting conditions at temperatures higher than 250 degrees C. On the other hand, the advantage is lost at lower temperatures below 250 degrees C under O-2 existence, compared to any other platinum group metals. In this study, adsorption behavior of NO on Ir(111) single-crystal surfaces under excess O-2 coexisting conditions at the temperatures from room temperature to 250 degrees C has been studied by in-situ X-ray Photoelectron Spectroscopy (XPS). It is revealed that the coexisting O-2 induces formation of a high-density chemisorbed atomic oxygen (O) phase and the atomic O phase suppresses adsorption of NO at on-top sites significantly, which suggests that the suppression of NO adsorption causes a decrease in the ability of NO reduction at the lower temperatures.