Kinetic phase transitions in the reaction CO+O→CO2 on Ir(111) surfaces

The oxidation of CO on Ir(111) surfaces was investigated under UHV conditions in the temperature range 360 K to 700 K by CO2 rate measurements utilizing mass spectroscopy. Steady-state CO2 rates were measured at constant total CO+O2 gas flux and variable gas composition (YCO=Y, YO2=1−Y) using mass flow controllers which allowed changes in the CO/O2 gas composition down to 0.1%. Between 360 K and 450 K the CO2 rates initially increase proportional to Y (T<400 K) or to Y1.5 (420 K