KINETIC PHASE-DIAGRAM FOR CO OXIDATION ON PT(210) - PATTERN-FORMATIONIN THE HYSTERESIS AND OSCILLATION REGIONS

The reactive behavior of catalytic CO oxidation on Pt(210) is studied by means of combined reaction rate measurements and photoelectron emis sion microscopy (PEEM). These methods allow an investigation of the ph enomena at macroscopic and mesoscopic level, respectively. The externa l control parameters (how rate, CO and oxygen partial pressures, surfa ce temperature and scanning rates of pressure and temperature) are sys tematically varied to reveal various reactive regions in parameter spa ce. The macroscopic measurements for a given temperature and flow rate (under isothermal conditions) show that lower pressures lead to a pro nounced clockwise hysteresis in the production rate of CO2, while incr easing pressures' cause a systematic narrowing leading to a crossing: of the two hysteresis branches into a region of counterclockwise hyste resis. A further pressure increase leads to macroscopic temporal oscil lations. Mesoscopic spatiotemporal oscillations appear at the same con ditions. The resulting macroscopic isothermal kinetic phase diagram ex hibits a cross-shaped characteristic similar to that previously obtain ed for the Pd(110) surface. The mesoscopic lateral distribution of CO and oxygen adsorbed on the surface is monitored with the photoelectron emission microscope during the reaction at isothermal conditions and different constant oxygen pressures. The observed mesoscopic spatiotem poral patterns, such as islands, waves, target patterns and spirals, a re correlated via the external control parameters with different regio ns in the macroscopic isothermal phase diagram. The results are compar ed with previous data of CO oxidation on other surfaces, like Pd(110) and Pt(110). (C) 1997 American Institute of Physics.