Reactors, Kinetics, and Catalysis

( ) CO oxidation on Pt 100 was in®estigated at reactant pressures of 8 Pa using ellipsomicroscopy for surface imaging to monitor spatiotemporal pattern formation on the catalyst surface and mass spectroscopy to monitor the integral reaction rate. Three distinct temperature regions showing nonlinear phenomena were found. The first region, at 540 ] 615 K, is characterized by macroscopic, regular reaction-rate oscillations with spatially uniform, instantaneous transitions between CO and oxygen co®ered states. Regu( ) lar, periodic oscillations were not obser®ed on Pt 100 before. The second region, 480 ] 540 K, exhibited continuous dynamic pattern formation with no ®isible macroscopic kinetic oscillations. Front speeds measured indicated a decrease in oxygen front ®elocity and an increase in CO front ®elocity with an increasing COrO partial pressure 2 ratio. The third region, 390 ] 430 K, is characterized by macroscopic rate oscillations, which continued for se®eral oscillation periods and then ceased with the onset of pattern formation.