Spatiotemporal patterns during CO oxidation on Pt(100) at elevated pressures

CO oxidation an Pr(100) was investigated at reactant pressures of 8 Pa usin g ellip-somicroscopy for surface imaging to monitor spatiotemporal pattern formation on the catalyst surface and mass spectroscopy to monitor the inte gral reaction rate Three distinct temperature regions showing nonlinear phe nomena were found. The first region, at 540 - 615 K, is characterized by ma croscopic, regular reaction-rate oscillations with spatially uniform, insta ntaneous transitions between CO and oxygen covered states. Regular; periodi c oscillations were nor observed on Pt(100) before. The second region, 480- 540 K exhibited continuous dynamic pattern formation with no visible macros copic kinetic oscillations Front speeds measured indicated a decrease in ox ygen front velocity and an increase in CO front velocity with an increasing GO/O-2 partial pressure ratio. The third region, 390 - 430 K, is character ized by macroscopic rate oscillations, which continued for several oscillat ion periods and then ceased with the onset of pattern formulation.