Pattern Formation in a Surface Reaction with Global Coupling

Surface reactions exhibit unique features as model systems for nonlinear effects in chemical reactions. In addition they have an immense importance in heterogeneous catalysis in the chemical industry. Dynamic processes on surfaces, like the Pt — catalyzed CO-oxidation, can be described by a set of reaction-diffusion equations. For a certain range of reactants partial pressures and temperature of the sample, pattern formation like spiral waves, target patterns or solitary waves can be observed. When global coupling via the gas phase is introduced strong temporal oscillations may occur, sometimes exhibiting spatio-temporal patterns like standing waves, period doubling and chaotic behavior. The patterns mentioned were found under isothermal conditions. Of course, when increasing the reaction pressure, due to the exothermic nature of the CO-oxidation, temperature variations can be explored, observable with a sensitive InfraRed (IR) camera.