Spatio-temporal dynamics of oscillatory heterogeneous catalysis: CO oxidation on platinum

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Abstract
Reaction-rate oscillations in the oxidation of carbon monoxide on the surface of platinum catalysts are studied in a continuous flow reactor at atmospheric pressure using infrared imaging. Small-amplitude temperature oscillations (0.2–8 K) result in approximately isothermal conditions, where changes in rate constants, for typical activation energies and temperatures, are small. The catalysts are in the form of platinum thin films on quartz substrates and provide highly repeatable oscillatory behavior. The platinum films are fabricated in the form of annular rings which provide a quasi-one-dimensional geometry in order to simplify comparison to theoretical models. Time-series measurements by means of thermocouples are used to characterize the oscillations. The infrared images show that most oscillations are spatially synchronized to within the 0.25 s time resolution of the experiment. The images also show that ‘‘fine structure’’ oscillations (i.e., small-amplitude, high frequency oscillations superimposed on larger-amplitude waveforms) are associated with spatially desynchronized patterns.