SPATIAL PATTERN-FORMATION IN THE CATALYTIC NO + CO REACTION ON A CYLINDRICAL PT SINGLE-CRYSTAL

Spatial pattern formation in the NO + CO reaction on a cylindrical Pt single crystal with [001] axis has been investigated in the 10(-6) Torr range between 400 and 430 K under conditions where a Pt(100) crystal exhibits oscillatory behaviour. The investigations were conducted using photoemission electron microscopy (PEEM) as an in-situ method to image the lateral adsorbate distribution during the reaction with a resolution of approximately 1-mu-m. Only the orientational range between (100) and (310) on the cylinder was found to be active in NO dissociation and hence in the surface reaction. In this active zone one finds propagating reaction fronts and more complex spatiotemporal patterns. Under stationary conditions the spatial patterns display turbulent behaviour, while upon a small temperature change of 1-3 K the turbulent patterns order into a target pattern. Macroscopically, this transition corresponds to the excitation of kinetic oscillations which then decay after a few cycles as the pattern becomes turbulent again. These observations can be explained as being due to a lack of a long-range synchronization via gas-phase coupling in this reaction system.