SPATIOTEMPORAL PATTERN-FORMATION ON POLYCRYSTALLINE PLATINUM SURFACES DURING CATALYTIC CO OXIDATION

The individual grains of a polycrystalline platinum surface as well as the spatio-temporal concentration patterns associated with catalytic oxidation of carbon monoxide were imaged by means of photoemission electron microscopy (PEEM). For CO and O2 partial pressures in the 10(-4) mbar range and at temperatures between 420 and 560 K different categories of pattern formation are observed which may be correlated with similar features observed previously with low-index single crystal planes, namely bistable behavior, propagating reaction fronts as well as spirals and target patterns. A novel effect concerns the appearance of regions with work functions considerably below those of the respective clean surfaces which are presumably due to the formation of subsurface oxygen species.