SPATIOTEMPORAL PATTERN-FORMATION IN CATALYTIC REACTIONS ON SINGLE-CRYSTAL SURFACES

Two oscillatory surface reactions, namely catalytic CO oxidation and the catalytic reduction of NO with various agents (CO, H-2, NH3), have been studied on Pt single crystal surfaces at low pressure (p < 10(-3) Torr) using spatially resolved techniques. Both Turing structures as well as chemical wave patterns with varying degrees of complexity were observed. The facetting of Pt(110) in catalytic CO oxidation is discussed as an example for the experimental realization of a Turing structure. A detailed microscopic picture is available for the formation of the facet pattern as demonstrated by a Monte Carlo simulation. The catalytic reduction of NO with CO and NH3 on Pt(100) serves as an example for the transition from ordered to turbulent spatiotemporal patterns. The spatial coherence in these patterns is determined by the competition between long-range synchronization via gas-phase coupling and short-range coupling via the surface diffusion of a mobile adsorbate.