SPATIOTEMPORAL CONCENTRATION PATTERNS ASSOCIATED WITH THE CATALYTIC-OXIDATION OF CO AND AU COVERED PT(110) SURFACES

Submonolayers of gold were evaporated onto a Pt(110) surface in order to study the influence of surface modification on the formation of spatiotemporal concentration patterns during catalytic oxidation of carbon monoxide as imaged by means of photoemission electron microscopy (PEEM). Already the presence of 0.05 monolayers of uniformly distributed Au atoms affects markedly the kinetic parameters and thereby the properties of spatiotemporal patterns. The excitable regime is reached at lower CO pressures than with bare Pt(110), the width of the oxygen waves and the wavelength of spiral patterns decrease, the velocity of front propagation is reduced, and the density of nucleation centers for waves increases. The observed effects can be rationalized on the basis of the well-established underlying mechanism in terms of modification of the sticking coefficients for oxygen and carbon monoxide and of the diffusion coefficient for adsorbed CO. Additional effects such as penetration of waves into a monostable region, refraction, etc., come into play if waves pass the border between surface areas with differing chemical properties. © 1995 American Institute of Physics.