A realistic kinetic Monte Carlo simulation of the faceting of a Pt(110) surface under reaction conditions

The faceting process on Pt(110) is studied with the help of a kinetic Monte Carlo model taking into account realistic Pt-Pt, Pt-CO, and Pt-O interactions. The activation energies of the allowed atomic steps are estimated using available computational and experimental data. The model well reproduces the region in the parameter space where faceting occurs. Under kinetic instability conditions, the simulated faceted pattern forms a periodic hill and valley structure with a lateral periodicity of approximately 140-170 A, which is comparable with experimental data. The simulations reproduce the development of faceting on a realistic time scale.

Critical behavior in an atomistic model for a bistable surface reaction: CO oxidation with rapid CO diffusion

We analyze critical behavior associated with the loss of bistability for an atomistic model for CO oxidation on surfaces in the limit of infinite diffusion of CO. The model includes infinite nearest-neighbor repulsions between adsorbed immobile O. We use a "hybrid" treatment incorporating a lattice-gas description of the O adlayer, but tracking just the number of adsorbed CO (which are randomly distributed on non-O sites). The critical exponents obtained from a finite-size-scaling analysis on LxL site surfaces with periodic boundary conditions show that the "hybrid" reaction model belongs to the mean-field universality class, despite strong spatial correlations in the O adlayer. We also quantify finite-size effects in the global bifurcation diagram, revealing a significant shift of the bistable region with decreasing system size. Our study elucidates fluctuation effects observed in experiments of CO oxidation on the nanoscale facets of metal-field emitter tips.

Catalysis on microstructured bimetallic surfaces

Microstructured bimetallic Pt/Rh and Pt/Ti surfaces have been employed to study the dynamics of catalytic NO reduction and the O(2)+H(2) reaction at low pressure (p<10(-3) mbar). Photoelectron emission microscopy and scanning photoelectron microscopy were used as spatially resolved in situ methods to image the local work function changes and to identify chemical changes in the substrate and in the adsorbate layer. It is shown that diffusional coupling leads to dynamic effects which are dependent on the macroscopic size (&mgr;m range). With alkali metals on the surface, stationary patterns form whose mechanism of formation has been studied in detail. (c) 2002 American Institute of Physics.

Catalytic CO oxidation on nanoscale Pt facets: effect of interfacet CO diffusion on bifurcation and fluctuation behavior

We present lattice-gas modeling of the steady-state behavior in CO oxidation on the facets of nanoscale metal clusters, with coupling via interfacet CO diffusion. The model incorporates the key aspects of the reaction process, such as rapid CO mobility within each facet and strong nearest-neighbor repulsion between adsorbed O. The former justifies our use of a "hybrid" simulation approach treating the CO coverage as a mean-field parameter. For an isolated facet, there is one bistable region where the system can exist in either a reactive state (with high oxygen coverage) or a (nearly CO-poisoned) inactive state. Diffusion between two facets is shown to induce complex multistability in the steady states of the system. The bifurcation diagram exhibits two regions with bistabilities due to the difference between adsorption properties of the facets. We explore the role of enhanced fluctuations in the proximity of a cusp bifurcation point associated with one facet in producing transitions between stable states on that facet, as well as their influence on fluctuations on the other facet. The results are expected to shed more light on the reaction kinetics for supported catalysts.