Effects of external global noise on the catalytic CO oxidation on Pt(110)

Oxidation reaction of CO on a single platinum crystal is a reaction-diffusion system that may exhibit bistable, excitable, and oscillatory behavior. We studied the effect of a stochastic signal artificially introduced into the system through the partial pressure of CO. First, the external signal is employed as a turbulence suppression tool, and second, it modifies the boundaries in the bistable transition between the CO and oxygen covered phases. Experiments using photoemission electron microscopy (PEEM) together with numerical simulations performed with the Krischer-Eiswirth-Ertl (KEE) model are presented.Comment: 15 pages, 7 figures, accepted in J. Chem. Phy

Simple reflection anisotropy microscopy set-up for CO oxidation studies

Reflection anisotropy microscopy (RAM) is a tool to monitor the optical anisotropy of surfaces with spatial resolution (Rotermund et al 1995 Science 270 608–10). It has been applied to pattern formation during CO oxidation on Pt(110), where it provides a high sensitivity for surface reconstruction and partially also for the coverage with reaction educts (Heumann 2000 Dissertation TU-Berlin). However, the spatial resolution of RAM and the alignment procedure of the optical components were not satisfactory. Here, we give a detailed description of a new set-up, which employs a simple polarizing beam splitter cube as an analyser instead of a Foster prism, offering a higher spatial resolution (<10 μm) and easier alignment of the optical components while retaining the high sensitivity for surface structure. Polarization contrast and spatial resolution of the new set-up are systematically measured, and applications to CO oxidation on uniform and microstructured Pt(110) single crystals are presented

Period doubling and spatiotemporal chaos in periodically forced CO oxidation on Pt(110)

Periodic forcing of chemical turbulence in the catalytic CO oxidation on Pt(110) can induce a period doubling cascade to chaos. Using a forcing frequency near the second harmonic of the system's natural frequency, and carefully increasing the forcing amplitude, the system successively exhibits spiral wave turbulence, resonant pattern formation, and chaotic oscillations. In the latter case, global coupling induces strong spatial correlation. Experimental results are presented as well as numerical simulations using a realistic model. Good agreement is found between experiment and theory. The results give further insight into the complex nature of reaction-diffusion systems and are of high importance regarding control strategies on such systems. The presented setup enhances the range of achievable dynamical states and allows for new experimental investigations on the dynamics of extended oscillatory systems

Enhancement of surface activity in CO oxidation on Pt(110) through spatiotemporal laser actuation

We explore the effect of spatiotemporally varying substrate temperature profiles on the dynamics and resulting reaction rate enhancement for the catalytic oxidation of CO on Pt(110). The catalytic surface is "addressed" by a focused laser beam whose motion is computer-controlled. The averaged reaction rate is observed to undergo a characteristic maximum as a function of the speed of this moving laser spot. Experiments as well as modelling are used to explore and rationalize the existence of such an optimal laser speed.Comment: 9 pages, 12 figures, submitted to Phys. Rev.

Geometry-induced pulse instability in microdesigned catalysts: the effect of boundary curvature

We explore the effect of boundary curvature on the instability of reactive pulses in the catalytic oxidation of CO on microdesigned Pt catalysts. Using ring-shaped domains of various radii, we find that the pulses disappear (decollate from the inert boundary) at a turning point bifurcation, and trace this boundary in both physical and geometrical parameter space. These computations corroborate experimental observations of pulse decollation.Comment: submitted to Phys. Rev.

Guiding chemical pulses through geometry: Y-junctions

We study computationally and experimentally the propagation of chemical pulses in complex geometries.The reaction of interest, CO oxidation, takes place on single crystal Pt(110) surfaces that are microlithographically patterned; they are also addressable through a focused laser beam, manipulated through galvanometer mirrors, capable of locally altering the crystal temperature and thus affecting pulse propagation. We focus on sudden changes in the domain shape (corners in a Y-junction geometry) that can affect the pulse dynamics; we also show how brief, localized temperature perturbations can be used to control reactive pulse propagation.The computational results are corroborated through experimental studies in which the pulses are visualized using Reflection Anisotropy Microscopy.Comment: submitted to Phys. Rev.

Control of spatiotemporal chaos in catalytic CO oxidation by laser-induced pacemakers

Control of spatiotemporal chaos is achieved in the catalytic oxidation of CO on Pt(110) by localized modification of the kinetic properties of the surface chemical reaction. In the experiment, a small temperature heterogeneity is created on the surface by a focused laser beam. This heterogeneity constitutes a pacemaker and starts to emit target waves. These waves slowly entrain the medium and suppress the spatiotemporal chaos that is present in the absence of control. We compare this experimental result with a numerical study of the Krischer–Eiswirth–Ertl model for CO oxidation on Pt(110). We confirm the experimental findings and identify regimes where complete and partial controls are possible

Spatiotemporal concentration patterns in a surface reaction: Propagating and standing waves, rotating spirals, and turbulence

Laterally varying surface concentrations associated with the oscillatory oxidation of carbon monoxide on a Pt(110) surface were imaged by photoemission electron microscopy. Depending on the applied conditions, a large variety of spatiotemporal patterns were observed that are characteristic for the nonlinear dynamics of reaction-diffusion systems