Dynamics and pattern formation on microcomposite and addressable catalytic surfaces.

摘要

Catalytic reactions on single crystal surfaces under low pressures exhibit rich non-linear phenomena, such as steady state multiplicity and rate oscillations. In addition, as a result of surface diffusion, they spontaneously form spatial and spatiotemporal concentration structures ("patterns") on the surface. Both of these features can greatly affect the reactive activity. In this Thesis, we combine dynamical systems and bifurcation theory, with active collaboration with experimentalists, to investigate the spatiotemporal dynamics and pattern formation during CO oxidation on Pt(110). We focus on features which affect the dynamics. The underlying theme is how externally imposed perturbations like surface heterogeneity (such as that caused by using a composite, micropatterned catalyst) and temperature heterogeneity can profoundly influence catalytic activity and dynamics.; The first part of the thesis deals with the dynamics on microcomposite catalysts, which are single crystal catalytic surfaces decorated with controlled, micron-scale heterogeneity fields. The effect of active boundary and its geometry in two dimensions on the spatiotemporal patterns is our focus. Two case studies are presented. In the first case we show how the shape and speed of reactive waves during CO oxidation can be dramatically affected by the second component of the composite. Our second experimental/modeling example consists of manipulating the locations of transitions between different branches of kinetic hysteresis.; In the second part of the thesis, we use a moving focused laser beam to heat Pt(110) surface for the realization of "addressable" catalyst. This allows the modification of surface catalytic activity in both time and space. We study, both computationally and experimentally, the initiation of new pulses and fronts using the focused laser beam, the interaction between the laser spot and existing pulses, and finally the possibility of reaction rate enhancement through laser movement.