| Complex behavior during heterogeneous catalytic reactions such as bistability, reaction rate oscillations, and spatiotemporal pattern formation has been known for several decades. On polished metal surfaces operated under high vacuum conditions (<10-3 Torr), reaction rate oscillations are purely due to highly nonlinear surface kinetics which give rise to spatiotemporal patterns when coupled with surface diffusion. Experimental observation and characterization along with detailed theoretical investigations of these patterns have revealed a great deal of information about the underlying kinetic processes of many catalytic systems. This thesis explores the nonlinear dynamics of CO oxidation and the reduction of NO by NH3 on platinum catalysts experimentally and through microkinetic modeling.; Beyond the characterization of spontaneous pattern formation, there has recently been increasing interest in local manipulation of pattern-forming systems as a potential means to control the reactivity and selectivity of the catalyst. By directly introducing reactants through a capillary tube near the catalyst surface, we are able to locally perturb the gas phase composition and, by extension, the local surface coverage and reaction rate. Dosing of hydrogen into the system during CO oxidation allows us to locally poison the catalyst surface and to create novel metastable CO islands. Hydrogen dosing was also used to induce oscillations in a system that is stable in the absence of dosing. |
