INTRINSICALLY UNSTABLE BEHAVIOR DURING THE OXIDATION OF CARBON MONOXIDE ON PLATINUM (OSCILLATIONS, CHAOS, CATALYST)

Intrinsically unstable behavior--oscillations in particular--observed during the oxidation of carbon monoxide on platinum was investigated. This included a literature review which revealed several facts: (a) the reproducibility of data is poor, even under carefully controlled conditions (b) the state of the catalyst surface is critical (c) observed phenomena are often very complex and difficult to characterize (d) a large number of models have been proposed for the reaction behavior but the link between theory and experiments is still poor and (e) models involving the non-uniform surface states are being developed and show good promise.Experiments were conducted on the reaction on a platinum ribbon with a CSTR designed to approach isothermality on the catalyst surface and to provide as clean an environment as possible. Oscillations, reproducible in a qualitative sense, were observed at a number of states. When the reaction was allowed to proceed indefinitely, a slow continuous deactivation characterized by a decrease in a time-average conversion was observed. The observed behavior was aperiodic and strongly suggested "chaotic" behavior.Two numerical data analysis techniques, based on the concept that chaotic behavior is represented by a "strange" attractor and that the dimension of the attractor should be non-integer, were used to analyze the data. The results strongly indicate that the behavior is truly "chaotic" and mathematical models should incorporate at least four independent state variables.The character of the surface of a platinum ribbon was investigated with use of Auger electron spectroscopy. The effect of heating the ribbon in an oxygen atmosphere and then in a CO/air mixture on the chemical composition of the surface was quantified. Silicon was shown to segregate to the platinum surface after extended exposure to the CO/air mixture.