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Abstract:
Rate measurements of the reaction CO+O→CO2CO+O→CO2 on palladium(111) single crystal surfaces have been performed by means of mass spectroscopy under ultrahigh vacuum conditions. The total flux ΦΦ of the impinging reactants CO and O2O2 was held constant at 1MLs−11MLs−1, whereas its CO fraction YY was varied between 0 (pure O2O2) and 1 (pure CO). The measurements have been performed for surface temperatures between 370 and 510K510K and with a wide range of sampling times, evaluating the system parameter range for bistable behavior. Long-time measurements lasting several days proved the bistable behavior to result from two stable states rather than from slow processes not visible on usual experimental time scales. Pulselike modulations of the feed gas composition revealed the mechanisms confining the experimentally observed bistable range: the high CO fraction border of the bistability is given by the equistability condition of both states, whereas the other border is found to be associated with a saddle-node bifurcation in the corresponding system of reaction diffusion equations.
