Acoustic excitation influence on the oscillatory CO oxidation reaction over a Pt{110} crystal

Kinetic oscillations in the CO oxidation reaction rate have been initiated when a thin Pt{110} crystal, bonded onto the surface of an interdigital transducer device, was excited with surface acoustic waves (SAWs – Rayleigh waves). The oscillations were square waves with periods between 500 and 1000 s and became regular after an induction period of the order of 40 min following the acoustic excitation of the catalyst. A very small influence of further acoustic excitation has been observed when it occurs at the maximum of the reactivity, conversely, a four-fold increase in the reaction rate was recorded if the SAW excitation was applied when the system exhibited minimum reactivity. It is therefore concluded that acoustic excitation is effective only when the reaction rate is limited by the rate of oxygen adsorption. Hence, the effect of SAW is to increase the sticking probability of oxygen. The SAW chemical effect is not associated with a purely thermal effect, since the catalyst temperature was accurately stabilised during the course of the experiments by means of a feedback controlled temperature regulator.