KINETIC OSCILLATIONS IN THE PT(100)/NO+CO SYSTEM - BIFURCATION-ANALYSIS

Under isothermal conditions at low pressure (10(-6) mbar), the NO + CO reaction on Pt (100) exhibits oscillatory changes in the N2 and CO2 Product partial pressures. A three-variable model based on the vacant-site requirement for NO dissociation has been formulated and analyzed by means of bifurcation theory. The constants used in the differential equations were all taken from experiment. The stability of the steady state and periodic solutions has been mapped out in one and two parameters. Kinetic oscillations were found to occur in two separate existence ranges: a large one above the stoichiometric ratio p(NO):p(CO) = 1:1 and a very small one below the stoichiometric point. The results demonstrate that the gross features of the experimentally observed oscillations are well reproduced by the model. The role of the internal parameters of the model was also analyzed with bifurcation theory. It was found that the model reacts most sensitively to those parameters which control the dissociation of NO. The fact that oscillations were only found on Pt (100) but not on Pt (111) and Pt (110) can be attributed to the lower dissociation efficiency of NO on the latter two orientations.