Oscillatory behavior in the catalytic reduction of NO and NO2 with hydrogen on Pt field emitter tips

We studied the catalytic reduction of NO and NO2 with hydrogen on Pt using both Field Ion Microscopy (FIM) and Field Electron Microscopy (FEM) under various temperatures (395–530 K) and total pressures (10−4–10−2 Pa). Kinetic instabilities, including surface explosions and self-sustained oscillations of the catalytic production rate, were found for properly chosen external parameters and well developed tip morphologies. Oscillatory behavior was only found for pyramidally shaped tips. The {210} planes, most probably reconstructed under reaction conditions, acted as pacemakers. Reaction-diffusion fronts were found to propagate along the 〈100〉 zone lines. Very regular oscillations were registered for NO2 reduction in FEM studies. The oscillation periods increased with increasing NO2H2 ratios without significant changes in the pattern formation. The mechanism of the rate oscillations is driven by the autocatalytic decomposition and reaction of adsorbed NO.