On the kinetics of oscillating reactions: [formula omitted] and [formula omitted] on platinum

Abstract

Field ion microscopic and spectroscopic analyses have been carried out for individual, catalytically active sites of a Pt tip exposed to a continuous flow of H 2O 2 and H 2H 2O gas mixtures. Product ion yields (H 2O +, H 3O +) are measur function of H 2 pressure showing hysteresis and bistability; transitions between different reactive phases at distinct critical H 2 pressures are observed. For H 2/O 2/Pt, results agree qualitatively with previous (field free) experimental data and recent theoretical predictions thus indicating a minor influence of the applied electric field. For the oscillating H 2 H 2 O rea system the kinetics differs markedly. Local fluctuations and oscillating reaction diffusion fronts are imaged by probe hole FIM and are analyzed simultaneously using field ion appearance energy spectroscopy. Different surface-reaction pathways are found in different kinetic phases.