Energy-Resolved Field Ion Spectroscopy of Surface Reactions: H₂/O₂ and H₂/H₂O on Platinum

Abstract
Applications of field ion mass and appearance energy spectroscopy on catalytic surface reactions are reviewed. The investigations have been stimulated by in-situ FIM observations in the group of the late J.H. Block suggesting that single, active sites can be visualized. We have especially examined the energetics and kinetics of H₂- O₂ and H₂-H₂O reactions on [001] oriented Pt-tips. For single surface sites field ion yields have been measured as a function of Hz partial pressure showing (different) hysteresis behavior for both reaction systems. For H₂/O₂/Pt the results agree qualitatively with features earlier observed at field-free conditions. This finding and the different kinetics of the two reaction systems suggest a less pronounced influence of the applied electric field on the surface catalyzed H20 formation for H₂/O₂/Pt. At distinct control parameter (pressures, temperature) dynamic phenomena, such as kinetic instabilities and oscillating reaction diffusion fronts, were characterized by probe hole FIM combined with FIMS and FIAPS. For H₂/O₂/Pt comparative measurements have recently revealed a different behavior in FIM and FEM modes possibly caused by the different facets contributing to FI and FE emission currents.