par Visart de Bocarmé, Thierry 
;Kruse, Norbert
Référence Topics in catalysis, 14, page (35-42)
Publication Publié, 2000-12-01
;Kruse, Norbert Référence Topics in catalysis, 14, page (35-42)
Publication Publié, 2000-12-01
Article révisé par les pairs
| Résumé : | This paper presents two case studies of adsorbate-induced surface reconstruction, on the one hand, and dynamical reaction imaging along with local chemical probing, on the other hand. The first one deals with the oxygen-induced reshaping of 3D Rh crystals. Field ion microscopy (FIM) was applied to image in real-space the change from a nearly hemispherical shape in the absence of oxygen toward a polyhedral one in the presence of oxygen. Shape transformation occurs at temperatures of 380–550 K and is associated with the appearance of facets with {111} and {001} orientation. The only high-index planes present in the polyhedral form are of {137} symmetry. (1×2) and (1×3) missing-row reconstructions appear in the {113} and {011} planes. The polyhedral form has also been imaged under in situ conditions of the oxygen–hydrogen reaction on Rh at 505 K. The second case study deals with kinetic non-linearities occurring in the NO2 reaction with hydrogen on the surface of a 3D Pt crystal reconstructed to a top- and edge-truncated pyramid. The reaction was found to ignite in the {012} corner planes of the crystal. One-dimensional wavefronts were subsequently observed to move along the <211> zone lines. These studies were performed by video-FIM and could be correlated with a local chemical analysis by time-of-flight mass spectrometry of ionised species. The mass spectrum provided information on water product (H2O+ and H3O+) and NO intermediate formation. Strong fluctuations in the (NO2)+ current indicated the occurrence of NO2 surface diffusion. These species are most likely responsible for the field ion image formation. |
