• Citer

Real time nanoscale imaging of a catalytic reaction: the case of NO2 + H2 on platinum

par Barroo, Cédric ;De Decker, Yannick ;Devred, François ;Visart de Bocarmé, Thierry ;Kruse, Norbert
Référence Interdisciplinary Surface Science Conference – ISSC (19: 2013-03-25->28: Nottingham, Royaume-Uni)
Publication Non publié, 2013-03-25

Communication à un colloque

• Détails
• Contenu

Résumé :

As NOx emissions from vehicles may cause severe health damages, their abatement remain a major challenge for catalyst makers. There is a lack of basic knowledge about the elementary processes involved during deNOx reaction at the surface of the catalyst. In particular, the structural influence on the strongly non-linear reaction kinetics remains an issue of fundamental catalysis studies. With this background, the catalytic reduction of NO2 has been investigated on the extremity of platinum tips samples by means of Field Emission Microscopy (FEM). By its size (~40nm diameter) and morphology (hemispherical), the apex of the tip is a good model of a single catalytic nanoparticle, exhibiting simultaneously a number of different crystallographic facets acting in a synergistic way. The presence of adsorbates induces changes in the work function, and the qualitative surface composition can be investigated by monitoring local variations of the current density, which translates into brightness patterns that can be monitored and analysed by video techniques. Self-sustained periodic oscillations were observed, and within the time resolution of the acquisition system (20 ms), all active facets reacted simultaneously.Field Ion Microscopy (FIM) provides a direct image of the tip samples with atomic resolution. Experiments by FIM have shown that surface reconstruction occurs during the reaction at 390 K: the morphology changes from hemispherical towards nearly pyramidal so as to produce patterns indicating the extension of {113} facets to the detriment of vicinal orientations. This reconstruction influences the catalytic activity.The combination of both FIM/FEM made possible to to image with nanoscale resolution a catalytic reaction in real time at the catalyst surface. A reaction mechanism for the observed kinetic oscillations is finally proposed.