par Jacobs, Luc 
;Barroo, Cédric ;Visart de Bocarmé, Thierry
Référence Topics in catalysis
Publication Publié, 2020-11-01
;Barroo, Cédric ;Visart de Bocarmé, Thierry Référence Topics in catalysis
Publication Publié, 2020-11-01
Article révisé par les pairs
| Résumé : | At the industrial level, Ag catalysts in the form of silver crystals held by a silver gauze are largely used for formaldehyde production and ethylene epoxidation. These self-supported structures undergo surface reconstructions and morphological changes upon exposure to moderately high temperatures (473–900 K) and oxidising atmospheres. These phenomena have been studied and well understood on single crystal surfaces and polycrystalline foils: different oxygen surface and sub-surface species have been identified and reconstruction processes explained. To verify the scalability of the surface science results and ultimately understand these phenomena on catalysts at the industrial scale, further studies on more complex samples are needed. Attempts to close this “materials gap” have been carried out in this present study where experiments have been performed on model single catalytic nanoparticles, i.e. the apexes of field emitter tips, using both field emission (FE) and field ion (FI) microscopies. Pure Ag samples are exposed to a pressure of 3 × 10–5 mbar of O2 at temperatures up to 700 K. These conditions reflect those used on the industrial scale. Important surface/morphological reconstructions are observed both in FE and FI modes. For comparison, experiments have been repeated on Au-8.8%at. Ag field emitter tips, representative samples for Au–Ag catalytic nanofoams, using to 3 × 10–5 mbar of NO2 at temperatures up to 450 K. Similar behaviour are observed and the influence of the oxidising gas is discussed. |
