Morphology changes of Pt-foil catalyst induced by temperature-controlled ammonia oxidation near atmospheric pressure

Abstract

Reaction-induced changes of the morphology of a Pt foil catalyst during ammonia oxidation were investigated in a temperature-controlled way for partial pressures of oxygen and ammonia around 4.5 and 3 kPa, respectively, and at temperatures between 20 and 700 °C. The presence of the feed mixture (ammonia and oxygen) was required to induce surface roughening. Moreover, the reaction temperature controlled the type of restructuring of the Pt surface, that is, either into rows of parallel facets where facet size increased with temperature, or as bulky microcrystals protruding from the surface. Surprisingly, reaction-induced surface faceting was already observed at 286 °C. Between 286 and 374 °C adsorbate-enhanced surface diffusion of Pt is suggested to account for the surface restructuring well below temperatures reported for significant Pt transport through the gas phase via volatile PtOx.