An analytical SEM and XPS study of platinum–rhodium gauzes used in high pressure ammonia burners

Abstract

Abstract Scanning electron microscopy (SEM), combined with energy dispersive x‐ray analysis (EDS) and x‐ray photoelectron spectroscopy (XPS), has been used to study platinum–rhodium gauzes exposed to the conditions encountered during the oxidation of ammonia in high pressure converters. The intiial activation of gauzes in a hydrogen flame causes surface rearrangement and results in a slight Pt enrichment at the surface, while this trend is reversed in the further stages of ammonia oxidation in the reactor. Chemical analysis by both EDS and XPS techniques revealed that catalyst deactivation is caused by platinum (IV) oxide (PtO 2 ) evaporation from the gauzes. The remainder, rhodium, is entirely oxidized to non volatile Rh 2 O 3 . The results indicate that the formation of this compound continuously stimulates platinum diffusion toward the surface.