The Chemical Characterisation of Rhodium-Platinum Surfaces

During the manufacture of nitric acid, rhodium-platinum gauzes are used to catalyse the oxidation of ammonia, an operation that results in a major reconstruction of the alloy surface. In this study, the effect of pretreatments, similar to those employed to prepare the catalysts for commercial use, have been examined to determine both the chemical and the physical effects on the surface. A successful pretreatment is shown to produce a generally clean, chemically receptive surface containing reactive crystal orientation sites. Additionally, the nature of the surface during catalyst operation has been investigated using a rapid quench facility in a miniature reactor. It has been established that, during catalyst operation, the surface of the catalyst is metallic, and not covered by an oxide layer as previously thought.