Platinum Loss from Alloy Catalyst Gauzes in Nitric Acid Plants

The loss of platinum from the catalyst gauzes used for the oxidation of ammonia in the manufacture of nitric acid has been studied for many years by catalyst producers and by users. In this paper, platinum losses from binary platinum-rhodium and ternary platinum-palladium-rhodium alloys, as well as from catalyst gauzes made of these materials, have been studied under laboratory and industrial conditions in atmospheric and medium pressure units, which are commonly found in P. R. China, and the rates of platinum loss and weight losses have been established. Adding a palladium component to the platinum-rhodium alloys or increasing the palladium content in platinum-palladium-rhodium alloys is clearly shown to decrease the rate of weight loss and the amount of platinum lost. This is attributed to the passive action of the palladium which accumulates on the surface and enriches the surface layer of the alloys, affecting both the platinum oxidation and platinum oxide reduction.