Pt-Catchment Using Pd/Au Alloys: Effect of Enhanced Diffusion

We have studied a series of Pd/Au alloys as Pt-catchment materials, both in lab-scale experiments and in an industrial ammonia oxidation plant. Our focus has been on how bulk Pt diffusion affects grain reconstruction in Pd/Au alloys (91/9 and 50/50 at. %) during Pt-catchment, performed by studying both polycrystalline (as produced) and quasi-monocrystalline (preannealed in vacuum) wires. The grain reconstruction is reduced when alloying Pd with Au, and it is almost absent for Pd/Au (50/50 at. %). For all Pd-containing samples with a quasi-monocrystalline grain structure, the restructuring is limited in short (<20 days) laboratory experiments but present in the 5 month industrial experiment. Notably, the Pd/Au (50/50 at. %) alloy shows a low degree of restructuring in all experiments but a reduced Pt-catchment in the industrial experiment. The mechanism for grain reconstruction of Pd/Au alloys is discussed, along with the role of the Kirkendall effect and the internal porosity on wire restructuring.