Automobile exhaust catalysis at the atomic scale: atom‐probe investigations on platinum alloys

A dedicated three‐dimensional atom‐probe has been fitted with an in situ high pressure/temperature reaction cell. This was used for studying the interaction of gases with Pt‐alloy surfaces typical of those employed in automotive exhaust catalysis. The reactions of nitric oxide (NO) and oxygen (O 2 ) on Pt and Pt–17.4 at.% Rh FIM specimens were explored, revealing a range of surface restructuring and segregation effects, which depend sensitively on catalyst composition, orientation, temperature and gas chemistry. Specifically, we observed that exposure of Pt–Rh to either NO or O 2 at 422–473 K and 10 mbar induced Rh surface segregation uniformly over the surface. However, on raising the temperature to 573 K or higher, the Pt–Rh{111} surface remained Rh‐enriched but the Pt–Rh{001} surface became severely Rh‐depleted. We attribute this observation to the possible diffusion of Rh species across the specimen apex, indicating that segregation occurs in directions both normal and parallel to the surface in Pt–Rh catalysts.