Thermal stabilisation effects of Zr buffer layer on nanometric Rh overlayer catalyst formed on metal foil substrate

Abstract

A nanometric Rh overlayer formed on a metal foil substrate enables much higher turnover frequencies in NO reduction than the Rh nanoparticles used in conventional three-way catalysis. However, the thermal stability of the Rh overlayer structure needs to be improved for practical applications. In the present study, a Zr buffer layer inserted between the Rh overlayer and the foil substrate efficiently overcame the thermal deterioration at 900 °C for 25 h. A honeycomb catalyst consisting of a 7 nm-thick Rh overlayer, a 500 nm-thick Zr buffer layer and a 30 μm-thick Fe–Cr–Al metal (SUS) foil was prepared by pulsed arc-plasma deposition. After thermal ageing, the Rh/Zr/SUS demonstrated steep light-off characteristics in simulated NO–CO–C₃H₆–O₂ reactions. In contrast, the neat catalyst without the buffer layer (Rh/SUS) was totally deactivated by the Al₂O₃ passivation layer that formed over the active Rh overlayer. The Zr buffer layer preserves the outermost surface of the Rh overlayer by blocking the interaction between the Rh and Al₂O₃ layers. Consequently, the Rh surface coverage of Rh/Zr/SUS exceeded 80% after thermal ageing at 900 °C, versus almost 0% for Rh/SUS.