Thermal Evolution of the Structure and Activity of Rh Overlayer Catalysts Prepared by Pulsed Arc-Plasma Deposition

Nanometric Rh overlayers were formed on Fe-Cr-Al stainless steel (SUS) foils by pulsed cathodic arc-plasma (AP) technique to investigate the thermal evolution of the structure and catalytic activity for stoichiometric NO-CO-C3H6-O-2 reaction. As-prepared Rh overlayer catalysts (Rh/SUS) with 2000-8000 AP pulsing showed steep light-off of NO, CO and C3H6 at around 250 degrees C and their conversions soon reached to almost 100%. After thermal aging at 900 degrees C in H2O/air, however, the catalytic activity was decreased to the different extent depending on the number of AP pulsing. The most significant deactivation was observed for the smallest numbers of AP pulsing (2000), because Al in the foil was oxidized during the aging to form a passivation layer of alpha-Al2O3, which covered the surface of the foil and decreased the surface concentration of Rh. To overcome this deactivation, the Rh overlayer was formed by AP after preheating the foil at 1000 degrees C in air. This modified preparation process enables the deposition of Rh overlayer on the highly crystalline alpha-Al2O3 layer at the surface of the foil, which is found to be much more stable against thermal deactivation.