Effect of chromium migration from metallic supports on the activity of diesel exhaust catalysts

Fe–Cr–Ni and Fe–Cr–Al sintered spheres are explored as alternative support structures for automotive exhaust catalysts. Initially the activity of Pt supported on the metal support and on ceramic monoliths (cordierite) for the oxidation of CO and NO is comparable. However, after thermal aging at elevated temperatures (800 °C) and extended reaction times (24 h) the activity for the oxidation of NO of the catalysts supported on the Fe–Cr–Ni spheres decreases significantly, which is attributed to the migration of chromium from the metal bulk phase into washcoat. In the contrary, the aluminium present in the Fe–Cr–Al steel alloy formed a protective alumina barrier inhibiting the degradation of the catalyst after aging by blocking the migration of chromium to the surface.