Effect of Severe Thermal Aging on Noble Metal Catalysts

Abstract Both sintering and activity behaviours over noble metal catalysts aged in oxidative atmospheres with various O 2 contents at 1100°C (or 1000° C) for 5 h were systematically characterized. With increasing O 2 contents, catalytic activities over aged Pt, Rh, and Pt/Rh catalysts decreased, and, in contrast, those over aged Pd and Pd/Rh catalysts increased. While, an order of sintering for the noble metal particles on aged catalysts agreed closely to that of the each percentage conversions as well as to that of vapour pressures of respective catalyst species, such as noble metals or their oxides. Selectivity profiles of the aged catalysts for converting NO and O 2 in a simulated exhaust gas were characteristic ones. It is confirmed through the above results that the performance of aged catalysts are tightly governed by the properties of noble metals and the selectivity data are also important for exploring the catalytic activities, in particular, over multi-functional catalysts such as automotive exhaust ones.