Design of advanced automotive exhaust catalysts

Rhodium (Rh) is a critical component of current automotive three-way catalysts (TWCs), particularly with regard to NOx and CO conversion at rich and stoichiometric air-fuel ratios (A/F). Rh supported on CeO2 was active for NOx and CO conversions but could be deactivated easily by high temperature aging. The cause of the deactivation is ascribed to the sintering of CeO2. ZrO2 incorporation into CeO2 is reported to have high thermal durability in terms of oxygen storage capacity (OSC), There has been no report showing direct experimental evidence that Rh-loaded on CeO2-ZrO2 mixed oxides induced effects on TWC performance improvement in the actual automotive exhaust. In the present paper, the Rh-CeO2 interaction contributing to NOx reduction and the catalytic behavior of Rh-loaded CeO2-ZrO2 mixed oxide is addressed. Incorporating CeO2-ZrO2 into a catalyst offered significant improvement in light-off and warmed-up performances in model gas test. Newly designed TWC including the Rh/CeO2-ZrO2 component were aged and evaluated on an engine dynamometer. Result of engine dynamometer evaluation also revealed that significant improvement in the thermal durability can be achieved by the utilization of the optimized Rh-loaded CeO2-ZrO2 mixed oxide. (C) 2000 Elsevier Science B.V. All rights reserved.