Mono- and multi-metallic (bi- and tri-) Pt, Pd and Rh supported on cerium-promoted alumina (La Roche, SAS-1/16) catalysts were tested for activity as TWC, both fresh [G.C. Koltsakis, and A.M. Stamatelos, Progr. Energy Combust. Sci. 23 (1997) 1] and after accelerated aging. Aging consisted of a treatment at 900 degrees C for 5h during which an oxidizing (2.5% O-2, 10%, H2O, in N-2) and a reducing (5.0% CO, 10% H2O, in N-2) feedstream were cycled at 0.017 Hz through the catalyst. Activity tests were carried out by increasing temperature from 100 to 600 degrees C at 3 degrees C min(-1), while two oxidizing and reducing (+/-0.5 A/F) feedstreams were alternately (1 Hz) fed through the reactor at 125 000 h(-1) (STP). Conversion was continuously analyzed. Light-off temperature, T-50, conversion at 500 degrees C (normal running temperature), X-500, and the stoichiometric window (A/F from 14.13 to 15.13) for stationary feedstreams, were determined. (C) 2000 Elsevier Science B.V. All rights reserved.