Applied Catalysis B: Environmental 22 (1999) 167–178 Contribution of cerium/zirconium mixed oxides to the activity of a new generation of TWC Juan R. González-Velasco a,* , Miguel A. Gutiérrez-Ortiz a , Jean-Louis Marc a , Juan A. Botas a , M. Pilar González-Marcos a , Gilbert Blanchard b a Dpto. Ingenier´ ıa Qu´ ımica, Facultad de Ciencias, Universidad del Pa´ ıs Vasco/E.H.U., P.O. Box 644, E-48080 Bilbao, Spain b Rhodia Recherches, 52 rue de la Haie Coq, F-93308 Aubervilliers, Cedex, France Received 24 December 1998; received in revised form 5 March 1999; accepted 3 April 1999 Abstract The catalytic activity of several cerium/zirconium mixed oxides for TWC applications has been investigated with the aim of optimising the Ce/Zr composition. Their catalytic activity was surprisingly high, considering that no noble metal was present in the composition, particularly for oxidation reactions (CO and C 3 H 6 ), while their reduction activity was very small (NO). The specific activity of the mixed oxides for CO and C 3 H 6 was found to be the contribution of the individual specific activity of the single oxides. The best activity in practice (lowest T 0 and T 50 and highest X 773 ) was found for the mixed oxide with a Ce/Zr ratio of 80/20, as a combination of its high specific activity and the highest specific surface area. ©1999 Elsevier Science B.V. All rights reserved. Keywords: Ceria; Zirconia; Mixed oxides; Three way catalysts (TWC) 1. Introduction A large amount of investigation has been carried out on three way catalysts (TWC) technology in recent years. Although a lot of work has been directed to the study of the active phases, many researchers have focused their attention on the catalytic supports. Most of the supports for TWC applications contain a certain amount of ceria deposited on their surface. The reasons for this presence are multiple. Firstly, ceria is known to stabilise, on its surface, well-dispersed noble metals [1,2] thus favouring the amount of active * Corresponding author. Tel.: +34-94-6012681; fax: +34-94-4648500 E-mail address: iqpgovej@lg.ehu.es (J.R. Gonz´ alez-Velasco) surface per weight of the catalyst. Secondly, ceria is supposed to promote water-gas shift and hydrocarbon reforming reactions [2–7] that play a fundamental role in the elimination of CO and hydrocarbons in reduc- ing conditions, as well as CO oxidation in oxidising conditions [8]. And last but not least, ceria presents an interesting ability to act as a store of oxygen due to its low reduction potential [6,9], thus increasing the conversion of CO and hydrocarbons in reducing conditions and, particularly, the conversion of NO in oxidising conditions. At the same time, ceria presents an important prob- lem that prevents its use directly as a catalytic support in TWC: when exposed to temperatures about 1173 K or above — that can be reached easily by the cata- lyst in normal operation — it has a tendency to sinter 0926-3373/99/$ – see front matter ©1999 Elsevier Science B.V. All rights reserved. PII:S0926-3373(99)00054-5