Influence of the nature of the noble metal (Rh,Pt) on the low-temperature reducibility of a Ce/Tb mixed oxide with application as TWC component

Ceria-based mixed oxides have proved to be good alternatives to pure ceria as redox materials for advanced three-way catalysts. In this work, the behaviour of a Ce0.8Tb0.2O2-x, mixed-oxide sample and the corresponding oxide-supported Rh and Pt samples has been investigated. Special attention has been paid to the low-temperature redox response. Temperature-programmed desorption (TPD), temperature-programmed reduction and oxygen buffering capacity were used as experimental techniques. The evolution of reducibility was also followed by tunable high-energy x-ray photoemission spectroscopy, focussing on the surface information provided by Th 3d and Ce 3d core levels. The oxidation state of both Ce and Tb was followed during ultrahigh vacuum annealing of the three samples up to 750 K. Comparison of the XPS spectra for the different samples before and after annealing showed that the Ce4+ reduction was negligible but Tb4+ was gradually reduced to Tb3+. Furthermore, the TPD and XPS experiments are in good agreement, with the highest reduction rate corresponding to the Rh/CeTbOx sample. Copyright (C) 2002 John Wiley Sons, Ltd.