Structural evolution of Pt/ceria-zirconia TWC catalysts during the oxidation of carbon monoxide

The structural evolution of two Pt/ceria–zirconia catalysts, characterized by different amounts of supported Pt, was monitored by in situ X-ray diffraction during the anaerobic oxidation of CO at different temperatures. In a first phase, oxygen coming from the surface layers of the ceria–zirconia mixed oxide is consumed and no structural variation of the support is observed. After this induction time, bulk reduction of Pt/ceria–zirconia takes place as a step-like process, while the CO2 production continues at a nearly constant rate. This behavior is totally different from that of the metal-free support in similar reaction conditions, that show a gradual bulk reduction. In repeated oxidation–reduction cycles, it was observed that the induction time in Pt/ceria–zirconia is a function of the thermal history, of the amount of supported Pt and of the structural evolution of the samples. r 2003 Elsevier Inc. All rights reserved.