Thermal Ageing Effects in a Commercial Three-Way Catalyst: Physical Characterization of Washcoat and Active Metal Evolution

Abstract

The main system to reduce engine emissions of gasoline-fueled vehicles is represented by the three-way catalyst (TWC). The main catalyst of this system usually works in extreme conditions which induce a phenomenon called thermal ageing, the major way of catalyst deactivation. Increasingly stringent emissions standards require not only high efficiency in emissions abatement, but also maintaining the performances at high vehicle mileage. Automotive manufacturers need to accelerate testing methods and that should be representative of the ageing on vehicle, at the minimum expense in terms or time and cost. In order to develop and validate such methods, a deep understanding of all the microscopic processes associated with ageing is necessary. In this work we discuss a methodology for the study of the static thermal ageing of a commercial TWC. A specific washcoat extraction method was developed, and the separated washcoat was analyzed using XRD, TEM microscopy, Raman Spectroscopy and BET. These techniques allow to follow the main morphological and chemical changes in the sample: the loss of porosity, the evolution of crystalline phases and metal particles sintering and oxidation. The potential of Raman spectroscopy for the spatially resolved analysis of ageing is also highlighted. The results allowed to understand the process that involve the washcoat at high temperature.